Emerging for non-invasive heparin delivery systems: recent advances, barriers, solutions, and applicability

Abstract

Nowadays, the use of unfractionated low molecular weight heparins through intravenous and subcutaneous routes has been limited by several delivery challenges. These include pharmacological activity fluctuations, bleeding issues, and numerous manufacturing restrictions. To address these issues, several efforts have been taken to find alternative routes for this medication. Unfortunately, the past and recent reviews were mainly explored the oral dosage forms of heparin and the other possible indications in practice. This review focuses on emerging efficient and non-invasive heparin options such as buccal, sublingual, oral, rectal and vaginal, transdermal, pulmonary and nasal. To do that, the past and recent studies were categorized into three main groups: (1) Conventional invasive heparin delivery methods; (2) Novel non-invasive heparin delivery systems; and (3) Heparin-based nanoparticles. The main challenges to use non-invasive heparin delivery systems were found to be negative charge and high molecular weight of heparin. Besides, the biological, biophysical, and pharmacological constraints could also limit the benefits of these alternatives. To overcome these issues, the following mechanisms have been used to enhance the delivery of heparin through several routes: (1) Improvement of cell-membrane penetration, (2) Changing of the tight-junctions, (3) Promoting the lipophilicity and (4) Preserving against acidic pH of the stomach. The applicability of alternative delivery options for heparin was mainly affected by overcoming the main penetration barriers. Nanoparticles were found to be effective in increasing the permeability, absorption, bioavailability and bioactivity of heparin.

Introduction

Heparin, a highly sulfated polyanionic glycosaminoglycan drug with molecular weight (MW) ranging from 3000 to 30000 Da, was discovered by McLean and William H. Howell since 1916 in Toronto, Canada (Jamshidovich 2024). It is widely used for more than 80 years as an anticoagulant, anti-inflammatory and antithrombotic for the prevention and treatment of thrombotic events. The other indications for heparin may also include treatment of thrombosis-related pulmonary diseases, inhibition of metastases, atherosclerosis and angiogenesis of cancer, nephro- and neuro-tissue protection, as well as acting as antimicrobial agents against viruses and protozoa (Hogwood et al. 2023). It exerts its primary anticoagulant effect by inactivation of thrombin and stimulation for factor Xa via an antithrombin (AT)-dependent mechanism (Fig. 1). Heparin interacts with AT via a high-affinity pentasaccharide found on approximately one-third of heparin molecules. Heparin should bind to both the coagulation enzyme and AT in order to block thrombin, whereas the inhibition of factor Xa was not required for enzyme binding. Heparin molecules did not have enough chain length for bridging the gap between thrombin and AT, and so it was not be able to inhibit thrombin. In contrast, relatively tiny heparin fragments with the pentasaccharide sequence can block factor Xa via AT pathway (Hogwood et al. 2023). Heparin not only blocks fibrin formation, but also it can prevent thrombin-induced activation of platelets as well as factors V and VIII. Heparin can be classified based on its molecular weight into two groups: (1) Unfractionated heparin (UFH, MW: 3000–30,000 Da), and (2) Fractionated low-molecular-weight heparins (LMWHs, MW: 2000–9000 Da). LMWHs have a lower frequency of toxicity, less protein binding, longer half-life periods, higher bioavailability, and greater anti-FXa activity than UFH (Arachchillage et al. 2024). This drug is usually administrated via parenteral routes since it has a high molecular weight and negative charge which display various limitations for effective pharmacotherapy of thrombosis. These include variation in pharmacokinetic and physiochemical properties, adverse events such as bleeding complications, and manufacturing restrictions (Shute 2023). For example, heparins have a strong affinity for plasma proteins which may lower their bioavailability and cause a variety of anticoagulant effects. These proteins are histidine-rich glycoprotein, platelet factor 4, vitronectin, and von Willebrand factor. Besides, heparin has complex pharmacokinetics; for instance the clearance for this drug can be occurred through several pathways (Hirsh et al. 2001). These include fast and saturable clearance of heparin by the endothelial cells and macrophages. In the other hand, heparins are also cleared from the plasma by a slower and non-saturable renal mechanism. Consequently, the anticoagulant effect of heparin is not linearly related to dose in the therapeutic range. The biologic half-life of heparins fluctuates between 30 min (after a 25 U/kg IV bolus dose) and 150 min for 400 U/kg bolus dose (Hirsh et al. 2001; Zhang et al. 2025). In terms of safety, patients may produce IgG antibodies in response to heparin administration that can lead to target the heparin–platelet factor 4 complex. These antibodies activate platelets and increase the risk of subsequent arterial and venous thrombosis (Zhang et al. 2025). In contrast, various non-invasive routes of heparin (oral agents, rectal and vaginal, transdermal, pulmonary and nasal) could be used as the feasible, safe, and effective alternative options of injectable heparin (Motlekar and Youan, 2006; Zhang et al. 2025). For example, oral options have several advantages such as ease of administration, fast cellular recovery, high vascularization, non-invasive, and bypassing of the gastrointestinal system and liver clearance. Additionally, the rectal and vaginal methods offer several benefits for local and systemic medication delivery such as increased the higher blood circulation and a large surface area for absorption. Transdermal drugs bypass first-pass metabolism and the gastrointestinal tract by delivering the drug through the skin. This approach effectively works for drugs that are strongly metabolised or poorly absorbed orally (Motlekar, and Youan, 2006; Zhai et al. 2021). Besides, the rapid clinical response, vast absorptive surface area, predictable absorption kinetics, and lower risk of systemic side effects make inhaled approaches such as nasal and pulmonary routes the beneficial alternative choices for delivering heparin (Zieliński et al. 2019). In accordance, nanovesicles have been shown to be beneficial in improving the permeability, absorption, bioavailability, and bioactivity of heparin (Pilipenko et al. 2019). As a result, this study aims to bridge the gaps in the existing research regarding the delivery barriers of injectable heparin, specifically the lack of non-invasive delivery methods. Therefore, this work may also open the discussion of future research requirements. To do that, this review divides the previous data that explored the heparin delivery systems into three categories: (1) Traditional parenteral and invasive methods for delivery of heparin; (2) The novel non-invasive heparin delivery systems; and (3) Heparin-based nanoparticles. The past and recent in vitro and in vivo studies as well as the clinical trials that were conducted for each delivery system were also organized and summarized in tables.

Fig. 1.

The mechanisms of thrombin formation and coagulation pathways (Zhang et al. 2025)

Results

Traditional parenteral and invasive methods for delivery of heparin

Administration routes and available options

The UFH and LMWHs are widely administered by intravenous or subcutaneous routes. Newer synthetic heparin derivatives such as fondaparinux (a penta-saccharide) and its analogue (idraparinux) are still given by subcutaneous injection. These synthesized compounds demonstrated better anticoagulant activity and predictable pharmacokinetic characteristics through inhibition of factor Xa (Bick et al. 2005; Li and Li 2025). Idraparinux interacts to AT more strongly than fondaparinux via an additional interaction with the extra sulphate group at C3 of the H glucose unit and hydrophobic interactions. Because of the enhanced sulfation, this drug has a 30-fold higher binding affinity to AT than fondaparinux and a stronger anti-factor Xa activity. Idraparinux has a substantially longer elimination half-life of around 120 h in clinical trials, allowing for once-weekly administration (Li and Li, 2025). Unfortunately, idraparinux did not receive FDA regulatory approval due to serious bleeding problems. Besides, fondaparinux is one of the most expensive available heparins. The entire synthesis of fondaparinux is particularly complicated because of the difficulty in regio- and stereo-selective glycosidic linkages among the glucosamine, glucuronic acid, and iduronic acid building blocks (Li and Li 2025).

Recent advances

Non-eluting and microsphere film stents have recently emerged as invasive methods of enhancing parenteral heparin administration. For example, heparin-loaded zein microsphere films were used to enhance the hemocompatibility of drug-eluting stents (Medina et al. 2004; Yu et al. 2025). Furthermore, the release rate of heparin from microsphere film after 12 h was increased to 33.5 ± 1.2%, followed by a"slow release"phase where approximately 55% of the heparin had released after 20 days. Non-eluting stents have also been used to minimize the problems of the thrombosis following implantation (Yu et al. 2025).

Challenges and clinical limitations

The parenteral and invasive heparin formulations including stents are not typically preferred by patients for several reasons. Furthermore, they have extensive manufacturing considerations such as isotonicity, sterility, stability, and requirement to be free from pyrogen and residuals. Besides, these routes have also several pharmacokinetic and pharmacodynamic barriers (Bouget et al. 2022). These challenges involve enzymatic degradation by heparinase in the liver and intestinal microflora, chemical instability at acidic pH, and limited absorption due to the presence of the epithelial and mucosal barriers. Furthermore, desulfation and glycoside residue metabolism might happen at the acidic pH of stomach, unless heparinase-derived heparin fragments are added (Yu et al. 2025). Additionally, hydrolysis can also result in chemical instability for heparin by cleaving glycosidic bonds, altering molecular integrity, and consequently deviating from its therapeutic specifications (Bouget et al. 2022).

The previous studies have shown that the heparin administered through a stent did not effectively prevent restenosis due to several reasons. Furthermore, the performance of these stents is highly affected by their designs and configuration. Additionally, the simple proximity of delivery devices including heparin stents to tissues could not guarantee the appropriate targeting. The main cause for that is the great difference between local concentrations and mean concentrations due to physiological transport forces (Bouget et al. 2022; Medina et al. 2004). Thus, the previous challenges such as safety, pharmacokinetic variability, and manufacturing constraints can be solved by developing effective non-invasive heparin delivery systems and loading this drug into nanovesicles.

The novel non-invasive heparin delivery systems

Buccal heparin delivery

The buccal cavity has recently received a lot of interest as a method of systemic administration for macromolecular drugs such as heparin. It has many benefits including ease of use, fast cellular recovery, high vascularization, non-invasive, and bypassing of the gastrointestinal system and liver clearance. However, there are certain restrictions on delivery of buccal drugs. These include the possibility of inadvertently ingesting the delivery device, salivary scavenging, and the barrier qualities of the buccal mucosa (Senel et al. 2001). Furthermore, the oral cavity poses significant biological obstacles for systemic administration of buccal drugs. For example, the drug must be released from the formulation, then move to the delivery site (e.g., buccal or sublingual area) and penetrate through the mucosal layers. The pH, fluid volume, pKa, logP, stability, enzyme activity, and oral mucosal permeability were also considered important factors in this process. Additionally, the other physiochemical issues include high molecular size, and poor lipophilicity that can also limit the penetration and absorption of heparin from the buccal mucosa (Mouftah et al. 2016; Senel et al. 2001). To overcome these issues, the optimal buccal drug delivery system should sustain an intense adhesion with the buccal mucosa for an extended period of time, improve penetration and offer stabilization or protection characteristics for the given macromolecule. Several approaches have been developed to enhance the buccal delivery of heparin. These methods could involve: (1) The development of mucoadhesive nanoparticulate carriers with longer residence durations and possibly higher bioavailability; and (2) The use of chemical permeation enhancers, enzyme inhibitors, and mucoadhesive materials as adjuvants (Engelberg 1959). Enzyme inhibitors can suppress the degradation of heparin by catalytic enzymes in oral cavity, thus they increase the amount of heparin available for absorption. Mucoadhesive nanoparticulate carriers can be defined as nano-biological materials used to increase the attractive forces between a drug loaded in these nanovesicles and mucous membrane of buccal area. Moreover, cationic polymethacrylate (inert materials, harmless and less absorbed in gastrointestinal tract) nanoparticles were used to entrap LMWHs for buccal macromolecular drug delivery (Mouftah et al. 2016; Ortiz and Morales 2020). Polymethacrylate nanoparticles can enhance the absorption of heparin by controlling its release from this formulation as well as increasing the buccal-residence time and resistant to oral fluids. Besides, this delivery system has a negative charge with a mean diameter between 400 and 500 nm. It is worth to note that the drug-free nanoparticles were found to be accumulated in the mucus layer and the superficial layers of the upper epithelium with a penetration depth of only 25 µm, whereas the LMWHs-loaded nanoparticles were deposited in the deep layers of the buccal epithelium (down to 250 µm). Besides, a positive rheological synergism (enhancement the adhesion and viscosity) between the nanoparticles and mucin was demonstrated by the results of the calculation of the rheological synergism parameter. This implies that the mixture's actual viscosity was greater than the theoretical viscosity that was determined by adding the viscosities of the polymeric nanoparticles and mucin. In line, it was observed that the in vitro release of heparin from polymethacrylate nanoparticles was extremely minimal (only 6.3 ± 0.9% after 4 h), because the proportion of heparin that permeated was drastically limited by the electrostatic interaction. Notably, the patients may suffer potential mucosal irritation and systematic side effects such as nausea, vomiting, and diarrhea following administration of buccal heparin (Mouftah et al. 2016; Ortiz and Morales, 2020). In conclusion, the use of mucoadhesive nanoparticles for buccal administration could open new frontier for pharmaceutical drug delivery by prolonging the drug residence duration on the oral mucosa. This increases the concentration of heparin cargo at the absorption site and leading to improve bioavailability and efficacy.

Sublingual heparin delivery

The sublingual route is promising for drug delivery since it can provide short and fast-onset activity, promote accessibility, have low enzymatic activity, and inhibit the breakdown of macromolecular medicines caused by oral gastrointestinal absorption and first-pass hepatic metabolism. Despite its promise, the sublingual heparin delivery route has not been thoroughly evaluated for LMWHs (Fuller 1958; Litwins et al. 1951). For example, the efficacy of heparin potassium tablets has been assessed since 1959 in 21 participants by in vitro evaluation of lipolytic activity and via measurements of plasma heparin potassium levels. Among 3 of them, heparin potassium was moderately absorbed, and 6 patients were possibly trace absorption. While 12 of them had no evidence of absorption of sublingual given heparin potassium. This study found that oral heparin potassium pills are unsuccessful in 85% (18 out of 21) patients (Engelberg 1959). Additionally, the recent examinations raised doubt on the validity of the first claims regarding sublingual administration of heparins. Furthermore, the plasma of treated patients with 20,000 U of UFH coupled with ethylenediaminetetraacetic acid (EDTA) as penetration enhancers did not display any significant differences in bioactivity. The fluctuations observed in the previous data could perhaps be attributed to variations in the characteristics of heparin formulations, as well as the sensitivity and precision of the bioactivity evaluation approaches that utilized optical density over a period of time (Spudis et al. 1965). Likewise, the causes of this failure are very close to the biological and physiochemical barriers for buccal route. Furthermore, heparins should pass through about 30 to 40 cell lines before they could enter the first blood vessels in the lamina propria (a thin layer forming mucus membrane). The other factors that could also impact on the absorption of sublingual heparin are the probability of swallowing of tablets, limited absorption surface area, stability in saliva, and only suitable to deliver small doses (Shaftel and Selman 1959). The potential adverse effects for this route may involve potential mucosal irritation such as tongue numbness, changing in taste of food, and systematic side effects such as nausea, vomiting, and diarrhea (Srikanth et al. 2017). To conclude, the idea of generating an effective sublingual heparin seems to be challenging and required for more investigations to improve the bioavailability of sublingual heparin.

Oral heparin delivery

The most predominant class of oral anticoagulants today is vitamin K antagonists (warfarin or coumadin) which had been widely used for more than 50 years. However, warfarin had significant side effects, narrow therapeutic index, and severe drug-drug or food-drug interactions. Frequent monitoring is also required due to the non-predictable pharmacodynamics and inherent fluctuation in response over time (Albuloushi et al. 2022; Schrag et al. 2023). This might be inconvenient for the many patients who take this drug on a chronic basis. There is still a demand in health care settings for a long-term, safe, and easier-to-take oral anticoagulant rather than warfarin for both physicians and patients. An oral version of UFH was developed in response to this unmet need by utilizing a novel oral drug delivery method that permits poorly absorbed molecules to be absorbed through the gastrointestinal tract. The major benefits for oral heparins involve: (1) Administrated at a fixed dose twice or thrice daily without frequent coagulation monitoring or dose adjustments; and (2) Minimal drug-drug and food-drug interactions (Arbit et al. 2006). However, the biological and physiochemical barriers such as high molecular weight and negative charge of UFH and LMWHs are considered the major obstacles to formulate oral dosage forms from heparin as previously discussed in buccal and sublingual heparins (Horwitz et al. 1993; Schluter et al. 2014). To address the existing barriers for oral heparin delivery system, different formulation techniques have been used (Al Jbour 2022; Fang and Tang 2020). The following mechanisms were developed to overcome these challenges: (1) The permeabilization of cell membranes through the use of polycationic lipophilic-core dendrons (partial dendrimers) and bile salts derivatives; (2) Alteration of the tight-junction system by addition of absorption enhancers such as labrasol, sulfonated surfactants, EDTA, saponins, chitosan derivatives, carbopol 934P, sodium caprate, and Zonula occludens toxins synthetic peptide derivative AT1002; (3) Enhancing the lipophilicity of the drug by covalently attaching it to lipophilic molecules such as deoxycholic acid conjugates and dimethyl sulfoxide; as well as by using carriers (consisting of organic acids, sodium N-[10-(2-hydroxybenzoyl) amino] decanoate, sodium N-[8-(2-hydroxybenzoyl) amino] caprylate, diamine salt (ITF 1331 or counterion no. 4)), microemulsion formulations, polyion complex micelles, liposomes, and dendrons (Fig. 2); and (4) Preserving the drug formulation against the acidic pH of stomach using polymeric nanoparticles, alginate/chitosan/polyethylene glycol microparticles, and enteric coating dosage forms (Fang and Tang, 2020; Neves et al. 2016; Schluter et al. 2014). For example, the oral bioavailability of LMWHs was increased by 1.5% after it was conjugated with deoxycholic acid and loaded in a microemulsion system (Fang and Tang, 2020). In line, the results of in vivo pharmacokinetic study have demonstrated that the oral bioavailability of LMWHs (enoxaparin) was markedly improved about 6.8-fold after entrapped in lipid–polymer hybrid nanoparticles. Besides, its therapeutic efficacy against pulmonary thromboembolism was also enhanced 2.99-fold by lipid–polymer hybrid nanoparticles. This is due to the fact that these nanocarriers have excellent biocompatibility in the intestine (Tang et al. 2020). Notably, the major side effect for oral heparins involve bleeding complication and thrombocytopenia (low platelet counts) (Yan et al. 2020). To sum up, the oral heparin route continues to be safest, convenient, cost-effective, and encouraging the highest levels of patient compliance. Besides, further research is needed with oral UFH and LMWH especially in solid formulation. Table 1 outlines the main absorption studies that were conducted on various oral heparin formulations.

Fig. 2.

Illustration of the transport mechanism for oral heparin. The lipophilicity of heparin was enhanced after it associated with hydrophobic carriers via weak linkages. When the heparin and carrier enter the bloodstream, they separate through simple dilution (Arbit et al. 2006)

Table 1.

List of the available absorption studies for several oral heparin formulations

Heparin Types	methods of administration	Mechanisms of action	Summary of the main results	Reference
LMWH	Mixing with buffer solution (pH 4 and 7)	Unknown	Fluctuation and hard to measure the plasma levels for both pH 4 and 7 solutions following oral administration of LMWH	Dryjski et al. 1989
UFH	Dissolving in isotonic normal saline (0.9% w/v)	Exerting immune modulatory effect via interaction with cytokines	Reduction in the symptoms of rheumatoid arthritis	Imiela et al.1995
UFH	Taken with food (7 g of bread)	Modification on lipid metabolism	Significant reduction in triglyceride, and slight drop in cholesterol, HDL and LDL	Horwitz et al. 1993
UFH	Drinking with 200 mL of water	Expected by osmosis	Increment in the plasma level of anti-Xa efficacy after 5 min of administration, and maximum level achieved at 2 h	Hiebert et al. 2005

Rectal and vaginal heparin delivery

Rectal administration is a secondary option after oral and intravenous (IV) routes of drug administration and provides several benefits. These include retention of large volumes, rapid absorption of low molecular weight drugs, by-passing of the first-pass metabolism and controlled drug delivery. Besides, the other advantages are absorption into the lymphatic system, improved efficacy of localized treatment, enhanced absorption, and ability for administration of gastric unstable drugs (Ahmad et al. 2021). The vagina is another route that can effectively and safely deliver heparin. This could have clinical relevance not only for treating systemic thrombosis, but also for improving the pharmacotherapy of other localized disease conditions such as gynecological surgeries, septic pelvic thrombophlebitis (a serious endometritis complication), and in cases of postpartum ovarian vein thrombosis following vaginal delivery (Motlekar and Youan 2006; Witlin and Sibai 1995). However, the rectal and vaginal routes have been neglected due to the several delivery challenges such as inconsistent absorption, small absorption surface area, drug metabolism, privacy concerns, and poor patient adherence. Several methods have been studied to enhance the delivery of rectal heparin. The main aim for these approaches is to modify the permeability of cell membrane using sodium cholate, bile salts and sodium lauryl sarconsinate (Rathi et al. 2022). The animal studies have revealed that the heparin absorption is significantly influenced by the disruption of tight junctions. Additionally, the transport of heparin in the rectal membrane was further improved up to 20 times by co-administering mucolytic drugs and permeation enhancers as demonstrated in Table 2. This is due to the fact that when one approach alone is ineffective, such as in the case of inflammatory bowel disease, a mix of oral and rectal formulations should be used (Ahmad et al. 2021; Rathi et al. 2022). In conclusion, modified polymers with desirable characteristics are facilitating the development of novel rectal drug delivery systems. Addressing compatibility, toxicity, and control challenges with the rectal drug delivery system could make it a desirable therapeutic option for several diseases/disorders.

Table 2.

Overview of available in vivo studies on rectal absorption of heparins

In vivo models	Heparin types	Component of formulation	Mechanism of action	Summary of the main results	Reference
Rat	UFH	Oil and SLS (1–3 mg/kg)	Permeation enhancement activity of surfactant	Increased bioavailability by 20-times, exhibiting dose-dependent anticoagulant activity	Stanzani et al. 1981
Rodent	(35S) heparin	SC or SDC	Penetration promoting of SC and SDC	Improvement of the absorption by rectal mucosa with SDC only, and reduction in partial thromboplastin time (PTT) via SC	Ziv et al. 1983
Rat	LMWH	Micronized enema of SC (10–20 mg/mL)	Permeation potentiation activity of SC	Acceleration the absorption of LMWH by SC	Nissan et al. 2000

SC Sodium cholate, SDC Sodium deoxycholate

Transdermal heparin delivery

The skin offers a convenient and readily accessible route for drug delivery. The delivery of heparin via transdermal route is an attractive approach since the absorption of drugs through the skin bypasses the first-pass metabolism, and it can also be used to treat superficial venous thrombosis by binding to the keratinocytes (Arshad et al. 2021). This delivery system has several benefits over conventional routes. These include the potential for prolonged release of drugs and the reduction of irritation (Du et al. 2022; Vora et al. 2021). The main barrier for transdermal heparin delivery is the stratum corneum layer that can decrease the bioavailability of bioactive macromolecules through the skin. To solve this obstacle, various methods such as addition of penetration enhancers, liposomes, changing the skin partitioning coefficient, disruption of the lipid bilayer structure, replacement of bound water, delamination of the stratum corneum, phonophoresis (employing ultrasound waves), and electroporation (using a high current voltage to make pores in skin) (Zafar et al. 2021). Besides, iontophoresis (inducing heat via weak electrical current), needle free injections, and microfabricated microneedles were also used to facilitate the penetration of heparin via stratum corneum (Alyoussef Alkrad et al. 2023; Zafar et al. 2021; Zhai et al. 2021). These approaches were previously evaluated using several in vitro and in vivo models as summarized in Table 3. For example, Song et al. (2011) have found that the skin permeability and deposition of LMWHs were increased by 2.6-fold and 3.2-fold respectively after entrapping it in flexible liposomes compared with LMWHs alone. Transdermal route could cause allergic reaction such as some mild discomfort, redness, itching, or a rash (Song et al. 2011). In summary, parenteral route for the treatment of pulmonary embolism, venous thromboembolism, and cardiovascular events could potentially be replaced with LMWH transdermal loaded via liposomes.

Table 3.

The available in vitro and in vivo studies on absorption and permeation of transdermal heparins

Types of experimental model	Heparin types	Transdermal methods	Mechanism of action	Summary of the main results	References
In vitro human-derived epidermis tissues	UFH	High-voltage (100 V) pulses	Modification of ionic and molecular transmission process	Facilitating the transdermal penetration by high-voltage pulses	Weaver et al. 1997
In vitro rat skin	UFH	Electroporation for short time	Inducing pores in skin	Increased skin penetration up to 5-times	Vanbever et al. 1997
In vitro pig skin	LMWH	Low-frequency ultrasound waves	Ultrasonic mediated-transdermal permeation enhancement	Extending the levels of anti-factor Xa by 6% in the first day	Long et al. 2000
In vivo human skin	LMWH	Microneedles	Mechanical loosing/reduction in stratum corneum layer	Similar efficacy with usual medical needles; but with less pain	Hollingsworth et al. 2000
In vivo human skin	UFH	Liposomal spray gel	Reduction of skin inflammation	Synergistic action with compression therapy used for treatment of vein thrombosis	Katzenschlager et al. 2007

Pulmonary heparin delivery

Heparin sodium (for inhalation) was classified as an orphan drug by the European Commission in 2005 to treat cystic fibrosis. Nowadays, lung diseases such as bronchial asthma and asthma-induced airway hypersensitivity, pulmonary fibrosis, thromboembolism, and cystic fibrosis are being treated with inhaled heparin regimens (Dixon et al. 2021). The past in vivo studies have found that inhaled heparins can exert their antithrombotic and anti-inflammatory actions via several mechanisms such as suppression of inflammatory mediators, modulating the release of alveolar fibrin, inhibition of inositol triphosphate receptors, and modification of tight junction of epithelial cells (Table 4). The benefits of local delivery in the lungs are numerous. Initially, the local administration of heparin uses smaller doses which reduces side effects. Secondly, the application costs are decreased by reducing the number of doses through local administration. Third, the pulmonary route avoids the hepatic first-pass effect (Ahmed et al. 1992; Dixon et al. 2021; Liu et al. 2024). The lungs are also considered a favored site for drug delivery because of their extensive vascularization of the respiratory mucosa, wide absorption area, and comparatively minimal enzymatic activity. In accordance, the bioavailability of heparin was found to be similar or greater than subcutaneous injection (35–60%). However, the inhaled heparin (blood levels of male rats) was demonstrated to be faster than injection route (t_1/2 40 min for aerosols vs. 2.5 h for injection) with no side effect (Qi et al. 2004). In contrast, the excessive hydrophilicity and surface charges could prevent LMWHs from being absorbed from the respiratory tract. One of the other barriers in pulmonary drug delivery is ensuring that the drug is consistently positioned at the alveolar absorption site (Zieliński et al. 2019). Due to the significant attention has been received about this route, numerous devices that transport drugs consistently to the deep lung tissue have been designed and developed (Sibum et al. 2018; Yildiz-Pekoz et al. 2017). To enhance the pulmonary delivery of heparin, nano and microparticles were developed. Furthermore, they can reduce enzymatic degradation of heparin within the airway, potentiate the passive targeting into the lungs, and enable a long-lasting localized treatment. Despite this, these systems can also face the following issues: (1) The FDA has not approved the use of polymers such as poly-L-lactide-glycolic acid, poly (lactic acid), and chitosan to prepare heparin-loaded nano or microparticle systems for use in lung applications, and (2) The primary issue with formulation design is the stability of the liposomal and other nanoparticle formulations (Qi et al. 2004). In summary, the previous studies reveal that the effective non-invasive administration of LMWH and heparin especially could be developed if they loaded in the transporter devices and nano-formulations. The bioavailability of inhaled aerosolized heparin is similar to that of subcutaneous injection, making it a promising substitute for the treatment of chronic antithrombotic drugs and possibly other medical conditions as well.

Table 4.

In vivo evaluations of the delivery of heparins by pulmonary route

In vivo models	Heparin types	Pulmonary devices	Mechanism of action	Summary of the main results	References
Guinea pigs	LMWH and UFH	Ultrasonic nebulizer	Inhibition of inflammatory mediators	Exerting anti-allergic and reduction the inflammation of airways	Wang et al. 2000
Rabbit	UFH	Ultrasonic nebulizer with mask	Controlling the release of alveolar fibrin	Prevent lung fibrosis by decreasing the production of soluble collagen	Gunther et al. 2003
Sheep	UFH	Raindrop nebulizer	Suppression of inositol triphosphate receptors	Inhibition of antigen-induced bronchoconstriction	Ahmad et al. 1992
Rat	LMWH and UFH	Insufflator	Modification of tight junction of epithelial cells	Blockade of thrombosis and reduce the onset of action	Qi et al. 2004
Dog	UFH	Ultrasonic nebulizer	Anticoagulant effect	Direct relation between the dose and duration of effect. Unchanged adverse effect	Jaques et al. 1976

Nasal heparin delivery

Recently, this route was used to systematically deliver medications in cases of emergency. Besides, it can also be used to treat local diseases such as allergies. The most common nasal dosage forms used are nebulizers and solution vapor. Several advantages would be provided by an effective nasal heparin delivery system such as an immediate onset of action and prevention of hepatic first-pass metabolism (Ashmawy et al. 2023; Harris et al. 2022). For example, a total of 581 patients with asthma and COPD from 26 studies (participated in the qualitative analysis) and 16 studies were involved in the meta-analysis. Among these studies, treatment efficacy (improvement of lung function) was the main endpoint and determined by the standardized mean differences (SMD) of the forced expiratory volume per second (FEV1) expressed either as a percentage or as a per milliliter. Besides, the quality of evidence was evaluated by the grading of recommendations assessments, development, and evaluations (GRADE) approach. When compared to the control group, heparin significantly affects both FEV1% and FEV1 ml (SMD 2.7, 95% CI 1.00; 4.39; GRADE high, SMD 2.12, 95% CI − 1.49; 5.72: GRADE moderate, respectively). In terms of safety, inhaled heparin have shown a good coagulation profile and mild tolerable side effects (Ashmawy et al. 2023). However, the primary obstacles to the absorption of nasal heparin are the following: short nasal residence period, enzymatic degradation, drainage of heparin from nose if given at large volume, and the inability of nasal cavity to allow the passage of any substances larger than 1 kDa. The site of administration for heparin (anatomical factors) in the nose may also have an impact on nasal absorption. Furthermore, greater contact between this drug and the nasal mucosa occurs in the anterior region of the nose, while the mucociliary clearance mechanism of the nose quickly removes any drug applied to the posterior part of the nose. Reduction in the eosinophil production, activation of vagal nerve, and promoting the nasal were also found to be the main delivery mechanisms of nasal heparins (Carpenè et al. 2022; Sharma et al. 2021) (Table 5). In conclusion, prior studies indicate that the inhaled heparin and its derivatives may be beneficial in treating exacerbations of asthma or COPD and could be added in addition to the standard treatment. To attain the best clinical results for those patients, the appropriate heparin therapy dosage, timing, frequency, and duration should be taken into account. Additionally, further broad parallel RCTs involving children, people with COPD, and various types and stages of asthmatic patients are required. To recapitulate and better understanding, nasal route and other non-invasive delivery systems of heparins were summarized and compared with conventional parenteral heparin in Table 6.

Table 5.

Summary of the available in vivo studies on nasal delivery of heparins

In vivo models	Heparin types	Nasal methods	Mechanism of action	Summary of the main results	References
Rat	LMWH and UFH	Nasal dropper (containing 0.25% tetradecylmaltoside solution)	Enhanced nasal penetration	Improved the bioavailability of LMWH from 4 to 19%; whereas unchanged for UFH	Arnold et al. 2002
Human	UFH	Inhalation of solution vapor	Stimulation of vagal and anticoagulant effect	Reduction in heart rate and increased the onset of action	Uryvaev et al. 1997
Human	UFH	Nebula nebulizer	Decreasing the production of eosinophil	Declined in the nasal allergic reactions	Vancheri et al. 2001

Table 6.

The comparison between old and new heparin delivery systems

Heparin delivery systems	Advantages	Disadvantages/Barriers
Old or traditional parenteral heparin	-Widely available -Reasonable cost	-Invasive and less convince by patients -Higher adverse effects -Several manufacturing requirements such as pyrogen and particle free, isotonic, sterile, and stable -Pharmacokinetic and pharmacodynamic barriers such as enzymatic degradation by heparinase in the liver and intestinal microflora, chemical instability at acidic pH, and limited absorption by the epithelial and mucosal barriers -Desulfation and glycoside residue metabolism at the acidic pH of stomach if heparinase-derived heparin fragments are not included -Increase the risk of restenosis while using heparin stent-based therapy
Novel heparin delivery systems
Buccal	-Ease of administration -Rapid cellular recovery -Higher vascularization -Non-invasive and avoid of the first-pass metabolism and liver clearance	-The possibility of inadvertently ingesting the delivery device -Salivary scavenging -The barrier qualities of the buccal mucosa -Limited absorption in buccal mucosa for heparin due to its poor lipophilicity and high molecular size -Requirement for mucoadhesive nanoparticulate carriers, chemical permeation enhancers, enzyme inhibitors, and mucoadhesive materials with longer residence durations to increase the bioavailability and buccal absorption of heparin
Sublingual	-Good accessibility -Resistance of trauma -Prevention of the breakdown of macromolecular drugs caused by oral gastrointestinal absorption and first-pass hepatic metabolism	-Demand for higher penetration ability to pass through about 30 to 40 cell lines before entering the first blood vessels in the lamina propria (a thin layer forming mucus membrane)
Oral	-Wide therapeutic window, -Less requirements for monitoring -Lower adverse effects and interactions with drugs and food compared with warfarin	-Challenging to formulate the oral dosage forms from UFH and LMWHs due to the high molecular weight and negative charge of heparin
Rectal and Vaginal	-Safe route to deliver heparins -The ability to use in the treatment of localized and systemic thrombosis conditions, as well as for gynaecological surgery associated with thrombosis	-Highly affected by lower gastrointestinal diseases -Poor absorption and insufficient rectal/vaginal does may need for additional doses of oral heparin
Transdermal	-Bypassing the first-pass metabolism -Used to treat superficial venous thrombosis by binding to the keratinocytes -Prolonged release of drugs -Non-invasive	-Reduction the bioavailability of heparins through the skin due to thickness of stratum corneum layer -Requirements for penetration enhancers, nanoparticles, changing the skin partitioning coefficient, disruption of the lipid bilayer structure, replacement of bound water, delamination of the stratum corneum to facilitate the permeability and absorption of heparin
Pulmonary	-Ability to formulate heparin in smaller doses that will decrease the side effects and production costs -Avoiding the hepatic first-pass effect -Extensive vascularization of the respiratory mucosa -Wide absorption area -Minimal enzymatic activity -Reducible pharmacokinetics -Rapid action	-Poor pulmonary absorption for LMWH due to excessive hydrophilicity and surface charges of heparin -Cannot be used to deliver large amount of inhaled drugs -Demanding for numerous of pulmonary devices to transport drugs consistently to the deep lung tissue
Nasal	-Ability to use for treatment of local diseases such as allergies -Immediate onset of action -Prevention of hepatic first-pass metabolism -Rapid action	-Short nasal residence time -Enzymatic degradation -Drainage of heparin from nose if given at large volume, -The inability of nasal cavity to allow the passage of any substances larger than 1 kDa -Delivery of heparin is highly affected with the site of administration in the nose -Mucociliary clearance of any drug applied to the posterior part of the nose

The potential role of nanocarriers in improving heparin delivery

One remarkable feature of nanoparticles is their high degree of biocompatibility. Additionally, since the human body produces heparin in its mast cells, these nanoparticles could potentially be used in imaging (Ma et al. 2016; Yuk et al. 2011), bone and tissue engineering (Aslani et al. 2020; Barik et al. 2021; Yang et al. 2014), antimicrobial activity (Kemp et al. 2009), biosensing (Pathak et al. 2024), detection and treating diseases such as peripheral arterial disease (Meher et al. 2024; Noukeu et al. 2018;), and cancer (Hwang and Lee 2016; Li et al. 2010; Seib et al. 2016). Furthermore, heparin and its derivatives have the ability to interact and modify proteins that are involved in a variety of biological processes including angiogenesis, thrombosis, and inflammation. Besides, incorporation heparin with nanocarriers can also overcome the delivery barriers of this drug such as protection from degradation enzymes, enhancement the permeation from different cell membrane, and controlling its weight and charge (Rodriguez-Torres et al. 2018). Additionally, the other benefits may also include increasing the contact time and prolonging the release as well as improving the cell labelling and drug targeting (Zare et al. 2024). Furthermore, the strategies that have been developed to extend the release of heparin following subcutaneous or intravenous administration were found to be: (1) Encapsulation into targeted carriers such as nanoparticles, microparticles, hydrogels, and nanofibers; and (2) Adsorption onto cell surfaces and inorganic materials (Yang et al. 2022). Moreover, the polypseudorotaxane hydrogel based on complex of Tween 80 and α-cyclodextrin were also used to extend the release of LMWHs. For instance, this complex has several favorable properties for the formation of a drug-releasing depot after subcutaneous injection including biocompatibility, ease of injection, shear-thinning (the reduction of viscosity of fluid under shear strain), and thixotropic behavior (decreasing the viscosity of thick materials overtime after agitation) (Tang et al. 2022). In accordance, Fang et al. (2018) have found that the release of enoxaparin complexed with cationic polymer namely ε-polylysine, chitosan, was 30.39%, 39.52% and 22.18% within 144 h compared with 99.37% for enoxaparin solution hydrogel within same period of time (Fang et al. 2018).

These novel nanovesicles can be synthesized using chemical modification such as conjugation and cross-linking to create nano-biomaterials with specific functionality for a range of applications. For example, heparin has been used to synthesize metal nanoparticles such as silver (Huang and Yang 2004), gold (Guo and Yan 2008; Kim et al. 2013, 2004; Rodríguez-Torres et al. 2014), and metal oxide (Vismara et al. 2013) as well as magnetic particles (Wuang et al. 2006), poly(lactide-co-glycolide) complexes, and conjugates such as silica (Kuo and Shih 2009) and chitosan (Fan et al. 2024; Shahbazi et al. 2013; Shahbazi and Hamidi 2013) (Fig. 3). Likewise, the other nanoparticles that can also be used to deliver heparin include inorganic (Hoffart et al. 2002) and polymeric nanoparticles (Bae et al. 2018; Liang and Kiick 2014), nanofibers (Başaran et al. 2021; Hou et al. 2016; Wu et al. 2015), nanogels (Bae et al. 2008; Mei et al. 2016; Thi et al. 2024), micelle (Chen et al. 2015; Zhang et al. 2016), liposomes (Cao et al. 2021; van Solinge et al. 2023), and quantum dots (Li et al. 2015; Peng et al. 2015). For example, doxorubicin was encapsulated in an amphiphilic nanocarrier created by conjugating deoxycholic acid and heparin to treat squamous cell carcinoma (SCC) using a two-step process. Subsequently, these nanoparticles were evaluated for cytotoxicity, antitumor activity, and toxicity (to assess their safety as drug carriers). It was demonstrated that this conjugation had a high loading efficiency and release, with increased the anticancer activity of doxorubicin (Park et al. 2006). Additionally, Zhang et al. (2015) were also synthesized a promising system consisting of two chemotherapies: Doxorubicin and all trans retinoic acid (ATRA) (Zhang et al. 2015). The first anticancer drug is conjugated to LMWHs, while the ATRA is physically loaded. The main benefits of that work are that the anticancer activity against epithelial MCF-7 breast cancer cells of these drugs was significantly higher (3-folds) than that obtained for the free drug solutions (Zhang et al. 2015). In the other study, LMWHs was conjugated to stearyl amine to produce a polymer that was then used to formulate self-assembled nanoparticles to entrap docetaxel. This study has shown that the antiproliferative efficacy of docetaxel loaded in this formulation against MCF-7 and MDAMD 231 (human breast carcinoma cells) was increased and heparin maintained 30% of its anticoagulant effect (Park et al. 2006). In accordance with that, Yang and colleagues, (2016) have demonstrated that the entrapment of sorafenib loaded in chitosan/heparin Pluronic-coated nano-vehicles led to increase the anti-cancer activity of sorafenib (5-times) against BCG-823 cells (gastric cancer) compared with sorafenib solution (Yang et al. 2016).

Fig. 3.

The several types of nano-biomaterials used to deliver heparin. This can be done through chemical modification such as conjugation and cross-linking between heparin and nanocarrier molecules

Heparin nanomedicines were not only used in cancer, but they have been also applied to treat and diagnose diseases. For example, Chang et al. (2011) synthesized a polymeric mixture composed of heparin, chitosan, and berberine to treat Helicobacter pylori, a bacteria caused gastric and duodenal ulcers (Chang et al. 2011). The alkaloid berberine, derived from the barberry plant, is used to treat diarrhea, gastroenteritis, and suppress the H. pylori bacteria. Heparin was utilized in that work because it has an ability to bind with cell receptors and facilitate ulcer healing, whereas chitosan was used due to its biocompatibility and adhesion features (Chang et al. 2011). Besides, ciprofloxacin loaded genipin cross-linked chitosan/heparin nanoparticle system was also synthesized to target this antibiotic against enteropathogenic bacteria using a simulated gastrointestinal system (Kumar et al. 2016).

Discussion

To our knowledge, the first comprehensive study of different heparin delivery systems was published in 1964, which only discussed a limited number of routes of drug administration (Windsor and Freeman, 1964). It is also worth noting that the recent reviews mainly focus on the oral heparin delivery systems rather than the other promising non-invasive routes. Additionally, they also emphasize on the new indications for heparin without addressing the existing delivery obstacles of parenteral heparin. Instead, this review evaluates the traditional parenteral heparin along with all available non-invasive heparin delivery systems. Besides, the benefits, main barriers, possible solutions to enhance the delivery of heparin for each route were also covered in this study. Besides, this work also emphasizes the use of nanoparticles to address the heparin delivery-related barriers to improve the efficacy and safety of this drug. Notably, one limitation in this review is the inability to summarize, compare and critically analyze clinical and bioavailability data. The wide variations in operational practices are the cause of this limitation. For instance, there was significant variation in the kind and nature of heparin used in each trial, the different doses given, the animal species employed, the administration technique, the methodology for analyzing blood samples, and the procedures for gathering and using data.

Conclusion

Regardless the routes of administration for this drug, the successful and full treatment benefit of non-invasive delivery of heparin are mainly relying on the overcoming the biological, biophysical, and biochemical barriers for each route of administration. This can be achieved by using several methods such as changing the physiochemical properties of drug, enhancing penetration at the site of action, adding permeation enhancers, and delivering using nanocarriers. More in vivo and clinical studies are needed before the non-invasive heparin products can be available on the market and utilized in clinical settings.

Abbreviations

AT

Antithrombin

ATRA

All trans retinoic acid

Da

Dalton unit

EDTA

Ethylenediamine tetra acetic acid

GRADE

Grading of recommendations assessments, development, and, evaluations

LMWHs

Fractionated low-molecular-weight heparins

MW

Molecular weight

SCC

Squamous cell carcinoma

U

Dalton unit

UFH

Unfractionated heparin

SC

Sodium cholate

SDC

Sodium deoxycholate

SMD

Standardized mean differences

Author contribution

Conceptualization; validation; formal analysis; investigation; writing—original draft preparation; writing—review and editing; project administration; and funding acquisition were all performed by single author [MA].

Funding

No funding was received for conducting this study.

Data availability

The data that support the findings of this study are available from the corresponding author, upon request.

Declarations

Ethical approval

This article does not contain any studies with human participants or animals performed by the author.

Competing interests

The author confirms that there is no conflict of interest related to the manuscript.