Sugammadex: A revolutionary drug in neuromuscular pharmacology

Abstract

Sugammadex (ORG 25969) is a unique neuromuscular reversal drug; a novel cyclodextrin, the first in a new class of selective relaxant binding agents, which reverse neuromuscular blockade (NMB) with the aminosteroid non-depolarizing muscle relaxants rocuronium and vecuronium. Sugammadex can reverse moderate or deep NMB. The clinical use of sugammadex promises to eliminate many of the shortcomings in current anesthetic practice with regard to antagonism of rocuronium and other aminosteroid muscle relaxants.

INTRODUCTION

Muscle relaxants are used during intraoperative period to facilitate endotracheal intubation, ensure patient immobility and improve surgical exposure.[1] Reversal agents are used to terminate the action of muscle relaxants. The ideal reversal agent should have a fast onset; should be efficient at any time, even soon after paralyzing the patient; it should be able to provide complete reversal either for light or profound blockade; it should have a longer half-life than the muscle relaxants and it should not have any side-effects. The ideal reversal agent is yet to be found, but sugammadex is very close to being an ideal reversal agent.[2] Sugammadex is a synthetic cyclodextrin molecule, which acts by encapsulation of rocuronium.[3,4,5,6] The discovery of encapsulation for reversal of aminosteroid muscle relaxants is the result of work done by Bom, a research scientist at Organon International (Oss, Netherlands).[7,8,9] Literature search for the article was carried out using Google Scholar, Proquest database and on wikepedia using the term “Sugammadex.”

CHEMICAL STRUCTURE

Sugammadex [6A,6B,6C,6D,6E,6F,6G,6H-octakis-S-(2-carboxyethyl)-6A,6B,6C,6D,6E,6F,6G,6H-octathio-γ-cyclodextrin octasodium salt] is a modified γ-cyclodextrin [Figure 1]. Chemical formula is C₇₂H₁₀₄Na₈O₄₈S_8. “Su” stands for sugar and “gammadex” stands for structural molecule gamma-cyclodextrin.[1] Cyclodextrins are cyclic dextrose units joined through 1-4 glycosyl bonds that are produced from starch or starch derivates using cyclodextrin glycosyltransferase. The three natural unmodified cyclodextrins are α-, β-or γ-cyclodextrin. Compared with α-and β-cyclodextrins, γ-cyclodextrin exhibits more favorable properties in terms of the size of its internal cavity, water solubility and bioavailability. To have a better fit of the larger rigid structure of the aminosteroid muscle relaxant molecule (e.g., rocuronium or vecuronium) within the cavity of γ-cyclodextrin, the latter was modified by adding eight side chains to extend the cavity. This modification allowed the four hydrophobic steroidal rings of rocuronium to be better accommodated within the hydrophobic cavity. In addition, adding negatively charged carboxyl groups at the end of the eight side chains served two purposes. First, the repellent forces of the negative charges keep propionic acid side chains from being disordered, thereby allowing the cavity to remain open and maintain structural integrity. Second, adding these negatively charged carboxyl groups enhances electrostatic binding to the positively charged quaternary nitrogen of rocuronium [Figure 1]. Three-dimensional structure resembles a hollow, truncated cone or a doughnut.[9]

Figure 1.

Structure of sugammadex

Mechanism of action

Inactivates rocuronium by encapsulating (chelating) the free molecule to form a stable complex.[10] The structure has a hydrophobic cavity and a hydrophilic exterior because of the presence of polar hydroxyl groups. Hydrophobic interactions trap the drug into the cyclodextrin cavity, resulting in the formation of a water-soluble guest–host complex. Sugammadex exerts its effect by forming very tight complexes at a 1:1 ratio with aminosteroid muscle relaxants (rocuronium > vecuronium >> pancuronium).[9,10,11,12] The intermolecular (van der Waals’) forces, thermodynamic (hydrogen) bonds and hydrophobic interactions make the sugammadex–rocuronium complex very tight. The sugammadex–rocuronium complex has a very high association rate (an association constant of 107 M-1) and a very low dissociation rate. It is estimated that, for every 25 million sugammadex–rocuronium complexes, only one complex dissociates. The resulting reduction in free rocuronium plasma concentration creates a gradient between the tissue compartment (including the NMJ) and plasma; free rocuronium moves from tissue to plasma, with a reduction in nicotinic receptor occupancy at the NMJ.[10,13,14]

Distribution

The volume of distribution of sugammadex is approximately 18 L and volume of distribution at steady state is 11-14 L (0.16-0.20 L/kg). The drug does not bind to plasma proteins or red blood cells.[2]

Metabolism and elimination

The drug does not produce any metabolites and is mostly excreted through urine in the unchanged form within 24 h. An insignificant part is excreted through feces or in expired air (0.02%). The plasma clearance of the drug ranges from 84 to 138 ml/min.[2]

Dosage and formulation

Table 1.

Recommended dosage of sugammadex

Minimum effective reversal dose: 2 mg/kg IV.[12]

Administration: The drug should be given as a single IV bolus, delivered within 10 s.[13]

The drug is available in IV formulation only; vials of 200 mg (2 ml) or 500 mg (5 ml) and is for non-refrigerated storage.[19] The drug was originally designated as Org 25,969. Trade name is Bridion. Sugammadex was discovered at the Newhouse research site in Scotland. Scientists who discovered Sugammadex worked for the pharmaceutical company, Organon. Organon was acquired by Schering-Plough in 2007; Schering-Plough merged with Merck in 2009. Sugammadex is now owned and sold by Merck. On January 3, 2008, Schering-Plough submitted a New Drug Application to the US FDA for sugammadex, but was rejected on August 2008.[20,21] It was approved for use in the European Union on July 29, 2008.[17] The drug is also approved for use in Australia, Iceland, New Zealand and Norway.

Indication

Reversal of neuromuscular blockade (NMB) in the operation theater and in the intensive care unit (ICU).[17]

Drug interactions

Toremifene, a chemotherapeutic drug, which is a selective estrogen receptor modulator, can delay the reversal by displacing the formation of the rocuronium-sugammadex complex. The drug can theoretically bind with contraceptive steroids. As endogenous steroids and steroidal drugs lack the quaternary nitrogen of the aminosteroid muscle relaxants, they show a much lower affinity. Rocuronium-sugammadex complex can also be displaced by fusidic acid or high doses of flucloxacillin. Drugs like magnesium, aminoglycosides potentiate muscle relaxants; to counteract these effects, a larger dose of sugammadex may be required. Among anesthetic drugs the highest affinity constant was observed with remifentanil (0.2% of the affinity constant of sugammadex with rocuronium); it has not been shown to be clinically significant. Physical incompatibility has been reported with verapamil, ondansetron and ranitidine. Further investigations are required to assess other possible drug interactions.[1,2,9]

Sugammadex does not alter laboratory tests in general, but some modification of the serum progesterone assay and of the coagulation parameters like activated partial thromboplastin time, prothrombin time, INR has been noticed.[17]

Contraindications

Hypersensitivity to sugammadex or to any excipients.[13]

Special considerations

Patients with severe renal impairment: Clearance of the drug is reduced in patients with creatinine clearance below 30 ml/min. The efficacy of the drug is not reduced in these patients.[22] There are conflicting reports of its safety in these subset of patients; hence, it is recommended to avoid its use in such patients.[2]

Patients with hepatic impairment: Sugammadex-rocuronium complex is not eliminated by hepatic metabolism; therefore, hepatic impairment does not affect its excretion. However, it is advised to be cautious regarding its use in these patients.[2]

Obese patients: Use adult dose based on actual body weight.

Patients in ICU: Sugammadex has not been investigated in patients receiving rocuronium or vecuronium in the ICU.

Elderly: Use adult dose although recovery times are slower.

Pediatric patients: Pharmacokinetic profile is quite similar to that of adults. There is no clinical trial in children below 2 years of age.

Pregnancy and lactation: Caution in pregnant women. Sugammadex can be used during lactation.

Sex, race and body weight: They have no effect on the use of sugammadex.

Recurarization

A phenomenon of recurrence of NMB may occur where the reversal agents wear off before a muscle relaxant is completely cleared. It has been demonstrated to occur only rarely with sugammadex and only when insufficient doses were administered. The underlying mechanism is thought to be related to redistribution of relaxant after reversal. It may occur for a limited range of sugammadex doses, which are sufficient for complex formation with relaxant in the central compartment, but insufficient for additional relaxant returning to the central compartment from peripheral compartments.[16,17,18,19]

COMPARISON WITH NEOSTIGMINE

Sugammadex acts by encapsulation of rocuronium, whereas neostigmine is an anticholinesterase. Neostigmine has a ceiling effect and when given at a deep level of NMB, can result in inadequate reversal. Neostigmine is also associated with adverse effects like autonomic disturbances including bradycardia, which can be particularly troublesome during extubation in patients for cardiothoracic surgery, nausea and vomiting; these adverse effects are not noticed with sugammadex.[9,15,18,23,24,25]

LIMITATIONS

The drug is expensive. The cost of reversal of NMB with sugammadex in a 75 kg person is £59.74 for 2 mg/kg, £119.28 for 4 mg/kg and £357.84 for 16 mg/kg compared to £0.71 for spontaneous recovery from suxamethonium.[26] However, studies have shown that use of sugammadex can be cost-effective by reduced incidence of post-operative residual paralysis reducing operative time, post-operative recovery stay and also decreased side-effects associated with the use of suxamethonium.

Adverse effects

Sugammadex is a well-tolerated and relatively free of adverse effects. Some of the adverse reported in some of the trials are dysgeusia (metal or bitter taste) mainly seen after doses of 32 mg/kg or higher, recurrence of block, movement of limbs or body or coughing during anesthesia, coughing, grimacing or suckling on the endotracheal tube, procedural hypotension.[17,27,28]

Precautions

If re-administration of rocuronium or vecuronium is required a waiting time of 24 h is recommended. If NMB is required before the recommended waiting time has passed, a non-steroidal muscle relaxant should be used. Sugammadex should not be used to reverse block induced by non-steroidal blockers such as suxamethonium or benzylisoquinolinium compounds (because it cannot form inclusion complexes with these drugs) or aminosteroid muscle relaxants other than rocuronium or vecuronium.[9,16]

ADVANTAGES

1. Use of sugammadex will decrease the incidence of residual muscle paralysis and hence improve patient safety[29]

2. Anesthesiologists will not hesitate to give incremental doses of muscle relaxant if required towards the end of surgery

3. High dose rocuronium for rapid sequence induction, i.e., 1.2 mg/kg can be used safely in cases of short duration.

4. In case of need to rapidly terminate the effect of muscle relaxants, i.e., in cannot intubate cannot ventilate scenario, rocuronium would be preferred to suxamethonium

5. No additional anticholinestrases or anticholinergics would be needed for reversal of residual NMB, thus avoiding unwanted cardiovascular effects and other adverse effects of the drugs.[24]

WILL SUGAMMADEX BRING A FINAL DEMISE OF SUXAMETHONIUM?

Use of suxamethonium has declined in modern anesthetic practice. Suxamethonium has numerous adverse effects such as fasciculations, myalgia, hyperkalemia, heart rate changes and increased intragastric and intraocular pressures, malignant hyperthermia. Use of suxamethonium in children is not preferred due to the danger of hyperkalemic cardiac arrest in children with unrecognized muscular dystrophy.[30]

Suxamethonium is still used in difficult airway scenario, full stomach and in cases under general anesthesia of short duration. If sugammadex becomes widely available, rocuronium can be used as a better alternative in the above situations.

POTENTIAL IMPACT OF SUGAMMADEX ON DAY TO DAY ANESTHETIC PRACTICE

1. Sugammadex cannot reverse NMB with benzylisoquinolinium group of muscle relaxants or with suxamethonium

2. After sugammadex administration, reblock with rocuronium will be difficult and the dose required will be unpredictable. Benzylisoquinolinium group of muscle relaxants or suxamethonium should be used in such a scenario

3. Sugammadex does not have equal affinity with all aminosteroid relaxants. Reversal of pancuronium will require large doses of sugammadex

4. It is necessary to know the extent of NMB before sugammadex administration. Train of four (TOF) count or post tetanic count (PTC) may be sufficient to decide the dosage of sugammadex. Reversal of profound block with inadequate doses of sugammadex will result in incomplete reversal. TOF ratio will give an objective assessment to help determine if antagonism of residual block is actually required.[31,32]

CONCLUSION

Sugammadex may potentially promote the increased use of non-depolarizing aminosteroid muscle relaxants, but economic constraints may prevent its wide spread use and poses great limitations to its use.[33] It will prove useful for very short surgeries when an intermediate acting NMB is used or when the dose, timing or administration of neostigmine is inadequate. Surgeons should no longer encounter inadequate muscle relaxation and anesthesiologists should no longer encounter patients whose NMB is difficult to reverse at the end of surgery.[34] It should eliminate the occurrence of postoperative residual NMB. Assurance of no residual paralysis may enable anesthesiologists to better evaluate the success or failure when attempting to wean and extubate patients who have received aminosteroid muscle relaxants. Side-effects like nausea/vomiting or unwanted autonomic adverse effects encountered with neostigmine will be eliminated.[35] Improvements in patient outcome must have a dollar value that offsets the cost of the drug. FDA has still not approved the use of sugammadex due to some concerns regarding allergic reactions. The drug is being extensively used in the EU and Australia at present. Sugammadex should not replace good clinical practice titration of muscle relaxants to clinical needs and objective monitoring of NMB in the OT or ICU.[36] The introduction of propofol two decades ago changed anesthetic practice, no other drug has had the same impact. Undoubtedly, sugammadex is a milestone and is likely to change the face of clinical neuromuscular pharmacology.