A Comparison of Biological Therapies vs Traditional Immunosuppressant in the Management of Inflammatory Bowel Diseases: A Narrative Review

Abstract

Inflammatory bowel disease (IBD), encompassing Crohn’s disease and ulcerative colitis, is a chronic immune-mediated condition requiring long-term management. Traditional immunosuppressants, such as corticosteroids, thiopurines, and methotrexate, have been widely used but are associated with broad immunosuppressive effects and significant adverse events. The advent of biological therapies, including tumor necrosis factor (TNF) inhibitors, integrin inhibitors, and interleukin (IL)-12/23 inhibitors, has revolutionized IBD treatment by offering targeted immune modulation. Biologics have demonstrated superior efficacy in achieving and maintaining remission compared to traditional immunosuppressants, particularly in moderate to severe IBD. They provide targeted immune suppression, reducing systemic side effects, but are associated with risks such as infections, immunogenicity, and high costs. Traditional immunosuppressants remain relevant for milder cases and as combination therapy but are limited by delayed onset of action and toxicity concerns. Despite these advances, challenges such as treatment accessibility, high costs, and loss of response persist. The introduction of biosimilars and novel small-molecule drugs may improve treatment affordability, while personalized medicine approaches, including biomarker-driven therapy selection and therapeutic drug monitoring, are emerging as crucial strategies to optimize treatment outcomes. While biological therapies have transformed IBD management, future research should focus on refining treatment strategies, improving long-term safety, and enhancing accessibility to ensure better patient outcomes.

1. Introduction

Inflammatory bowel diseases (IBD), comprising Crohn’s disease (CD) and ulcerative colitis (UC), are chronic, relapsing-remitting disorders characterized by immune-mediated inflammation of the gastrointestinal tract.1 The pathogenesis of IBD involves a complex interplay of genetic susceptibility, environmental factors, gut microbiota, and dysregulated immune responses.2 Traditionally, immunosuppressants such as corticosteroids, thiopurines (azathioprine, 6-mercaptopurine), and methotrexate have been the cornerstone of IBD management.3 These agents help control inflammation by broadly suppressing immune activity but are associated with significant adverse effects, including increased risk of infections, malignancy, and drug-related toxicities. Despite their efficacy in inducing and maintaining remission, their long-term use is limited by safety concerns and variable patient response.4

The advent of biological therapies has revolutionized the management of IBD by offering targeted mechanisms of action with potentially improved safety and efficacy profiles. Biologic agents, including tumor necrosis factor (TNF) inhibitors (e.g., infliximab, adalimumab), integrin inhibitors (e.g., vedolizumab), and interleukin inhibitors (e.g., ustekinumab), selectively modulate specific pathways in the inflammatory cascade.5 Unlike traditional immunosuppressants, which exert broad immunosuppressive effects, biologics offer a more precise approach by blocking key cytokines or cellular interactions responsible for intestinal inflammation.6 This targeted strategy has led to higher rates of mucosal healing, reduced corticosteroid dependence, and improved quality of life for many patients. However, biologics are not without drawbacks, including high costs, the need for parenteral administration, and the potential for immunogenicity leading to loss of response over time.7

The choice between biological therapies and traditional immunosuppressants depends on disease severity, patient-specific factors, and therapeutic goals. While biologics have transformed treatment paradigms, traditional immunosuppressants continue to play a role in certain patient populations, particularly in combination therapy to enhance biologic efficacy.8 This review aims to provide a comparative analysis of biological therapies and traditional immunosuppressants in IBD management, highlighting their mechanisms, efficacy, safety profiles, and clinical applications. Understanding the strengths and limitations of each approach is essential for optimizing treatment strategies and improving patient outcomes.

2. Discussion

The management of inflammatory bowel disease (IBD) has evolved with the introduction of biological therapies, which offer targeted immunomodulation compared to the broader immunosuppressive effects of traditional agents.9 While both strategies aim to control inflammation, prevent complications, and improve patients’ quality of life, they differ significantly in their mechanisms of action, efficacy, safety profiles, and long-term outcomes. A direct comparison of biological therapies and traditional immunosuppressant is crucial for optimizing treatment strategies in IBD patients.10 Fig. 1 demonstrates a structured stepwise treatment flowchart for inflammatory bowel disease (IBD).

Fig. 1.

Stepwise treatment for inflammatory bowel disease (IBD).

2.1. Mechanism of action: broad vs. targeted immunosuppression

Traditional immunosuppressant, including corticosteroids, thiopurines (azathioprine and 6-mercaptopurine), and methotrexate, work by broadly suppressing immune activity. Corticosteroids inhibit multiple inflammatory pathways by reducing cytokine production and immune cell activation, while thiopurines and methotrexate interfere with DNA synthesis, leading to reduced proliferation of immune cells.11 These agents lack specificity, affecting not only the inflammatory response in the gut but also systemic immune function.12 The stepwise escalation strategy in IBD management is illustrated in Fig. 1, outlining the transition from traditional immunosuppressants to biologics based on disease severity and treatment response.

In contrast, biological therapies offer a more selective approach by targeting specific components of the immune system. Tumor necrosis factor-alpha (TNF-α) inhibitors such as infliximab, adalimumab, and certolizumab pegol block the pro-inflammatory cytokine TNF-α, which plays a central role in the pathogenesis of IBD.13 More recently, integrin inhibitors like vedolizumab selectively inhibit gutspecific lymphocyte trafficking, thereby reducing systemic immunosuppression.14 Similarly, interleukin (IL)-12/23 inhibitors, such as ustekinumab, modulate the immune response by blocking cytokines involved in T-cell activation. The specificity of biologics provides a theoretical advantage by minimizing off-target effects and reducing the risk of systemic immunosuppression-related complications.15

2.2. Efficacy in induction and maintenance of remission

Clinical trials and real-world data have demonstrated that biologics generally achieve higher rates of sustained remission compared to traditional immunosuppressants, particularly in patients with moderate to severe disease.16 The SONIC trial, a pivotal study in Crohn’s disease, found that combination therapy with infliximab and azathioprine led to significantly higher rates of corticosteroid-free remission compared to either monotherapy.17 Similarly, vedolizumab and ustekinumab have been shown to be superior to placebo in maintaining remission in both Crohn’s disease and ulcerative colitis, with durable responses over time.18

Traditional immunosuppressants, on the other hand, are more effective in milder cases of IBD or as adjunct therapy. Thiopurines have demonstrated efficacy in maintaining remission but are less effective for inducing remission, often requiring several months for their full therapeutic effect.19 Corticosteroids are highly effective for induction therapy but are not recommended for long-term maintenance due to their adverse effects.20 Methotrexate, while useful in steroid-dependent Crohn’s disease, has limited evidence in ulcerative colitis and is often used as a second-line agent.21

Despite their advantages, biologics are not universally effective, and up to 30–40 % of patients experience primary non-response, while others develop secondary loss of response over time due to immunogenicity or mechanistic escape. In such cases, therapeutic drug monitoring and switching within or across biologic classes are necessary.22

2.3. Safety and adverse effect profile

One of the major limitations of traditional immunosuppressants is their association with significant long-term toxicities. Corticosteroids, despite their rapid efficacy, cause metabolic complications such as osteoporosis, diabetes, and adrenal suppression, making them unsuitable for long-term use.23 Thiopurines increase the risk of infections, bone marrow suppression, hepatotoxicity, and malignancies, including lymphoma and non-melanoma skin cancers.24 Methotrexate is associated with hepatotoxicity, pulmonary toxicity, and teratogenicity, limiting its use in certain populations.25

Biological therapies, although generally considered safer in terms of long-term complications, are not without risks. TNF inhibitors, for example, are associated with an increased risk of infections, tuberculosis reactivation, and paradoxical autoimmune conditions such as psoriasis or lupus-like syndromes.26 Additionally, their immunogenic nature may lead to the development of anti-drug antibodies, reducing efficacy over time. Integrin inhibitors like vedolizumab have a more favorable safety profile, with lower infection risks, though rare cases of progressive multifocal leukoencephalopathy (PML) have been reported with natalizumab, a related drug used in multiple sclerosis.27

The overall safety of biologics has led to their preference over traditional immunosuppressants in many treatment guidelines, especially for patients at higher risk of steroid dependence or immunosuppressant-related toxicities. However, long-term surveillance studies are still needed to assess their impact on malignancy risk and immune function over decades of use.28

2.4. Cost, accessibility, and healthcare utilization

One of the primary barriers to the widespread use of biological therapies is their high cost compared to traditional immunosuppressants. The development of biosimilars—biologic agents that are highly similar but more cost-effective than their reference biologics—has helped reduce costs in some regions, but financial constraints still limit access, especially in low- and middle-income countries.29 In contrast, thiopurines and methotrexate are widely available and inexpensive, making them a more feasible option in resource-limited settings.30

Many healthcare systems implement step therapy, requiring patients to fail conventional therapies before gaining approval for biologics. This delay can prolong disease activity, leading to complications such as strictures, fistulas, and the need for surgery.31 Increasing awareness and revising healthcare policies to allow earlier access to biologics in high-risk patients may improve long-term outcomes and reduce healthcare costs associated with hospitalizations and surgeries.32

3. Combination therapy: optimizing outcomes

Given the limitations of both biologics and traditional immunosuppressants, combination therapy has been explored as a strategy to enhance efficacy. The combination of TNF inhibitors with thiopurines has been shown to improve drug persistence and reduce immunogenicity.33 However, this approach also increases the risk of adverse effects, particularly infections and malignancies, necessitating careful patient selection. A detailed comparison between biological therapies and traditional immunosuppressants is presented in Table 1, summarizing their differences in mechanism of action, efficacy, safety, and accessibility.

Table 1.

Comparison of biological therapies and traditional immunosuppressants in IBD management.

Category	Biological Therapies	Traditional Immunosuppressants
Mechanism of Action	Targeted inhibition of inflammatory pathways (e.g., TNF-α, IL-12/23, integrins)	Broad immunosuppression via general immune cell inhibition
Examples	TNF inhibitors (infliximab, adalimumab), Integrin inhibitors (vedolizumab), IL-12/23 inhibitors (ustekinumab), JAK inhibitors (tofacitinib, upadacitinib)	Corticosteroids (prednisone, budesonide), Thiopurines (azathioprine, 6-MP), Methotrexate
Efficacy	Higher rates of mucosal healing, sustained remission in moderate to severe IBD	Effective for induction but less reliable for long-term maintenance
Onset of Action	Variable: TNF inhibitors (2–6 weeks), IL inhibitors (4–8 weeks), Integrin inhibitors (8–12 weeks)	Corticosteroids: Rapid (days to weeks), Thiopurines: Delayed (8–12 weeks), Methotrexate: Intermediate (4–8 weeks)
Duration of Use	Long-term maintenance therapy	Corticosteroids: Short-term only; Thiopurines & Methotrexate: Long-term use possible
Immunogenicity	Anti-drug antibody formation may lead to secondary loss of response	No immunogenicity, but potential cumulative toxicity
Adverse Effects	Increased risk of infections (e.g., TB, fungal, viral), malignancy concerns (rare), immunogenicity	Corticosteroids: Osteoporosis, diabetes, adrenal suppression; Thiopurines: Hepatotoxicity, myelosuppression, lymphoma risk; Methotrexate: Hepatotoxicity, teratogenicity
Combination Therapy	Often combined with thiopurines to reduce immunogenicity (e.g., infliximab + azathioprine)	Used in combination (e.g., thiopurines + methotrexate) but with higher toxicity risks
Monitoring Requirements	Therapeutic drug monitoring (TDM) for optimal drug levels and to prevent immunogenicity	Regular blood monitoring for hepatotoxicity, bone marrow suppression
Risk of Opportunistic Infections	Moderate to high (TNF inhibitors > IL-12/23 inhibitors > integrin inhibitors)	Moderate (higher with thiopurines and methotrexate)
Cost	High; limited access in resource-constrained settings	Lower cost; widely accessible
Availability	Requires special storage and administration (IV, SC)	Oral and widely available
Route of Administration	Intravenous (IV) or subcutaneous (SC) injections	Oral (thiopurines, methotrexate), IV (steroid pulses, methotrexate)
Long-term Safety	Generally better for non-TNF biologics but long-term risks (e.g., malignancy) still being studied	Cumulative toxicity limits prolonged use
Treatment Failure	Primary non-response (30–40 %), secondary loss of response common due to immunogenicity	Less common primary failure but more long-term toxicity-related discontinuations
Step Therapy Requirement	Often restricted by insurance, requiring failure of conventional therapy first	First-line in many guidelines due to lower cost and accessibility
Emerging Alternatives	JAK inhibitors (oral, rapid onset), S1P modulators (gut-selective)	Use of biosimilars to reduce costs
Preferred Patient Profile	Moderate to severe IBD, steroid-dependent or refractory cases, high-risk patients	Mild to moderate IBD, steroid-sparing maintenance in select cases

Newer treatment paradigms focus on sequential or combination strategies that balance efficacy and safety. For example, some patients may benefit from an initial course of a traditional immunosuppressant to control inflammation, followed by maintenance with a biologic.34 Therapeutic drug monitoring and personalized medicine approaches, such as biomarker-based treatment selection, are increasingly being incorporated to optimize response rates.35 Non-pharmacological approaches such as diet, lifestyle modification, surgery, and psychological support play supportive roles, but pharmacotherapy remains essential for controlling inflammation and preventing disease progression in IBD.37

The comparison between biological therapies and traditional immunosuppressants in IBD management requires consideration across several domains. Fundamentally, these therapies differ in their mechanisms of action: while traditional immunosuppressants exert broad immune suppression, biologics provide targeted inhibition of specific inflammatory pathways. This mechanistic difference directly translates into their efficacy, as biologics have been shown to induce and maintain remission more effectively in moderate to severe IBD, whereas conventional agents retain value in milder disease or as adjuncts. Safety profiles also diverge, with traditional agents associated with cumulative toxicities such as hepatotoxicity, myelosuppression, and malignancy, while biologics carry risks of infections, immunogenicity, and rare autoimmune complications.

Patient selection and disease context further influence therapeutic decisions. Biologics are generally preferred in patients with refractory, steroid-dependent, or high-risk disease, but their high costs, parenteral administration, and insurance-related step therapy requirements often restrict accessibility. Traditional immunosuppressants, by contrast, are inexpensive, widely available, and therefore remain important, particularly in resource-limited settings. Combination strategies, such as the use of infliximab with azathioprine, demonstrate improved remission rates and reduced immunogenicity but must be weighed against the heightened risk of infection and malignancy. Looking to the future, emerging therapies—including JAK inhibitors, S1P modulators, and novel biologics—offer new opportunities to overcome current challenges, especially when coupled with biomarker-driven personalized medicine approaches. Nonetheless, existing evidence is limited by strict trial populations, variable real-world responses, and incomplete long-term safety data, underscoring the need for further research to refine treatment strategies and optimize patient outcomes.

The therapeutic landscape of inflammatory bowel disease (IBD) has shifted considerably over the past decades, evolving from conventional immunosuppressants to more advanced biologic therapies. Conventional treatments, including corticosteroids, thiopurines, methotrexate, and mesalamine, remain foundational, particularly for mild to moderate disease, given their affordability and accessibility. Mesalamine, for example, continues to serve as a first-line treatment in ulcerative colitis, while corticosteroids are highly effective in inducing remission but are unsuitable for long-term use due to toxicity risks.39 Immunosuppressants such as azathioprine, 6-mercaptopurine, and methotrexate have proven utility in maintaining remission, but their efficacy is often limited by delayed onset of action and cumulative toxicities.40

The advent of biologic therapies, however, has transformed treatment paradigms, especially for moderate to severe IBD. Tumor necrosis factor (TNF) antagonists, integrin inhibitors, and interleukin blockers provide targeted suppression of specific immune pathways, demonstrating superior efficacy in achieving mucosal healing and sustained remission compared to conventional immunosuppressants. 41 Meta-analyses comparing biologics and immunosuppressants confirm that biologics not only improve remission rates but also reduce corticosteroid dependence and long-term complications in Crohn’s disease and ulcerative colitis.42 Nevertheless, biologics are not universally effective, with up to 40 % of patients experiencing primary non-response or secondary loss of response due to immunogenicity.43

Safety remains a critical factor in therapeutic selection. Immunosuppressants are associated with significant risks, including hepatotoxicity, bone marrow suppression, and malignancies such as lymphoma and non-melanoma skin cancers.44 By contrast, biologics carry risks of infections, tuberculosis reactivation, and paradoxical immune-mediated conditions, though integrin inhibitors such as vedolizumab are considered safer in terms of systemic immunosuppression.45 Comparative safety analyses suggest that while biologics and immunosuppressants both increase infection risk, biologics generally demonstrate a more favorable long-term safety profile, particularly when non-TNF agents are considered.46

Despite these advantages, cost and accessibility remain major barriers to biologic use, especially in low- and middle-income countries. Conventional therapies continue to play a crucial role where healthcare resources are constrained, and stepwise therapy policies often mandate their use before biologics are approved.47 The introduction of biosimilars has somewhat alleviated cost concerns, expanding access in certain regions, but disparities remain.48 Looking ahead, emerging small molecules such as Janus kinase (JAK) inhibitors and sphingosine-1-phosphate (S1P) modulators, as well as next-generation biologics like selective IL-23 inhibitors, are expected to broaden therapeutic options and allow more personalized treatment approaches.49

4. Future perspectives

The future of IBD treatment lies in precision medicine, with efforts directed toward identifying biomarkers that predict treatment response and disease progression. Advances in pharmacogenomics, transcriptomics, and microbiome research may enable more individualized treatment strategies, ensuring that patients receive the most appropriate therapy based on their specific disease characteristics.36

Additionally, the integration of artificial intelligence (AI) in clinical decision-making may allow for early identification of patients at risk of treatment failure, guiding personalized therapeutic choices. These advancements hold promise in further refining IBD management, minimizing adverse effects, and improving long-term outcomes.38

4.1. Limitations

Despite the growing body of evidence comparing biological therapies and traditional immunosuppressants, several limitations remain. Many clinical trials evaluating biologics have stringent inclusion criteria, which may not fully reflect real-world patient populations. Variability in patient response, influenced by genetic predisposition and gut microbiota composition, further complicates direct comparisons.

Additionally, long-term safety data for newer biologics are still emerging. While short-term results indicate favorable safety profiles, the risk of malignancy, opportunistic infections, and other long-term complications needs further evaluation. The economic impact of biologics, particularly in resource-limited settings, also warrants more extensive cost-effectiveness analyses.

5. Conclusion

The evolution of inflammatory bowel disease (IBD) treatment from traditional immunosuppressants to targeted biological therapies has significantly improved disease management, offering better long-term remission rates and reduced systemic side effects. While traditional agents such as thiopurines and methotrexate remain valuable due to their affordability and accessibility, biologics provide superior efficacy and safety, particularly in moderate to severe cases. However, challenges such as high costs, loss of response, and accessibility barriers persist. Future advancements in personalized medicine, biomarker-driven treatment selection, and novel therapeutic agents will further refine treatment strategies, ensuring better outcomes and improved quality of life for patients with IBD.