Pathophysiology And Rationale
- Chronic inflammation results from imbalance between proinflammatory and anti-inflammatory cytokines.
- Proinflammatory cytokines driving disease include tumor necrosis factor-alpha, interleukin-1, interleukin-6, interleukin-8, interleukin-12, and interferon-gamma.
- Biologics act as targeted therapies modulating specific immune system components to decrease inflammatory responses.
- Precise targeting prevents damage to innocent bystander cells, unlike conventional systemic immunosuppression.
Indications For Biologic Therapy
- Indicated for refractory polyarthritis failing conventional synthetic disease-modifying antirheumatic drugs.
- Severe systemic juvenile idiopathic arthritis (sJIA) with or without macrophage activation syndrome.
- Refractory enthesitis-related arthritis and sacroiliitis.
- Severe, chronic anterior uveitis refractory to topical or conventional systemic therapy.
Pre-Treatment Evaluation And Screening
- Exclude active and latent tuberculosis prior to initiation.
- Screening requires chest radiograph, Mantoux test, and interferon-gamma release assay.
- Mandates screening for infectious hepatitis B, hepatitis C, and human immunodeficiency virus.
- Live attenuated vaccines remain strictly contraindicated during biologic therapy.
- Update killed vaccines like pneumococcal, Haemophilus influenzae type B, and annual inactivated influenza before initiation.
Classification And Pharmacotherapy
Table 1: Biologic Agents In Juvenile Idiopathic Arthritis
| Drug Class | Agent | Mechanism Of Action | Administration & Dosage | Specific Indications |
|---|---|---|---|---|
| Tumor Necrosis Factor Antagonists | Etanercept | Soluble tumor necrosis factor receptor p75 fusion protein binding soluble tumor necrosis factor-alpha. | Subcutaneous. 0.8 mg/kg weekly. | Polyarticular disease, extended oligoarthritis. Avoid in uveitis. |
| Tumor Necrosis Factor Antagonists | Adalimumab | Humanized IgG1 monoclonal antibody binding tumor necrosis factor-alpha. | Subcutaneous. 10-40 mg every other week based on weight. | Polyarticular disease, enthesitis-related arthritis, refractory uveitis. |
| Tumor Necrosis Factor Antagonists | Infliximab | Chimeric human/mouse monoclonal antibody neutralizing tumor necrosis factor-alpha. | Intravenous. 5-10 mg/kg every 4-8 weeks. | Polyarticular disease, severe uveitis. |
| Interleukin-1 Antagonists | Anakinra | Recombinant human interleukin-1 receptor antagonist. | Subcutaneous. 1-2 mg/kg daily. | Systemic juvenile idiopathic arthritis, macrophage activation syndrome. |
| Interleukin-1 Antagonists | Canakinumab | Monoclonal antibody to interleukin-1 beta. | Subcutaneous. 2-4 mg/kg every 4 weeks. | Systemic juvenile idiopathic arthritis. |
| Interleukin-6 Antagonists | Tocilizumab | Humanized anti-human interleukin-6 receptor monoclonal antibody. | Intravenous or subcutaneous. Dose varies by weight (<30kg vs >30kg). | Systemic juvenile idiopathic arthritis, polyarticular disease. |
| T-Cell Costimulation Modulators | Abatacept | Soluble fusion protein of CTLA-4 linked to Fc portion of IgG1. Inhibits CD80/CD86. | Intravenous or subcutaneous. Intravenous given every 4 weeks. | Polyarticular disease refractory to tumor necrosis factor inhibitors. |
| B-Cell Depleting Agents | Rituximab | Chimeric monoclonal antibody targeting CD20 on B-lymphocytes. | Intravenous. 750 mg/m2 or 375 mg/m2. | Refractory polyarthritis, Epstein-Barr virus triggered macrophage activation syndrome. |
| Janus Kinase Inhibitors | Tofacitinib | Small molecule inhibiting Janus kinase 1 and Janus kinase 3. | Oral. Dose varies by weight (3.2 mg to 5 mg twice daily). | Polyarticular disease. |
Adverse Effects And Clinical Monitoring
- Increased susceptibility to serious bacterial, mycobacterial, and opportunistic infections.
- Reactivation of latent tuberculosis and hepatitis B virus.
- Increased risk for demyelinating disorders and lupus-like syndrome seen with tumor necrosis factor antagonists.
- Immunogenicity leading to human anti-chimeric antibodies and human anti-human antibodies, causing secondary loss of efficacy.
- Tocilizumab therapy requires monitoring for elevated liver transaminases, hyperlipidemia, and cytopenias.
- Routine evaluation includes complete blood count and liver function tests every three months during ongoing therapy.
- Biologics targeting interleukin-1 and interleukin-6 control systemic inflammation but do not completely prevent macrophage activation syndrome occurrences.