Azathioprine Dosing for Retinal Vasculitis
For patients with retinal vasculitis, azathioprine should be dosed at 1.5-2 mg/kg/day, with dose adjustments based on age and renal function, and maintained for 18 months to 4 years after achieving remission. 1
Initial Dosing and Adjustments
Azathioprine dosing should follow this algorithm:
- Standard dosing: 1.5-2 mg/kg/day 1
- Age-based adjustments:
- Age >60 years: Reduce to 1.5 mg/kg/day
- Age >70 years: Reduce to 1.0 mg/kg/day 1
- Renal function adjustment:
- GFR <30 ml/min/1.73 m²: Reduce by 0.5 mg/kg/day 1
Duration and Tapering Schedule
The optimal maintenance therapy duration with azathioprine should follow this schedule:
- Initial phase: 1.5-2 mg/kg/day for 18-24 months after achieving complete remission 1
- Intermediate phase: Decrease to 1 mg/kg/day until 4 years after diagnosis 1
- Tapering phase: Reduce by 25 mg every 3 months until discontinuation 1
Combination Therapy
Azathioprine should be combined with glucocorticoids:
- Glucocorticoids should be continued at 5-7.5 mg/day for 2 years 1
- After 2 years, slowly reduce by 1 mg every 2 months 1
Efficacy in Retinal Vasculitis
Azathioprine has demonstrated effectiveness in retinal vasculitis, particularly in:
- Reducing relapse rates 2
- Maintaining or improving visual acuity in 64% of patients 2
- Decreasing ocular inflammatory scores in 56% of cases 2
For patients with Behçet's disease-associated retinal vasculitis, azathioprine at 2.5 mg/kg/day has shown complete response in 51.6% of patients and partial response in 41.4% 3. However, patients with retinal vasculitis at diagnosis are less likely to achieve complete remission (odds ratio 0.45) 3.
Alternative Maintenance Options
If azathioprine is not tolerated, consider these alternatives:
- Mycophenolate mofetil (MMF): 2000 mg/day in divided doses 1
- Methotrexate: Initially 0.3 mg/kg/week (maximum 25 mg/week), but avoid if GFR <60 ml/min/1.73 m² 1
Monitoring and Safety Considerations
- Regular complete blood counts and liver function tests should be performed
- Monitor for signs of myelosuppression, hepatotoxicity, and infection
- Approximately 8-24% of patients may experience side effects requiring discontinuation 2, 3
- Provide Pneumocystis jirovecii pneumonia prophylaxis with trimethoprim/sulfamethoxazole 4
Special Considerations for Severe Disease
For severe retinal vasculitis:
- Consider initial induction therapy with cyclophosphamide or rituximab before transitioning to azathioprine maintenance 1, 5
- For Behçet's disease with retinal vasculitis, a combination of pulse cyclophosphamide and azathioprine may be more effective than azathioprine alone 5
The evidence strongly supports azathioprine as an effective maintenance therapy for retinal vasculitis, with appropriate dose adjustments based on patient factors and careful monitoring for adverse effects.