Use of cyclophosphamide in rheumatic diseases
- • Available formulations: 25-and 50-mg tablets; 100-, 200-, 500-, and 1000-mg vials.
- • Dosage: multiple dosing regimens including (1) daily oral, 50 to 200 mg (0.7–2 mg/kg per day); (2) monthly IV, 0.5 to 1 g/m 2 body surface area or 15 mg/kg; and (3) 500 mg IV every 2 weeks for 6 doses (Euro-Lupus).
Pearl: dose of cyclophosphamide is based on actual body weight even if patient is obese.
- • Cost (150 mg/day): oral generic tablets $1100/month.
- • Follow-up: daily dosing, CBC every 2 weeks until stable dose, then monthly; serum creatinine, blood urea nitrogen, and electrolytes every 2 to 4 weeks, liver transaminases every 4 weeks. Urinalysis monthly while on therapy; urinalysis with cytology every 12 months after cessation of therapy. For monthly dosing, CBC, urinalysis, and pregnancy test (women) before each dose, CBC 10 to 14 days after each dose to see nadir. If total white blood cell (WBC) count falls below 3500/mm 3 or neutrophil count falls below 1500/mm 3 at the nadir, the dose should be reduced by 20% to 25%. If the nadir total WBC count is above 4000/ mm 3 , the dose may be increased if patient’s disease is not controlled.
- • Precautions: avoid in pregnancy, avoid live vaccines, use lower doses in elderly due to less bone marrow reserve (cellularity = 100%–age). Cimetidine and allopurinol increase frequency of leukopenia. IV cyclophosphamide interferes with stable Coumadin dosing.