Use

Leflunomide is a disease-modifying antirheumatic drug approved for therapy of rheumatoid arthritis and is used off-label to reduce viral nephritis in kidney transplant. It is a prodrug that converts to its active metabolite, teriflunomide, which inhibits pyrimidine synthesis. Due to variability in leflunomide pharmacokinetics, therapeutic monitoring of serum teriflunomide concentrations can aid in optimizing therapy. Serum concentrations greater than 40 mcg/mL have been correlated with better outcomes, especially in managing adverse reactions like diarrhea, hypertension, and liver toxicity. Assessment may be necessary for patients planning pregnancy due to potential teratogenic risks associated with the drug.