Pharmacokinetics of mycophenolate mofetil following single-dose intravenous and single- and multiple-dose oral administration and clinicopathologic effects of mycophenolate mofetil following long-term oral administration in healthy horses

OBJECTIVE To characterize the pharmacokinetics of mycophenolate mofetil (MMF) following single-dose IV or PO administration, characterize the pharmacokinetics of MMF following long-term PO administration, and describe the clinicopathologic effects of long-term MMF administration in horses. ANIMALS 12 healthy adult horses. PROCEDURES In phase I, 6 horses received a single IV (2.5 mg/kg) or PO (5 mg/kg) dose of MMF in a randomized balanced crossover assessment (>= 2-week interval between administrations). In phase 2, 6 other horses received MMF for 60 days (5 mg/kg, PO, q 24 h for 30 days and then 5 mg/kg, PO, q 48 h for an additional 30 days). RESULTS Following IV (single-dose) or PO (single- or multiple-dose) administration, MMF was rapidly converted to mycophenolic acid. For single-dose PO administration, mean +/- SD maximum plasma mycophenolic acid concentration was 1,778.3 +/- 441.5 ng/mL at 0.71 +/- 0.29 hours. For single-dose IV administration, mean systemic clearance and volume of distribution at steady state were 0.689 +/- 0.194 L/h/kg and 1.57 +/- 0.626 L/kg, respectively. Following single doses, mean terminal half-life was 3.99 +/- 0.865 hours for IV administration and 4.02 +/- 1.01 hours for PO administration. The accumulation index following long-term PO administration was 1.0 +/- 0.002, and the terminal half-life was 4.59 +/- 1.25 hours following the final dose on day 60. None of the horses developed abnormal clinical signs or had any consistently abnormal clinicopathologic findings. CONCLUSIONS AND CLINICAL RELEVANCE Further investigation of the clinical efficacy of long-term MMF treatment of horses with autoimmune diseases is warranted.