... cimetidine decreases the renal clearance of dofetilide and of procainamide and its active metabolite NAPA. Chapter 005. Principles of Clinical Pharmacology (Part 11) Pharmacokinetic Interactions ... the risk of cyclosporine toxicity or of rhabdomyolysis with some HMG-CoA reductase inhibitors (lovastatin, simvastatin, atorvastatin), and P-glycoprotein inhibitors increasing risk of digoxin ... Phenytoin, an inducer of many systems, including CYP3A, inhibits CYP2C9. CYP2C9 metabolism of losartan to its active metabolite is inhibited by phenytoin, with potential loss of antihypertensive...