Procainamide tubular secretion

The answer is c. (Hardman7 p 906. Katzung, p 1127) Cimetidine inhibits proximal tubular secretion of procainamide, resulting in increased plasma concentrations of procainamide and its active metabolite, N-acetylprocainamide. 

Drugs that may be affected by trospium include those eliminated by active tubular secretion (eg, digoxin, procainamide, pancuronium, morphine, vancomycin, metformin, and tenofovir). 

H2 antagonists compete with creatinine and certain drugs (eg, procainamide) for renal tubular secretion. All of these agents except famotidine inhibit gastric first-pass metabolism of ethanol, especially in women. Although the importance of this is debated, increased bioavailability of ethanol could lead to increased blood ethanol levels. 

Trimethoprim inhibits the active tubular secretion of procainamide (198). 

Somogyi A, McLean A, Fleinzow B. Cimetidine-procainamide pharmacokinetic interaction in man evidence of competition for tubular secretion of basic drugs. Eur J Clin Pharmacol 1983 25 339-345. 

A a Eh X 0 a e Eh P) t=L Use with caution in patients over 50 years oid with kidney or liver faiiure. PO/IV/IM. Little plasma protein binding, little metabolism. Cimetidine increases serum concentrations of many drugs (oral anticoagulants, theophylline, lidocaine, phenytoin, benzodiazepines, nifedipine, propranolol) by inhibiting liver P450 enzymes. May inhibit renal tubular secretion of procainamide. ... 

Trimethoprim decreases the renal clearance of both procainamide and its active metabolite by competing for active tubular secretion. It may also cause a small increase in the conversion of procainamide to A-acetylpro-cainamide. ... 

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