Effect of tetracycline hydrochloride on theophylline kinetics

The effect of tetracycline hydrochloride on theophylline kinetics was studied. Eight nonsmoking men received a 15-minute infusion of theophylline (aminophylline) 5 mg/kg before (control) and after (experimental) a seven-day tetracycline course of 1 g daily. Each subject acted as his own control. Multiple serum samples were collected for 24 hours after each dose and were analyzed for theophylline by enzyme immunoassay. At each phase of study the mean +/- S.D. pharmacokinetic values were as follows: apparent volume of distribution (liter/kg), 0.44 +/- 0.05 (control) and 0.42 +/- 0.04 (experimental); clearance (ml . min/kg) 0.82 +/- 0.15 (control) and 0.73 +/- 0.07, (experimental); and elimination half-life (hours), 6.27 +/- 1.08 (control) and 6.72 +/- 0.78 (experimental). Tetracycline did not significantly alter the kinetics of theophylline. The probability of missing a 25% change in the kinetic values (Type II error) was less than 6%. Patients receiving theophylline do not appear to be at added risk for the development of toxicity as a result of a kinetic interaction when tetracycline hydrochloride is added to the therapeutic regimen.