Inhibition of clearance of dyphylline by probenecid

Dyphylline versus theophylline: a double-blind comparative evaluation

This study was a randomized double-blind evaluation of three doses of dyphylline, theophylline, and placebo for blocking exercise-induced bronchospasm (EIB). Twenty patients aged 12 to 17 years took one of the following on five separate days prior to an exercise challenge: 10, 15, or 20 mg/kg dyphylline; 6 mg/kg anhydrous theophylline; or placebo. Linear relationships were found between the log of dyphylline doses and per cent changes from baseline for PEFR, FEV1 and FEF25-75%. The 15 and 20 mg/kg doses differed significantly from placebo in preventing declines in PEFR, FEV1, and FEF25-75%. While significant, these changes were one half to one third those found with 6 mg/kg theophylline. Tremor was twice as common with theophylline. While dyphylline has therapeutic effectiveness compared to placebo for blocking EIB, its benefit is small. Further evaluations are needed to elucidate optimal dosaging for maximal effectiveness.

Effect of probenecid on the pharmacokinetics of aminophylline

The authors investigated the effect of probenecid on the pharmacokinetics of aminophylline. Seven normal volunteers served as their own controls in a crossover study. In the first phase, subjects received an oral dose of aminophylline after an overnight fast. In the second phase, probenecid was given orally 30 minutes prior to the administration of aminophylline. Serum and urine theophylline levels were determined by high performance liquid chromatography. Statistical analysis showed that probenecid had no significant effect on any of the pharmacokinetic parameters measured. Probenecid appears to have little or no influence on the liver metabolism of theophylline.