Pharmacokinetic interaction between theophylline and erythromycin.

Abstract

1 The pharmacokinetics of a single intravenous dose of theophylline alone and during the fifth day of treatment with 500 mg erythromycin every 8 h was studied in six healthy subjects. 2 At the same time the pharmacokinetics of erythromycin at steady‐state on the fourth day of the treatment (alone) and the fifth day (during the theophylline co‐ administration) were also studied. 3 Mean +/‐ s.d. theophylline clearance was decreased from 62 +/‐ 15.4 to 53 +/‐ 10.3 ml min‐1 (P less than 0.05) and elimination half‐life rose from 7.1 +/‐ 1.9 to 7.7 +/‐ 2 h (P less than 0.05) when erythromycin was co‐administered. 4 Mean +/‐ s.d. erythromycin area under the curves (0‐8 h) and (0‐oc) were reduced from 6.09 +/‐ 3.2 to 3.8 +/‐ 2.5 micrograms ml‐1 h and 7.2 +/‐ 3.6 to 5.0 +/‐ 2.9 micrograms ml‐1 h (P less than 0.05) in the presence of theophylline. Mean steady state and maximum steady state concentrations were also reduced from 0.75 +/‐ 0.4 to 0.47 +/‐ 0.3 microgram ml‐1 (P less than 0.05) and 1.45 +/‐ 0.87 to 0.85 +/‐ 0.51 microgram ml‐1 (P less than 0.05) respectively. 5 The potential clinical implications of this indication should be considered. 1982 The British Pharmacological Society