Effect of mequitazine on the pharmacokinetics of theophylline in asthmatic patients.

The effect of an oral anti-allergic drug, mequitazine, on the pharmacokinetics of theophylline has been investigated in seven asthmatic patients. They received chronic theophylline therapy (a sustained-release theophylline tablet 200-400 mg b.d. at 12 h intervals) and coadministered mequitazine 6 mg for 3 weeks. Plasma theophylline concentration-time curves and the urinary excretion of theophylline and its major metabolites before and after coadministration of mequitazine were compared. No significant change in the pharmacokinetic parameters of theophylline or in the urinary recovery of unchanged drug and its metabolites was observed. Thus, mequitazine did not influence the pharmacokinetics of theophylline and it should be safe for coadministration to asthmatic patients on chronic theophylline therapy.