EFFECTS OF CIMETIDINE AND RANITIDINE ON THE PHARMACOKINETICS OF A CHRONOTHERAPEUTICALLY FORMULATED ONCE-DAILY THEOPHYLLINE PREPARATION (UNIPHYL(R))

The effects of cimetidine and ranitidine on the steady-state pharmacokinetics, safety, and efficacy of a chronotherapeutically formulated (CTF), once-daily theophylline preparation (Uniphyl(R)) were evaluated in 12 adult patients with asthma. In this randomized, double-blind, three-way crossover study, patients received a fixed dose of CTF-theophylline and concurrent cimetidine, ranitidine, or placebo for a period of 7 days each. Asthma symptoms, drug side effects, and beta2-agonist inhaler use were recorded daily. Venous blood sampling for pharmacokinetic assessment was done over a complete dosing interval on day 7 of each phase. Coadministration of cimetidine, but not ranitidine, was associated with a significant decrease in the apparent oral clearance of theophylline (2.47 +/- 0.91 vs 1.85 +/- 0.63 L/hr; P=0.004) and increases in the theophylline area under the curve (233.48 +/- 58.99 vs 307.43 +/- 79.07 mg/L/hr; P=0.003), peak concentration (13.2 +/- 2.8 vs 16.7 +/- 3.7 mg/L; P= 0.002), and trough concentration (6.4 +/- 2.5 vs 9.0 +/- 3.0 mg/L; P=0.008). Despite the changes in theophylline pharmacokinetic parameters during cimetidine treatment, no significant differences in asthma symptom scores or side effects were seen when once-daily CTF-theophylline was administered concomitantly with cimetidine, ranitidine, or placebo.