Lack of effect of magnesium-aluminium hydroxide on the absorption of theophylline given as a pH-dependent sustained release preparation.

Antacids can modify the pharmacokinetic parameters of sustained-release preparations of theophylline by changing the gastric pH. Though this has been studied with various theophylline/antacid combinations, the specific preparations investigated here have not previously been tested. The objective of the study was to assess any change in the availability of theophylline from a sustained-release preparation (SR), induced by the coadministration with an antacid. The study was designed as a double-blind randomized crossover trial in the Pneumology Departments of three general hospitals. Fifteen patients were studied. They all had stable asthma treated with theophylline and no major organ failure or gastro-intestinal lesions requiring the use of antacids. The antacid (aluminium hydroxide 800 mg and magnesium hydroxide 800 mg), or placebo, tid, was added to a stable regimen of theophylline SR bid, for 4 days, in crossover fashion. Plasma theophylline concentrations were measured before and 1, 2, 3, 4, 6, 8, 10, 12, 16 and 24 h after the morning dose of Armophylline on the fourth day of each treatment period; the maximum plasma concentration (Cmax), and time to Cmax (tmax) were noted, and the area under the 24-h time-concentration curve (AUC0-24) and mean plasma concentration (Cmean) were computed. Peak expiratory flows on the same day, before and 3, 6 and 12 h after the morning dose of Armophylline were also measured. There was no change in any of the parameters studied. The addition of the antacid to theophylline, each given according to standard clinical practice, did not modify the pharmacokinetics of the latter.(ABSTRACT TRUNCATED AT 250 WORDS)