Theophylline concentrations in serum and saliva after oral microcrystalline and sustained-release preparations in asthmatics.

Theophylline concentrations in saliva have been compared with those in serum in 13 asthmatic patients after single and multiple oral dosage of a microcrystalline theophylline tablet (Nuelin) and a sustained-release preparation (Nuelin Retard). There was wide individual variation in the ratio of serum to saliva concentrations indicating that, even when individual serum to saliva ratios have been established, the use of saliva theophylline measurements alone is unreliable for the routine monitoring of theophylline therapy. Both preparations produced mean serum theophylline concentrations within the 10--20 mcg/ml range, the sustained-release tablet giving higher monitoring through values and smaller through to peak variation. The preparations were equally and highly bioavailable. Side effects were reported by three patients, which were the patients with the highest AUC. The Nuelin Retard preparation appears to provide smooth, sustained serum theophylline concentrations within the therapeutic range and the simple, twice-daily dosage should result in improved patient compliance.