1 Plasma theophylline concentrations following administration of sustained-release (SR) theophylline tablets were determined in ten healthy volunteers using a dose of 190 mg or 380 mg 12 hourly. 2 The plasma theophylline levels during the first 12 h period confirmed the sustained-release formulation characteristics, with the plasma drug concentrations reaching a plateau for the last 6 hours. 3 During the fifth 12 h dosing period the mean maximum and minimum plasma theophylline concentrations were 7.25 and 4.30 microgram/ml after 190 mg SR theophylline 12 hourly (n = 6) and 12.96 and 7.36 microgram/ml after 380 mg 12 hourly (n = 5), although there was marked between-subject variation in plasma theophylline concentrations. 4 One subject withdrew from the study due to side effects, which were more common when the higher dose of SR theophylline was given.
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