comparative bioavailability of theophylline whole and halved sustainedrelease tablets in a randomised multipledose crossover study in 14 healthy volunteers plasma theophylline concentrations were compared during a 12hour dosing interval after repeated administration of theophylline euphyllin retard byk gulden as whole and halved tablets bioavailability of theophylline from the halved tablets relative to the whole tablets was 116 100 134 for the extent of absorption as judged by the area under the concentration time curve auc and 115 99 135 for the rate of absorption as judged by maximum concentration cmax the confidence levels for the 80120 bioequivalence range were 72 auc and 76 cmax those for the 80 and 125 range were 91 auc and 91 cmax the plateau times t75 cmax which characterise the sustainedreleased properties were 85 29 hours halved and 83 25 hours whole during the 12hour dosing interval it is concluded that no clinically relevant deviations in steadystate plasma theophylline concentration and sustainedrelease properties are likely to result from breaking halving the filmcoated tablets