Relative Bioavailability Studies on Paracetamol in Suppositories as Compared to Tablets. Relative bioavailabilities of 250 mg paracetamol (CAS 103-90-2) in ben-u-ron 125 mg and ben-u-ron 250 mg suppositories were determined in comparison with that of cut-in-half Benuron tablets 500 mg in an open intraindividual 3-period-changeover-study in 18 healthy volunteers. Plasma concentrations of paracetamol were analyzed by means of a specific and sensitive HPLC-method with UV-detection. For the assessment of the bioavailability AUC, Cmax, tmax and HVD (half value duration) were used as pharmacokinetic characteristics. Relative bioavailability of paracetamol was 102% for 125 mg and 93% for 250 mg suppositories, compared with that of cut-in-half 500 mg tablets. Mean maximum paracetamol plasma concentrations (Cmax) were determined as 2.1 micrograms/ml (CV = 31%; (CV = Coefficient of Variation), 2.0 micrograms/ml (CV = 27%) and 3.5 micrograms/ml (CV = 27%) after administration of 125 mg and 250 mg suppositories and 500 mg cut-in-half tablets, respectively. These maximum concentrations were achieved 2.2 +/- 0.7, 1.8 +/- 0.7 and 0.6 +/- 0.3 h (tmax) after administration of the respective preparations. The corresponding HVD-values were 3.8 +/- 1.0, 3.5 +/- 0.9 and 1.8 +/- 0.8 h, respectively. Extent of bioavailability of paracetamol (dose: 250 mg) following administration of 125 mg as well as 250 mg suppositories in comparison with 500 mg tablets was shown to be equivalent. The results obtained in this study confirm the adequate bioavailability of both suppositories compared with tablets. On the other hand both suppository preparations were assessed as being bioequivalent concerning AUC and Cmax.