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[Bioavailability of penicillin V in aqueous dosage forms].

The bioavailability of Megacillin-oral-Trockensaft (active substance: potassium salt of phenoxymethylpenicillin, penicillin V potassium) was compared with that of another commercially available drug containing the same active substance. In a cross-over study, 12 healthy volunteers were administered by oral route 10 ml of each preparation (equivalent to 600 000 U = 392.2 mg potassium salt of phenoxymethylpenicillin) under standardized experimental procedure. Relative bioavailability was assessed by determination of phenoxymethylpenicillin concentrations in the plasma, employing both microbiological assay as well as high-performance liquid chromatography, by computation of the areas under the plasma concentration curves, and by calculation of the time periods necessary for the attainment of maximum plasma concentrations. In order to assess differences between the two forms in duration of efficacy, calculation of time intervals were based on plasma concentrations which were above 0.5; 1.0 or 1.5 micrograms/ml, respectively. Results of this comparative study indicate that Megacillin-oral-Trockensaft is superior to the other commercial preparation. The considerably better bioavailability of Megacillin-oral-Trockensaft is attributed to a substantially higher absorption rate and to a 2.4 times greater extent of absorption. Due to the distinct advantage in the bioavailability of Megacillin-oral-Trockensaft peak plasma concentrations of phenoxymethylpenicillin 5-6 fold higher and are reached faster when compared with those following intake of the other form tested. In practice, the superior bioavailability of Megacillin-oral-Trockensaft guarantees quicker initiation of therapeutic activity and greater safety (higher plasma concentrations, prolonged effect).

Adult↗

Pharmacokinetics of papaverine hydrochloride and the biopharmaceutics of its oral dosage forms.

The pharmacokinetics of completely metabolized papaverine hydrochloride were characterized by a linear sum of three exponentials on intravenous administration with respective 1.5, 19 and 107 min apparent half lives. There was a time-dependent partition from plasma water into red blood cells with an apparent half life of 1.5--3 min. The partition coefficient normally ranged between 8 and 15 at therapeutic levels but approached unity at high plasma concentrations to indicate a saturable partition. Apparent compartmental volumes of distribution referenced to total concentrations in the plasma were 4.3--4.8, 11--13 and 20--25 liters. Protein binding was 91--95%. The hepatic clearance of blood was 960 ml/min, corresponding to a hepatic efficiency of 69%, and indicated that the clearance of protein-bound drug was consistent with the observed first pass metabolism of 70% for oral solutions. No dose dependency was observed on intravenous administration or on oral administration of solutions and tablets. Tablets with release lag times of 10--15 min showed relative bioavailabilities of 52%. Two different lots of sustained release capsules showed 68 and 89% relative bioavailabilities. Release lag times among capsules ranged between 0 and 170 min. Loo-Riegelman calculations and analog computer fittings were consistent with a half life of absorption from oral solutions of 19 min and zero order release rates from tablets and sustained release capsules. Chronic studies of tablets q.i.d. and capsules b.i.d. confirmed lack of accumulation. An appropriately designed 300 mg sustained release capsule, b.i.d., for an arbitrary plasma level of 0.200 microgram/ml should have one tenth the release rate of the studied capsules.

Administration, Oral↗

Proton magnetic spectroscopic (PMR) determination of diphenhydramine hydrochloride in dosage forms.

Direct dissolution of the bulk material, capsule, or freeze-dried solution for injection and an internal standard in chloroform-d and recording of the PMR spectra provides a simple, specific, and accurate assay method form diphenhydramine hydrochloride [2-(diphenyl-methoxy)-N,N-dimethylethanamine hydrochloride] in pharmaceutical samples. The drug content can be calculated from the integral values for the N-methyl protons of diphenhydramine at ca. 2.85 ppm and for the methyl protons of tert-butyl alcohol at ca. 1.27 ppm. The mean +/- SD% recoveries from synthetic mixtures simulating capsules and injectables were 100.0 +/- 0.2 (n = 11) and 100.1 +/- 0.4 (n = 4), respectively. The method also permits the detection of degradation of diphenhydramine such as benzhydrol, diphenylchloromethane, and 2-(dimethylamino)ethanol to a minimum of about 2% of the parent compound.

Administration, Oral↗