Pacifici GM, Cuoci L, Placidi GF. Disposition, distribution, plasma protein binding and biliary excretion of pinazepam after i.p. administration to rat.
Eur J Drug Metab Pharmacokinet 1983;
8:209-17. [PMID:
6418547 DOI:
10.1007/bf03188750]
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Abstract
The pharmacokinetics, distribution, plasma protein binding and the biliary excretion of pinazepam were studied in the rat. The drug was administered (5 mg/kg) by i.p. injection. The chemical analysis of pinazepam and its metabolites was carried out by a gas-chromatographic method. The parent compound was rapidly absorbed, accumulated into the tissues and converted into N-desmethyldiazepam. The highest plasma levels of the parent compound (367 +/- 13 ng/ml) were found 3 min after administration. The volume of distribution and the clearance of the drug were 1315 ml and 7.23 ml/min respectively. The metabolite was detected in the plasma and tissues 3 min after administration. At this sampling time its concentrations were 76 +/- 16 ng/ml in the plasma and 1081 +/- 68 ng/g in the liver. The decay curve of both pinazepam and N-desmethyldiazepam in the plasma, liver, lung, heart, kidney, brain, and gastrochemius muscle were characterized for their Kel, t 1/2, and AUC values. The tissue AUC to plasma AUC ratios indicated a preferential accumulation of pinazepam over its metabolite in the tissues. The plasma protein binding of pinazepam was measured by dialysis at the equilibrium. Rat plasma proteins bound 89.17 +/- 0.20 percent of the drug. The association constant was 2.60 X 10(3) l/mole and the number of sites 0.44 X 10(-6) sites/g. The biliary excretion of pinazepam and N-desmethyldiazepam was poor.
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