Influence of malnutrition on the disposition of metronidazole in rats

Metronidazole and antipyrine metabolism in the rat: clearance determination from one saliva sample

1. The applicability of a simple, non-invasive method for assessment of metronidazole and antipyrine metabolism in rats in vivo was investigated. 2. In 48 sample pairs of blood and pilocarpine-stimulated saliva from six rats the concentration of metronidazole was almost identical (r = 0.97). 3. In 26 rats the clearance could be determined from one sample without loss of precision and accuracy compared with conventional determinations (r = 0.99). If urine was collected for 24 h the fractional clearance representing each elimination pathway could be determined. 4. Pretreatment with phenobarbitone increased the fractional clearance of metronidazole by oxidation and glucuronidation 3.8-fold and 1.6-fold, respectively, whereas 3-methylcholanthrene pretreatment increased the rate of oxidation 10-fold and decreased the rate of glucuronidation 0.5-fold. 5. The clearance and fractional clearances of metronidazole and antipyrine administered in a mixture could be determined from the same saliva sample and urine collected for 24 h without drug-drug interactions. 6. Phenobarbitone pretreatment increased the formation rate of all metabolites of metronidazole and antipyrine administered in a mixture, whereas beta-naphthoflavone increased the formation rates of only the oxidative metronidazole metabolites, norantipyrine and 4-hydroxyantipyrine, but not metronidazole glucuronide or 3-hydroxymethylantipyrine. 7. A mixture of metronidazole and antipyrine and non-invasive sampling are recommendable for the study of the differential metabolism of foreign compounds in rats in vivo.

The effect of dietary energy and protein deficiency on drug metabolism

The influence of a diet deficient in energy or protein on hepatic oxidation (Phase I reactions) and glucuronidation (Phase II reactions) in man has been examined. Nine healthy volunteers were fed an energy deficient diet (daily energy intake 4.3 MJ; daily protein intake 0.94 g/kg) and a protein deficient diet (daily energy intake 11.4 MJ; daily protein intake 0.31 g/kg) in random order. The control energy and protein intakes were 12.0 MJ and 1.52 g/kg, respectively. Each test diet period lasted 12 days. On Day 10, antipyrine 1000 mg and metronidazole 500 mg were given and elimination in saliva was determined. The metabolism of neither drugs was changed during the two dietary interventions, nor was their clearance to metabolites. On Day 12, the metabolism of oxazepam 15 mg was studied. The energy deficient and the protein deficient diet reduced the clearance rate of oxazepam by 20.3%, and 14.1% respectively. The elimination half-life was prolonged by 17.4% after the former and by 11.4% after the latter diet. Thus, both a low energy and a low protein intake decreased the glucuronidation of oxazepam, whereas no effect was observed on the rate of oxidation, expressed as the metabolism of antipyrine and metronidazole.

The effects of age and dietary protein restriction on the pharmacokinetics of theophylline in the rat

The influence of dietary protein levels on theophylline kinetics was examined in male Fischer 344 virgin rats of 2, 14 and 20 months of age fed for four weeks on a 23% (control) or 5% (low) protein diet ad libitum. Protein deficiency led to a significant decrease in body weight gain for the 2 month old rats (10.9% versus 26.5%). In addition, decreases in total body weight of 7.5% and 15.3% were seen for the 14 and 20 month old rats, respectively, on a low protein diet. Total proteins and albumin levels in plasma were not significantly affected by age or dietary protein levels. After intravenous administration of 10 mg/kg aminophylline, the average mean residence time (MRT) was significantly longer in 20 month old rats as compared to the younger rats, while 14 month old rats had a greater elimination rate constant than the 2 and 20 month old rats. There were significant reductions in the mean steady-state apparent volume of distribution (Vss) in the 2 and 14 month old rats on a low protein diet of 31% and 18%, respectively, while there was no difference between the diets in 20 month old rats. In addition, the Vss decreased from 0.71 L/kg to 0.57 L/kg in the 2 and 20 month old rats, respectively, on a normal protein diet. Dietary protein deficiency led to a significant reduction of total body clearance from approximately 73 to 45 ml/hr/kg in the 2 and 14 month old rats.2+p

Metabolism of metronidazole and antipyrine in isolated rat hepatocytes. Influence of sex and enzyme induction and inhibition

The metabolism of metronidazole and antipyrine was investigated in freshly isolated hepatocytes from 7 male and 6 female control Wistar rats, 8 males and 5 females pretreated with phenobarbital (PB) and 3 males pretreated with 3-methylcholanthrene (MC). Pretreatment with PB increased the intrinsic clearance (CLi = Vmax/Km) of metronidazole to its acetic acid (MAA) and hydroxy metabolite (HM) 7- and 2.8-fold in the males and 3.2- and 3.0-fold in the females, whereas MC treatment increased the values 9- and 10-fold, respectively (P less than 0.05). The CLi of metronidazole to HM and its glucuronide conjugate was higher in the control and PB treated male than in the corresponding female groups, whereas the rank order was reversed for sulphate formation (P less than 0.05). SKF 525A was a more potent inhibitor of MAA formation than of HM formation, except in the PB treated male group. Pretreatment with MC increased the inhibitory potency of alpha-naphthoflavone and antipyrine toward MAA and HM formation. In male rats PB treatment increased the CLi of antipyrine to 3-hydroxymethyl-(HMAP), nor-(NORAP) and 4-hydroxyantipyrine (OHAP) 2.5-, 2.1- and 4.5-fold, respectively (P less than 0.05). Pretreatment with MC in male and with PB in female rats had no significant effect on antipyrine metabolism. SKF 525A was a more potent inhibitor of HMAP and OHAP formation than of NORAP formation. Treatment with MC increased the inhibitory potency of alpha-naphthoflavone toward the formation of all antipyrine metabolites. Metronidazole increased the formation rate of HMAP, but inhibited the formation of NORAP and OHAP, particularly the latter. The results suggest that the formation of MAA, HM, HMAP, NORAP and OHAP from metronidazole and antipyrine is catalyzed by different cytochrome P-450 isozymes, which may be supplemented or substituted by PB or MC induced species. The involved P-450 isozymes have more or less overlapping substrate and product specificity. Metronidazole appears to be a sensitive probe for detection and identification of PB and MC type induction.