Unchanged Protein Binding and the Increase of Serum Diazepam Levels after Food Intake

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Abstract
Seven subjects received diazepam 0.3 mg/kg i.v. twice with a 2 wk interval between the doses. The subjects ingested a fatty or carbohydrate meal in a cross-over fashion 4 h after the injection on both experimental days. Venous blood samples were drawn 2, 3, 4, 5 and 6 h after the injection of diazepam for measurement of the serum levels of total and free (unbound) diazepam, N-desmethyldiazepam and free fatty acids. Serum levels of diazepam decreased progressively with time until the food intake, after which a significant (P < 0.01) postprandial increase (average 23%) occurred with both diets as compared to the preprandial levels at 4 h (average 240 ng/ml). Serum levels of free fatty acids decreased significantly both after a fatty (P < 0.01) and a carbohydrate (P < 0.05) meal. Diazepam was extensively (96-98%) bound to proteins and no changes in its protein binding was found. The late impairment of psychomotor skills that occurred with an increase in the diazepam serum level after its i.v. administration was probably due to its re-mobilization from a storage site rather than to variations in its protein binding.