Concurrent monitoring of central carbamazepine and transmitter amine metabolism and motor activity in individual unrestrained rats using repetitive withdrawal of cerebrospinal fluid.

A method for repeated withdrawal of cerebrospinal fluid (CSF) from the cisterna magna was used in a pharmacokinetic and behavioural study of conscious, freely-moving rats, given the antiepileptic drug carbamazepine (35 mg/kg i.p.). Pharmacokinetic constants (i.e. time to peak concentration, peak concentration, area under the curve and t 1/2) for the drug and its primary metabolite carbamazepine-10,11-epoxide and also concentrations of acidic metabolites of 5-hydroxytryptamine and dopamine were obtained for the CSF of individual rats. A pharmacodynamic constant, the effective concentration of drug in CSF for 50% inhibition of motor activity was also determined for each animal. The above data provides good indices of the corresponding values for carbamazepine and its metabolite in brain insofar as a separate experiment showed good correlations between CSF and brain for concentrations of both the drug and its metabolite. Carbamazepine appeared to be largely responsible for the depression of motor activity as the metabolite, at the levels attained, seemed to have little effect. The changes in motor activity were not associated with altered concentrations of the metabolites of 5-hydroxytryptamine or dopamine in the CSF. While the investigation did not reveal major advantages in monitoring the drug under study in CSF rather than in serum it illustrates the potential of the CSF method as a simple way to obtain neuropharmacokinetic and neuropharmacodynamic profiles of the action of drugs in individual rats.