Generalized penicillin epilepsy in the cat and the brain uptake of carbamazepine

Distribution of diphenylhydantoin in the brain during experimental status epilepticus of the cat

The distribution of diphenylhydantoin (PHT) (40 mg/kg i.p.) in the brain was investigated in cats with convulsive generalized (group 1) and focal penicillin-induced status epilepticus (group 2), and in controls. A significant increase in the amount of PHT entering the brain during the convulsive status was found, with peak brain levels at 45 min (12 +/- 3.2 micrograms/g vs. 6.0 +/- 0.8 in normal cats, P less than 0.05). In the focal status brain concentrations of PHT reached levels intermediate between controls and group 1 cats. At 15 min, elevated blood levels of the drug were paralleled by increased concentrations in the brain, whereas at 30 and 45 min other factors, such as changes in cerebral blood flow, cerebral pH, vascular resistance, metabolic derangement and blood-brain barrier disruption were presumably responsible for the altered brain PHT uptake. The relevance of these data to clinical practice is discussed, in relation to the treatment of human status epilepticus and the potentially neurotoxic effects of the drug.

Brain distribution of carbamazepine and phenobarbital given in combination in experimental epilepsy

This study describes the brain distribution of carbamazepine (CBZ) and phenobarbital (PB) given intraperitoneally in combination to cats rendered epileptic by parenteral penicillin and by penicillin topically applied on neocortex. A control group of normal cats was also evaluated pharmacokinetically. Levels of both drugs were extremely low in brains of controls (CBZ 0.8 +/- 0.02 micrograms/g; PB 1.49 +/- 0.7 micrograms/g of fresh tissue), but higher levels were found in brains of epileptic cats with CBZ showing the greater increase (peak concentrations five- to sixfold higher than the corresponding CSF free fraction vs. three- to fourfold higher for PB). This might have been partially due to the ability of CBZ to prevent the metabolic alterations associated with severe convulsions, and hence the binding impairment. As this event had no effect of potentiation on CBZ anticonvulsant activity, the present data confirm previous reports indicating that there is no experimental evidence that two drugs are better than one in controlling epilepsy.

The penetration of phenobarbital in generalized and focal penicillin-induced epileptic brain of the cat

The penetration of phenobarbital (PB) into cerebral tissue was determined in cats rendered epileptic by parenteral penicillin and in cats with focal penicillin-induced epilepsy. The results were compared with those from normal controls. In both kinds of experimental models of epilepsy, PB penetration was impaired, although a gradual and progressive accumulation of the drug in the brain tissue was observed in all three groups of cats (binding occurring from time 30 min on). Similar to the events with other substances, such as carbamazepine, the prolonged epileptic activity may have contributed to the impaired penetration of PB, because of severe metabolic alterations secondary to seizures. The present data confirm previous reports indicating that epileptic seizures alter the pharmacokinetics of drugs.

Normal brain distribution of carbamazepine in cat penicillin focal epilepsy

Carbamazepine (CBZ) brain distribution was studied in cats rendered epileptic by penicillin topically applied on neocortex. CBZ penetration into the focus did not differ significantly from penetration into the other areas of the brain, with the drug rapidly entering the cerebral tissue (peak at 30 min). As no difference was found between CBZ brain concentrations at 15 and 90 min, substantial early binding of the drug was confirmed in this experimental model of epilepsy. As CBZ was able to decrease rapidly the spike frequency of the penicillin focus, it may be speculated that it was also able to prevent the metabolic alterations associated with severe epileptogenesis that would have caused an impaired CBZ brain distribution.