In vivo microdialysis to determine the relative pharmacokinetics of drugs.
ABSTRACT The purpose of this study was to evaluate a simultaneous microdialysis method in blood and brain striatum to determine the relative pharmacokinetics and metabolism of L-3,4-dihydroxypenylalanine (L-dopa). L-Dopa (250 mumol/kg) was administered to rats with or without the aromatic amino acid decarboxylase (AADC) inhibitor carbidopa (25 mumol/kg) or benserazide (25 or 62.5 mumol/kg). L-Dopa, its metabolites, and AADC inhibitors in dialysates were analyzed by high performance liquid chromatography with an electrochemical detector. A moment analysis was also made to obtain pharmacokinetic parameters. After administration of L-dopa alone, it and its related metabolites were detected in both dialysates of blood and brain striatum. Coadministration of carbidopa (25 mumol/kg) or benserazide (62.5 mumol/kg) significantly enhanced the striatal amount of L-dopa by 8.0 and 6.1 times, respectively. Carbidopa and benserazide also increased striatal amounts of L-dopa metabolites, such as 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 3-methoxy-4-hydroxyphenylethyleneglycol. Inhibition effect of benserazide on an extracerebral decarboxylation of L-dopa to dopamine (DA) was stronger than that of carbidopa. Carbidopa showed a higher striatal level of DA than benserazide. These results suggest a different effect of the two inhibitors on the DA formations in blood and brain striatum, and on the L-dopa transport through the blood-brain barrier (BBB). Thus, microdialysis is an easy and available method for simultaneously assessing the in vivo relative pharmacokinetics and metabolism of drugs in systemic circulation and a target organ.
- SourceAvailable from: Craig E LunteJournal of Pharmaceutical Sciences 06/2000; 88(1):14 - 27. · 3.13 Impact Factor
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ABSTRACT: Simultaneous brain microdialysis in tumour and non-tumour tissues has been used for kinetic determination of the local distribution of an anticancer agent, cisplatin, in rats. Rat brain was implanted with 9L malignant glioma and cisplatin (3.5 mg kg-1) was administered as a selective intracarotid infusion for 30 min to rats prepared for brain microdialysis. The amount of platinum in the dialysate collected from tumour and non-tumour brain tissues was determined by atomic absorption spectrophotometry, as representative of cisplatin. Total and free platinum concentrations in plasma were also measured. Free platinum is accumulated preferentially in the tumour tissue and the brain tumour distribution coefficient (the ratio of brain tumour platinum AUC to plasma free platinum AUC, where AUC is the area under the platinum concentration-time curve) was 0.69, although there was little distribution into normal brain tissue. Drug binding to plasma proteins was 65%. It is concluded that simultaneous microdialysis is an easy and available method for assessing in-vivo local pharmacokinetics and distribution of cisplatin in tumour and non-tumour tissues of the brain.Journal of Pharmacy and Pharmacology 09/1997; 49(8):777-80. · 2.03 Impact Factor