Ho JW, Moody DE. Determination of tolbutamide hydroxylation in rat liver microsomes by high-performance liquid chromatography: effect of psychoactive drugs on in vitro activity.
Life Sci 1993;
52:21-8. [PMID:
8417276 DOI:
10.1016/0024-3205(93)90284-a]
[Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A simplified HPLC method for tolbutamide metabolism to hydroxytolbutamide has been used to screen sixty psychoactive drugs for their ability to inhibit rat liver microsomal tolbutamide hydroxylation. One-step extraction with diethyl ether was followed by reconstitution and isocratic HPLC analysis with a binary mobile phase (ammonium phosphate:methanol, 45:55, v/v). Nanogram amounts of hydroxytolbutamide formation were estimated with UV detection at 240 nm. Hydroxytolbutamide formation was linear with incubation times of 40-120 min, but specific activity increased with increases in microsomal protein (0.15-1.10 mg). A differential inhibitory response was demonstrated for tolbutamide and debrisoquine hydroxylation to 5 psychoactive drugs, suggesting that tolbutamide hydroxylation is not dependent on P4502D1. Sixty psychoactive drugs, or drug metabolites, (at 33 microM) were then co-incubated with tolbutamide (at 2.5 and 10.2 microM). Tolbutamide hydroxylation was refractory (< 25% inhibition) to twenty-four of the drugs and only mildly inhibited (25-50% inhibition) by twenty-eight. Two compounds, trans-3-methylfentanyl and flurazepam, produced > 50% inhibition that was independent of tolbutamide concentration. Five of the drugs (methadone, chlorpheniramine, meperidine, 6-monoacetylmorphine and methylphenidate), however, caused greater than 50% inhibition in a competitive manner which suggests these drugs may share an affinity for the substrate binding site for tolbutamide.
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