Inhibition by atovaquone of CYP2C9-mediated sulphamethoxazole hydroxylamine formation.
Article Details
- CitationCopy to clipboard
Miller JL, Trepanier LA
Inhibition by atovaquone of CYP2C9-mediated sulphamethoxazole hydroxylamine formation.
Eur J Clin Pharmacol. 2002 Apr;58(1):69-72. doi: 10.1007/s00228-002-0424-y. Epub 2002 Mar 7.
- PubMed ID
- 11956677 [ View in PubMed]
- Abstract
OBJECTIVE: To determine whether the antiprotozoal drug atovaquone inhibits the cytochrome P(450) (CYP)2C9-mediated metabolism of sulphamethoxazole (SMX) to its potentially harmful hydroxylamine metabolite (SMX-HA) in vitro. METHODS: Generation of SMX-HA from SMX was measured directly using high-performance liquid chromatography in human liver microsomes or expressed CYP2C9*1, with or without preincubation with reduced nicotinamide adenine dinucleotide phosphate, and the inhibition constant (K(i)) for atovaquone was determined. To determine the effect of protein binding in vitro, in some experiments, atovaquone was pre-incubated with serum proteins, followed by filtration. RESULTS: The K(i) for inhibition of SMX-HA formation by atovaquone was 15 microM, which is within clinically attainable total plasma atovaquone concentrations of 45-55 microM. Atovaquone (45 microM) inhibited SMX-HA formation by 39% in human liver microsomes. However, following preincubation of atovaquone with serum proteins, no inhibitory effect by atovaquone was observed, consistent with previous reports of high plasma protein binding for atovaquone. Compared with human liver microsomes, CYP2C9*1 showed an eightfold greater specific activity for SMX-HA generation; as for liver microsomes, CYP2C9*1 activity was inhibited by atovaquone. CONCLUSIONS: Atovaquone is a relatively weak inhibitor of CYP2C9-mediated SMX-HA formation in vitro. However, the effect is not observed in the presence of serum proteins. It is therefore unlikely that atovaquone would significantly inhibit SMX-HA formation in vivo.
DrugBank Data that Cites this Article
- Drug Enzymes
Drug Enzyme Kind Organism Pharmacological Action Actions Atovaquone Cytochrome P450 2C9 Protein Humans UnknownInhibitorDetails