The effect of fluconazole and ketoconazole on the metabolism of sulphamethoxazole

Abstract

1 Cytochrome P450-mediated bioactivation of sulphamethoxazole to a hydroxylamine has been implicated in the hypersensitivity reactions associated with co-trimoxazole administration. Inhibiting the formation of the hydroxylamine may be one method of preventing the high frequency of toxicity which is observed in HIV-infected patients. Therefore, in this study, we have investigated the ability of fluconazole and ketoconazole, known cytochrome P450 inhibitors, to inhibit the formation of sulphamethoxazole hydroxylamine. 2 Ten healthy male volunteers were given co-trimoxazole (800 mg sulphamethoxazole and 160 mg trimethoprim) alone or 1 h after either fluconazole ( 150 mg) or ketoconazole (200 mg) in a randomized fashion with a washout period of at least 1 week between each phase. Urine was collected for 24 h, and sulphamethoxazole and its metabolites were quantified by electrospray LC-MS. 3 Ketoconazole had no effect on the urinary recovery of sulphamethoxazole or any of its metabolites. In contrast, fluconazole significantly (P<0.001) inhibited the formation of sulphamethoxazole hydroxylamine by 50.0±15.1%. Fluconazole also inhibited the oxidation of sulphamethoxazole to the 5-methylhydroxy and 5-methylhydroxy acetate metabolites by 69.9±15.8% and 64.0±12.0%, respectively, but had no effect on the amount of sulphamethoxazole, N 4 -acetyl sulphamethoxazole, or sulphamethoxazole N 1 -glucuronide excreted in urine. 4 The potential clinical benefit of using fluconazole to prevent hypersensitivity to co-trimoxazole in patients with AIDS needs to be assessed in a prospective study using both metabolite formation and the clinical occurrence of adverse reactions as end-points.

Sulfamethoxazole and Its Metabolite Nitroso Sulfamethoxazole Stimulate Dendritic Cell Costimulatory Signaling

“…CYP2C9 and MPO, consistent with previous literature (10,11,62), but also CYP2C8, were found to be capable of SMX-NHOH generation (Table I). All other enzymes studied were inactive.…”

Nonenzymatic Formation of a Novel Hydroxylated Sulfamethoxazole Derivative in Human Liver Microsomes: Implications for Bioanalysis of Sulfamethoxazole Metabolites

“…Although it was claimed that cyclooxygenase could also N-hydroxylate SMX, a recent study found that the oxidation of SMX in cyclooxygenase incubations containing ascorbate was due to H 2 O 2 in the reaction mixture (Vyas et al, 2006). It is noteworthy that, in the context of the present observations, accurate quantification of a hydroxylamine in vitro (Cribb and Spielberg, 1990a) and in vivo (Gill et al, 1996;Winter et al, 2004) requires the loss of analyte through autoxidation to be blocked with a reducing agent; ascorbate being the agent of choice. In addition, identification of the hydroxylamine has often depended upon cochromatography with an authentic standard using relatively simple high-performance liquid chromatography (HPLC) conditions.…”

“…This is believed to be an idiosyncratic consequence of enzymatic generation of the hydroxylamine metabolite (SMX hydroxylamine; SMX-NHOH) and subsequent autoxidation to a protein-reactive nitroso species (Cribb et al, 1991). The cellular distribution (Naisbitt et al, 1999), cytotoxicity (Vyas et al, 2005;Lavergne et al, 2006), and immunogenicity (Naisbitt et al, 2001) of SMX metabolites have been studied extensively.SMX-NHOH formation has been found both in hepatic microsomes (Cribb and Spielberg, 1990a;Cribb et al, 1995) and in vivo (Cribb and Spielberg, 1992;Gill et al, 1996). Metabolism of SMX to SMX-NHOH is catalyzed by human hepatic CYP2C9 (Cribb et al, 1995;Gill et al, 1999) and neutrophilic myeloperoxidase (Cribb et al, 1990).…”

“…SMX-NHOH formation has been found both in hepatic microsomes (Cribb and Spielberg, 1990a;Cribb et al, 1995) and in vivo (Cribb and Spielberg, 1992;Gill et al, 1996). Metabolism of SMX to SMX-NHOH is catalyzed by human hepatic CYP2C9 (Cribb et al, 1995;Gill et al, 1999) and neutrophilic myeloperoxidase (Cribb et al, 1990).…”

“…Three published chromatographic protocols were used to attempt to separate the novel hydroxylated species from an authentic SMX-NHOH standard, both to try to identify suitable conditions for analysis and to determine whether any previous studies may have failed to adequately separate the two compounds. Samples were eluted from the following: 1) a Prodigy 5-m ODS-2 column (150 ϫ 4.6 mm; Phenomenex, Macclesfield, Cheshire, UK) using an isocratic mobile phase of glacial acetic acid (1% v/v) and acetonitrile (20% v/v) in water at a flow rate of 1 ml/min (Gill et al, 1996); 2) an Ultrasphere 5-m C-18 column (150 ϫ 4.6 mm; Beckman Coulter, High Wycombe, Buckinghamshire, UK) using an isocratic mobile phase of acetonitrile (25% v/v), glacial acetic acid (1% v/v), and triethylamine (0.05% v/v) in water at a flow rate of 1 ml/min (Cribb and Spielberg, 1990a); and 3) a Nova-pak 4-m C-18 column (150 ϫ 3.9 mm; Waters, Elstree, Hertfordshire, UK) using a isocratic mobile phase of acetonitrile (18.95% v/v), glacial acetic acid (1% v/v), and triethylamine (0.05% v/v) in water at a flow rate of 1 ml/min (Coleman et al, 1989;Vyas et al, 2006). Complete resolution of the hydroxylated SMX derivatives was achieved with an Ultrasphere 5-m C18 column (250 ϫ 4.6 mm; Beckman Coulter) using 10% acetonitrile in 50 mM formic acid for 5 min, 10 to 70% acetonitrile over 20 min, and 70 to 100% acetonitrile over 2 min (method 4).…”