This article is available online at http://dmd.aspetjournals.org ABSTRACT:Incubations with human liver and gut microsomes revealed that the antibiotic, clindamycin, is primarily oxidized to form clindamycin sulfoxide. In this report, evidence is presented that the Soxidation of clindamycin is primarily mediated by CYP3A. This conclusion is based upon several lines of in vitro evidence, including the following. 1) Incubations with clindamycin in hepatic microsomes from a panel of human donors showed that clindamycin sulfoxide formation correlated with CYP3A-catalyzed testosterone 6␤-hydroxylase activity; 2) coincubation with ketaconazole, a CYP3A4-specific inhibitor, markedly inhibited clindamycin S-oxidase activity; and 3) when clindamycin was incubated across a battery of recombinant heterologously expressed human cytochrome P450 (P450) enzymes, CYP3A4 possessed the highest clindamycin S-oxidase activity. A potential role for flavin-containing monooxygenases (FMOs) in clindamycin S-oxidation in human liver was also evaluated. Formation of clindamycin sulfoxide in human liver microsomes was unaffected either by heat pretreatment or by chemical inhibition (e.g., methimazole). Furthermore, incubations with recombinant FMO isoforms revealed no detectable activity toward the formation of clindamycin sulfoxide. Beyond identifying the drug-metabolizing enzyme responsible for clindamycin S-oxidation, the ability of clindamycin to inhibit six human P450 enzymes was also evaluated. Of the P450 enzymes examined, only the activity of CYP3A4 was inhibited (ϳ26%) by coincubation with clindamycin (100 M). Thus, it is concluded that CYP3A4 appears to account for the largest proportion of the observed P450 catalytic clindamycin S-oxidase activity in vitro, and this activity may be extrapolated to the in vivo condition.Clindamycin (methyl 7-chloro-6,7,8-trideoxy-6-[(2S,4R)-1-methyl-4-propylpyrrolidine-2-carboxamido]-1-thio-1-threo-D-galacto-octopyranoside monohydrochloride) is an antibiotic of the "lincosamide" class (Brodasky et al., 1968). The lincosamide antibiotics seem to be most useful against the bacteria classified as Gram-positive cocci. In addition, clindamycin is helpful against protozoans such as Toxoplasma and Mycoplasma as well as many anaerobic bacteria (Luft and Remington, 1988;Dannemann et al., 1991;Mazur et al., 1999).In humans, absorption of clindamycin is rapid and virtually complete (90%) following oral administration (DeHaan et al., 1972;Metzler et al., 1973). Concentrations of clindamycin in the serum increase linearly with increased dose, and levels exceed the minimum inhibitory concentration for most indicated organisms for at least 6 h following administration of the recommended dose. Clindamycin is widely distributed throughout the body and has an average biological half-life of 2.4 h. The major bioactive metabolites excreted in urine and feces are clindamycin sulfoxide and N-desmethylclindamycin (Seaberg et al., 1984;Flaherty et al., 1988;Gatti et al., 1998).To date, there are no published reports tha...

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A new and promising group of antibacterial agents, collectively known as the oxazolidinones and exemplified by linezolid (PNU-100766, marketed as Zyvox), have recently emerged as important new therapeutic agents for the treatment of infections caused by Gram-positive bacteria. Because of their significance, extensive synthetic investigations into the structure-activity relationships of the oxazolidinones have been conducted at Pharmacia. One facet of this research effort has focused on the identification of bioisosteric replacements for the usual oxazolidinone A-ring. In this paper we describe studies leading to the identification of antibacterial agents incorporating a novel isoxazoline A-ring surrogate. In a gratifying result, the initial isoxazoline analogue prepared was found to exhibit in vitro antibacterial activity approaching that of the corresponding oxazolidinone progenitor. The synthesis and antibacterial activity profile of a preliminary series of isoxazoline analogues incorporating either a C-C or N-C linkage between their B- and C-rings will be presented. Many of the analogues exhibited interesting levels of antibacterial activity. The piperazine derivative 54 displayed especially promising in vitro activity and in vivo efficacy comparable to the activity and efficacy of linezolid.

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