Warfarin Chloramphenicol

Warfarin sodium Benzal acetophenone Alkofanone Benzaldehyde Butalamlne HCI Chloramphenicol Fenipentol Isocarboxazid Oxacillin sodium Penicillin G benzathine Phenylpropanolamine HCI Tripelennamine Benzaldehyde cyanohydrin Ethotoin... 

Phenytoin interacts widi many different drugp. For example isoniazid, chloramphenicol, sulfonamides, benzodiazepines, succinimides, and cimetidine all increase phenytoin blood levels. The barbiturates, rifampin, theophylline, and warfarin decrease phenytoin blood levels. When administering the hydantoins with meperidine, die analgesic effect of meperidine is decreased. 

Chloramphenicol inhibits hepatic microsomal enzymes that metabolize several drugs. Half-lives are prolonged, and the serum concentrations of phenytoin, tolbutamide, chlorpropamide, and warfarin are increased. Like other bacteriostatic inhibitors of microbial protein synthesis, chloramphenicol can antagonize bactericidal drugs such as penicillins or aminoglycosides. 

Chloramphenicol [NE] Decreased dicumarol metabolism (probably also warfarin). 

Metabolism is almost always an oxidative process. Reductive metabolism is much more limited. Functional groups that are reduced are, naturally, in a higher oxidation state. The more common examples include nitro groups, which are reduced to amines, and ketones, which reduce to alcohols. Chloramphenicol (8.28), an antibiotic that has fallen out of favor because of serious side effects, contains a nitro group that is reduced to the corresponding amine (8.29) (Scheme 8.9).7 Warfarin (Coumadin, 8.30), an anticlotting agent, is at least partially metabolized by reduction of its ketone to an alcohol. 

Interactions Chloramphenicol is able to inhibit some of the hepatic mixed function oxidases and thus can block the metabolism of such drugs as warfarin, phenytoin, tolbutamide and chlorpropamide, thus elevating their concentrations and potentiating their effects. 

Antimicrobials. Aztreonam, cefamandole, chloramphenicol, ciprofloxacin, co-trimoxazole, erythromycin, fluconazole, itraconazole, ketoconazole, metronidazole, miconazole, ofloxacin and sulphonamides (including co-trimoxazole) increase anticoagulant effect by mechanisms that include interference with warfarin or vitamin K metabolism. Rifampicin and griseofulvin accelerate warfarin metabolism (enzyme induction) and reduce its effect. Intensive broad-spectrum antimicrobials, e.g. eradication regimens for Helicobacter pylori (see p. 630), may increase sensitivity to warfarin by reducing the intestinal flora that produce vitamin K. 

An interaction of warfarin with ocular chloramphenicol (5 mg/ml 1 drop qds in each eye), which led to an increase in INR, has been suspected in an 83-year-old white woman (83). The authors suggested that the effect may be due to chloramphenicol inhibition of hepatic microsomal CYP2C9, since the pharmacologically active enantiomer 5-warfarin is metabolized by this enzyme). 

Leone R, Ghiotto E, Conforti A, Velo G. Potential interaction between warfarin and ocular chloramphenicol. Ann Pharmacother 1999 33(1) 114. 

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