<p>Decreased effects of iron and vitamin B12 in anaemic patients. Phenobarbitone and rifampin reduce efficacy of chloramphenicol. Impairs the action of oral contraceptives.<br />
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Potentially Fatal: Increases the effect of oral anticoagulants, oral hypoglycaemic agents, phenytoin. Avoid concomitant administration with drugs that depress bone marrow function.</p>