Decreased renal tubular secretion w/ probenecid. Aminoglycoside by any of the aminopenicillins. Ampicillin: Increased incidence of rashes w/ allopurinol. Substantial mutual inactivation (in vitro
) w/ aminoglycosides (administer at separate sites at least 1 hr apart). Additive effects in the alteration of platelet aggregation & coagulation tests w/ anticoagulants. Bactericidal effects may be interfered by bacteriostatic drugs (eg, chloramphenicol, erythromycin, sulfonamides & tetracyclines). May reduce effects of estrogen-containing OCs. May decrease clearance of methotrexate & increase methotrexate toxicity. A transmit decrease in plasma conc of total conjugated estrone & estradiol.