RECUCED EFFICACY OF ORAL CONTRACEPTIVES. PROBENECID DECREASES THE RENAL TUBULAR SECRETION OF AMOXICILLIN. CONCURRENT USE WITH AMOXICILLIN MAY RESULT IN INCREASED AND PROLONGED BLOOD LEVELS. CHLORAMPHENICOL, ERYTHROMYCINS, SULFONAMIDES, AND TETRACYCLINES MAY INTERFERE WITH THE BACTERICIDAL EFFECTS OF PENICILLIN, THE CLINICAL SIGNIFICANCE OF THIS INTERACTION IS NOT WELL DOCUMENTED.