Which of the following is not an established antimicrobial drug synergism at the clinical level?: (A) Amphotericin B and flucytosine in cryptococcal meningitis, (B) Carbenicillin and gentamicin in pseudomonal infections, (C) Penicillin and tetracycline in bacterial meningitis, (D) Trimethoprim and sulfamethoxazole in coliform infections
Answer is C. Combination of a bacteriostatic and a bactericidal drug in most cases is antagonistic. Bactericidal drugs act on fast multiplying organisms whereas bacteriostatic drugs inhibit the growth. Here, penicillin is bactericidal whereas tetracyclines are bacteriostatic.