Micro winter lecture final

Chloramphenicol works against everything but unfortunately it causes aplastic anemia in 1 out of about every 24,000 to 40,000 patients. It's still good enough for government work though -- in third world countries (it helps that it can be given orally). In the US, chloramphenicol is only first line for meningitis when there are known severe allergies to penicillins AND cephalosporins; and for Rickettsial diseases (think Rocky Mountain Spotted Fever) in children or pregnant women.

Imipenem also works against everything, with the notable exception of MRSA. It is degraded renally by dihydropeptidase I (co-administer cilastatin) and excreted renally (reduce dose in renal failure). Meropenem is an improved version that is resistant to dihydropeptidase. Unfortunately, the carbepenems are limited in their use by CNS toxicity: they can cause seizures, though meropenem is better in this respect. They are also cross-allergenic with penicillin. They are first-line therapy for Enterobacter. Ertapenem, a newer carbepenem that only requires once daily I.V. administration, is the drug of choice for severe, polymicrobic diabetic foot infections.

Vancomycin works against all gram positive organisms, with the notable exception of VRE (resistance when D-ala D-ala becomes D-ala D-lac). The main indications for use are endocarditis, line sepsis, and meningitis -- think severe, nosocomial infections where MRSA coverage is crucial. Vancomycin is generally well tolerated (some nephrotoxicity, ototoxicity, thrombophlebitis, IgE-mediated "red man syndrome" if administered by I.V. too fast) but these side effects pale in comparison to the severe situations that actually warrant its use. Vancomycin could be used more broadly, but it's generally held in reserve as an ace card to prevent development of more widespread resistance.

Aztreonam, a monobactam, works against all gram negative organisms, with the notable exception of gram-negative anaerobes. Like other beta lactam antibiotics, they are synergistic with aminoglycosides. However, they are less nephrotoxic than aminoglycosides and can be used as a solo alternative in severe gram negative rod infections. They can also be used if the patient is allergic to penicillins, as unlike cephalosporins and carbepenems, monobactams are not cross-allergenic with penicillin. Monobactams are generally well-tolerated: the only main side effect is occasional GI upset.

Penicillin is first line for beta-hemolytic strep (long-acting IM benzathine penicillin for strep pharyngitis) and syphilis; less high yield -- Actinomyces israelii, and Leptospira interrogans. Penicillin may also be useful against alpha-hemolytic strep like Viridans strep and pneumococcus (latter now displays intermediate-level resistance to penicillin).

Penicillinase-resistant penicillins. Methicillin is no longer used due to interstial nephritis. Use nafcillin for MSSA; use "naf" for staph. Use dicloxacillin (can be given orally) for outpatient empiric treatment of infected skin wound.

Aminopenicillins are penicillinase-sensitive and therefore administered with clavulanic acid. Amoxicillin (oral) is used for outpatient treatment of bronchitis, otitis media, and sinusitis. Ampicillin combined with gentamicin is a combo used for broad empiric coverage (surgery, serious urinary tract infections). Amp-gent also treats enterococcal infections, which are resistant to most penicillin and cephalosporins. Ampicillin also covers Listeria, and is added empirically in meningitis for neonates, the elderly, and the immunocompromised.

Anti-pseudomonals: ticarcillin, carbenecillin, piperacillin.

Actinomyces is resistant to metronidazole; use penicillin. Use TMP-SMX for Nocardia.

First line therapy for meningitis is ceftriaxone and Vancomycin.

Normal flora: Candida; Viridans, Enteroccoci, GBS in women; S. epidermidis; Acinetobacter (only gram negative skin flora), Bacteroides, Fusobacterium, Actinomyces, Pseudomonas, a lot of other Enterobactericiae