ExperimentalSurgery3

Antibiotic Guidelines

General Recommendations

Selection

If a culture and sensitivity is not available, select antibiotics based on probable organism and probable sensitivity. For example, normal skin flora are usually Gram +, so for a a skin incision, select something with a Gram + spectrum, e.g., amoxicillin/clavulanate or a potentiated sulfonamide. If GI surgery is performed, an antibiotic with a Gram - spectrum is more appropriate, e.g. an aminoglycoside or ceftiofur. Indwelling catheters tend to become infected with skin or fecal contaminants, including anaerobes. Thus a broad spectrum and anaerobic spectrum is required, e.g. amoxicillin/clavulanate, ceftiofur or ticarcillin. Pseudomonas is an opportunist with a high likelihood of a multiple antibiotic resistance phenotype. An extended spectrum penicillin (ticarcillin), a fluoroquinolone (enrofloxacin) or an aminoglycoside (amikacin) may be necessary.

Combinations

Antibiotic activity is classified as being either bacteriostatic (inhibits cells from dividing) or bacteriocidal (kills bacteria even if they are not dividing).  In general, combining two bacteriostatic drugs results in additive effect, combining two cidal drugs results in synergistic effect. Combining cidal and static agents can result in impairment of bacteriocidal activity. If you are treating a specific infection, select two drugs with activity against the organism in question. If you are looking for broad spectrum activity, select drugs with complementary activity, eg. penicillin and an aminoglycoside, or enrofloxacin and clindamycin.

Dosages

Dosages for antibiotics and a description of their activities are listed in RAR's drug formulary.