MEDizzy - A patient with a P. aeruginosa infection is receiving

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Anti Infectives

A patient with a P. aeruginosa infection is receiving intravenous gentamicin. The aminoglycoside blood levels are well above the minimum inhibitory concentration (MIC), but the clinical response is not satisfactory. A new medication order calls for adding penicillin, administered in a separate IV line to avoid a physical incompatibility. If this order is carried out, which of the following is most likely to occur?

ExplanationThe rationale behind this combination is that penicillins essentially weaken the cell walls of susceptible bacteria, which in turn facil- itates access of the aminoglycoside to its site of action, the bacterial ribo- somes. This usually provides better antibiotic response than with either antibiotic used alone, and with the aminoglycoside, serum levels aren’t necessarily so high that they are more likely to cause ototoxicity, nephro- toxicity, or other adverse responses. You should also recall at least two other things: (1) the penicillin in this combination is usually an extended-spectrum penicillin, such as ticar- cillin, and (2) as we have specifically noted in the question, the adminis- tration of these drugs is by separate IV lines. That is because if the two drugs were mixed together in sufficiently high concentrations, the peni- cillin may chemically inactivate the gentamicin.