Drug Interaction Report

MONITOR: Chloramphenicol may inhibit the bactericidal effect of penicillins. Chloramphenicol acts by inhibiting cellular protein synthesis and can change actively growing bacteria into static ones. Since penicillins work by inhibiting cell wall synthesis, their effectiveness may be reduced. In addition, neurologic toxicity may be enhanced. Data have been conflicting, and no antagonism or synergistic effects have been reported.

MANAGEMENT: Until more information is available, this combination should probably be reserved for conditions where it has been found to be efficacious and avoided in situations where bactericidal activity is necessary, such as in bacterial meningitis or staphylococcal endocarditis. If the combination is necessary, some experts recommend administering the penicillin several hours before the chloramphenicol. Patients should be closely monitored for altered antimicrobial efficacy.

ADJUST DOSING INTERVAL: Certain penicillins may exhibit reduced gastrointestinal absorption in the presence of food. The therapeutic effect of the antimicrobial may be reduced.

MANAGEMENT: The interacting penicillin should be administered one hour before or two hours after meals. Penicillin V and amoxicillin are not affected by food and may be given without regard to meals.