July 25, 2016
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Serious and occasionally fatal hypersensitivity (anaphylactoid) reactions have been reported in patients on penicillin therapy. These reactions are more likely to occur in individuals with a history of penicillin hypersensitivity and/or a history of sensitivity to multiple allergens. There have been reports of individuals with a history of penicillin hypersensitivity who have experienced severe reactions when treated with cephalosporins. Before initiating therapy with any penicillin, careful inquiry should be made concerning previous hypersensitivity reactions to penicillin, cephalosporins, or other allergens. If an allergic reaction occurs, the drug should be discontinued and the appropriate therapy instituted. Serious anaphylactoid reactions require immediate emergency treatment with epinephrine. Oxygen, intravenous steroids, and airway management including intubation, should also be administered as indicated.


General: Penicillin should be used with caution in individuals with histories of significant allergies and/or asthma.

Prescribing Pfizerpen (penicillin g potassium) in the absence of proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

Intramuscular Therapy: Care should be taken to avoid intravenous or accidental intraarterial administration, or injection into or near major peripheral nerves or blood vessels, since such injections may produce neurovascular damage. Particular care should be taken with IV administration because of the possibility of thrombophlebitis.

In streptococcal infections, therapy must be sufficient to eliminate the organism (10 days minimum), otherwise the sequelae of streptococcal disease may occur. Cultures should be taken following the completion of treatment to determine whether streptococci have been eradicated.

The use of antibiotics may result in overgrowth of nonsusceptible organisms. Constant observation of the patient is essential. If new infections due to bacteria or fungi appear during therapy, the drug should be discontinued and appropriate measures taken. Whenever allergic reactions occur, penicillin should be withdrawn unless, in the opinion of the physician, the condition being treated is life threatening and amenable only to penicillin therapy.

Aqueous penicillin G by the intravenous route in high doses (above 10 million units) should be administered slowly because of the adverse effects of electrolyte imbalance from either the potassium or sodium content of the penicillin. Penicillin G potassium contains 1.7 mEq potassium and 0.3 mEq sodium per million units. The patient's renal, cardiac, and vascular status should be evaluated and if impairment of function is suspected or known to exist a reduction in the total dosage should be considered. Frequent evaluation of electrolyte balance, renal and hematopoietic function is recommended during therapy when high doses of intravenous aqueous penicillin G are used.

Laboratory Tests: In prolonged therapy with penicillin, periodic evaluation of the renal, hepatic, and hematopoietic systems is recommended for organ system dysfunction. This is particularly important in prematures, neonates and other infants, and when high doses are used.

Positive Coomb's tests have been reported after large intravenous doses.

Monitor serum potassium and implement corrective measures when necessary.

When treating gonococcal infections in which primary and secondary syphilis are suspected, proper diagnostic procedures, including dark field examinations, should be done before receiving penicillin and monthly serological tests made for at least four months. All cases of penicillin treated syphilis should receive clinical and serological examinations every six months for two to three years.

In suspected staphylococcal infections, proper laboratory studies, including susceptibility tests, should be performed.

In streptococcal infections, cultures should be taken following completion of treatment to determine whether streptococci have been eradicated. Therapy must be sufficient to eliminate the organism (a minimum of 10 days), otherwise the sequelae of streptococcal disease (e.g., endocarditis, rheumatic fever) may occur.

Carcinogenesis, Mutagenesis, Impairment of Fertility: No information on long-term studies are available on the carcinogenesis, mutagenesis, or the impairment of fertility with the use of penicillins.

Pregnancy Category B - Teratogenic Effects: Reproduction studies performed in the mouse, rat, and rabbit have revealed no evidence of impaired fertility or harm to the fetus due to penicillin G. Human experience with the penicillins during pregnancy has not shown any positive evidence of adverse effects on the fetus. There are, however, no adequate and well controlled studies in pregnant women showing conclusively that harmful effects of these drugs on the fetus can be excluded. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Nursing Mothers: Penicillins are excreted in human milk. Caution should be exercised when penicillin G is administered to a nursing woman.

Pediatric Use: Penicillins are excreted largely unchanged by the kidney. Because of incompletely developed renal function in infants, the rate of elimination will be slow. Use caution in administering to newborns and evaluate organ system function frequently.

This monograph has been modified to include the generic and brand name in many instances.

Last reviewed on RxList: 6/27/2008


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