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Interpretive Handbook

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Test 80134 :
Penicillin G, Serum

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Penicillin G is used for treatment of infections by gram-positive bacteria such as Entercoccus faecalis, Staphylococcus species, Streptococcus pneumonia, and beta-hemolytic strains of streptococcus. Penicillin G has a wide therapeutic index and dose-dependent toxicity. Target peak serum concentrations vary according to the susceptibility of the organism, ie, the minimum inhibitory concentration.


Routine drug monitoring is not indicated in all patients. Penicillin G is less well absorbed than other beta-lactam antibiotics; thus, this assay may be useful in ensuring adequate oral dosing. Penicillin accumulates in patients with renal failure, and monitoring may be useful to prevent concentration-dependent toxicity.

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring penicillin G therapy to ensure absorption or clearance


Evaluating patient compliance

Interpretation Provides information to assist in interpretation of the test results

Most individuals display optimal response to Penicillin G when peak serum levels (drawn 30-60 minutes after a dose) are between 2.0 mcg/mL and 20.0 mcg/mL. Highly susceptible organisms (minimum inhibitory concentration [MIC] <0.06 mcg/mL) will respond at low penicillin serum concentrations; resistant bacteria require higher drug concentrations, depending on the MIC of the specific organism.


The risk of toxicity increases with serum concentrations >20.0 mcg/mL.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Peak: 2.0-20.0 mcg/mL

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Bryan C, Talwani R, Stinson M: Penicillin dosing for pneumococcal pneumonia. Chest 1997 Dec;112:1657-1664

2. Mandell GL: Principles and Practice of Infectious Diseases. Churchill Livingstone Press, London, 1995

3. Moyer TP: Therapeutic drug monitoring. In Tietz Fundamentals of Clinical Chemistry. Fifth edition. Edited by CA Burtis, ER Ashwood, Philadelphia, WB Saunders Company, 2001, pp 608-635