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Interpretive Handbook

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Test 81750 :
Gentamicin, Random, Serum

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

Gentamicin is an antibiotic used to treat life-threatening blood infections caused by gram-negative bacilli, particularly Citrobacter freundii, Acinetobacter species, Enterobacter species, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Providencia stuartii, Pseudomonas aeruginosa, and Serratia species. It is often used in combination with beta-lactam therapy.

 

A gentamicin minimal inhibitory concentration (MIC) of < or =4.0 mcg/mL is considered susceptible for gram-negative bacilli. A MIC of < or =500 mcg/mL is considered synergistic when combined with appropriate antibiotics for treatment of serious enterococcal infections.

 

Conventional dosing of gentamicin is usually given 2 to 3 times per day by intravenous or intramuscular injections in doses to achieve peak blood concentration between 5.0 to 12.0 mcg/mL depending on the type of infections. Gentamicin also may be administered at higher doses (usually 5-7 mg/kg) once per day to patients with good renal function (known as pulse dosing). Dosing amount or interval must be decreased to accommodate for reduced renal function.

 

Ototoxicity and nephrotoxicity are the primary toxicities associated with gentamicin. This risk is enhanced in presence of other ototoxic or nephrotoxic drugs. Monitoring of serum levels and symptoms consistent with ototoxicity is important. For longer durations of use, audiology/vestibular testing should be considered at baseline and periodically during therapy.

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

Monitoring adequacy of serum concentration during gentamicin therapy

 

This unit code is used whenever a specimen is submitted or collected without collection timing information

Interpretation Provides information to assist in interpretation of the test results

Goal peak concentrations levels depend on the type of infection being treated. Goal trough levels should be <2.0 mcg/mL. Peak targets are generally between 5.0 and 12.0 mcg/mL for conventional dosing. Prolonged exposure to either peak levels exceeding 12.0 mcg/mL or to trough levels exceeding 2.0 mcg/mL may lead to toxicity.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

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.

GENTAMICIN, PEAK

5.0-12.0 mcg/mL

 

GENTAMICIN, TROUGH

<2.0 mcg/mL

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

1. Hammett-Stabler CA, Johns T: Laboratory Guidelines for Monitoring of Antimicrobial Drugs. Clin Chem 1998;44(5):1129-1140

2. Moyer TP: Therapeutic drug monitoring. In Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER  Ashwood, Philadelphia, WB Saunders Company, 2006

3. Wilson JW, Estes LL: Mayo Clinic Antimicrobial Therapy Quick Guide. Mayo Clinic Scientific Press and Information Healthcare USA, 2008


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