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Aminoglycoside-antibiotics



Why Get Tested

To monitor the level of an aminoglycoside antibiotic such as gentamicin tobramycin or amikacin in the blood to ensure adequate dosing and help avoid toxic side effects

When To Get Tested

At regular intervals during treatment with an aminoglycoside

Sample Required

A blood sample drawn from a vein in your arm

Test Preparation Needed

None but timing of the sample for testing is important follow your healthcare provider s directions




Common Questions


This test is used to monitor the level of the prescribed aminoglycoside antibiotic in the blood The most common aminoglycoside antibiotics in the United States are amikacin gentamicin or tobramycin These drugs are used to treat serious bacterial infections Testing is used to ensure that the level of the drug in the blood is sufficient to treat the infection but not so high as to increase the risk of side effects Measurements of blood levels are timed to reflect the highest concentration peak and the lowest concentration trough of the drug These time points are used to evaluate the adequacy of dosing and monitor the clearance of the drug from the body In some cases a dose of the drug is given only once every 24-48 hours called extended-interval or pulse dosing A test of the drug level on a sample taken 6-14 hours after the dose is used to ensure adequate dosing Blood drug levels are used by clinical pharmacists and healthcare providers to calculate the rate at which a person s body clears the drug from their blood These results are then used to determine the appropriate amount of drug and the appropriate timing between doses to assure that the blood concentration is adequate for treating the infection but is not so high as to increase the risk of toxic side effects For additional information on how the test is used see Therapeutic Drug Monitoring

Blood levels of gentamicin tobramycin or amikacin may be monitored under a variety of conditions For example a person s age kidney function overall health and presence of underlying conditions or symptoms of toxicity may be considered in the decision to perform the testing The length of treatment and type of protocol used for dosing can also be factors Monitoring of aminiglycosides may be recommended when a person will be receiving the drug for more than 3 days For interval dosing testing is usually ordered after 2 to 4 doses of the aminoglycoside have been given and when the drug is expected to have reached a relatively stable level in the blood steady state Drug levels then may be measured again every few days or once a week and with any change in the amount or timing of the dose or with change in kidney function With individuals receiving extended interval dosing no steady state of the drug will be achieved Typically a timed random sample is drawn 6 to 14 hours after the dose for testing Tests that evaluate kidney function such as a creatinine test are often performed at regular intervals during treatment with aminoglycosides More frequent aminoglycoside monitoring may be performed for people with impaired kidney function renal insufficiency and for people who have an increased risk of toxic side effects such as those taking other drugs known to adversely affect hearing and the kidneys ototoxic or nephrotoxic

When a dose of one of the aminoglycosides is given the level typically rises in the blood to a peak concentration and then falls over time to a lower trough concentration Sometimes these drugs are prescribed using interval dosing in which the subsequent dose is timed to be given in anticipation of the falling level The goal is to have a sufficient amount of drug in each dose to maintain a therapeutic level and kill the bacteria causing the infection The dose and the dosing interval are optimized to give the body enough time to clear most of the drug from the previous dose before the next dose is given This minimizes the risk of complications and helps ensure that an adequate drug level is always maintained in the blood For interval-dosing a trough level of the aminoglycoside below the target level indicates that the person tested is clearing the drug at an adequate rate A peak level within the therapeutic range means there should be sufficient drug in the blood to be effective The target level typically depends on the type of infection and the organ infected A peak concentration below the maximum level indicates that the treated person is at less risk of developing toxic side effects though the person may still experience a complication If the trough and or peak concentration is above the maximum level then the person is at an increased risk of toxicity and the healthcare provider may either alter the dose or alter the dosing schedule For an extended-dose regimen the results can help the healthcare provider decide when to give the next dose In general if the blood level is at the low end of the range the health practitioner may decide to dose every 24 hours If the level is at the higher end indicating that the drug is being cleared more slowly the health practitioner may wait 48 hours before giving the next dose If an individual s infection is not responding to the treatment then the healthcare provider may either continue the drug for a longer period of time or consider other treatment options

Intravenous doses of aminoglycosides are given slowly over about 30 minutes Other forms of aminoglycosides such as eye drops ear drops and inhaled drugs may be used to treat specific types of infections Monitoring is not used in these cases The first aminoglycoside streptomycin was developed in the 1940s and used successfully to treat tuberculosis Its use declined with the introduction of other aminoglycosides Aminoglycosides are cleared from the body by the kidneys thus dosages are modified based upon kidney function Tests that reflect the health of the kidneys such as a creatinine or a creatinine clearance are often ordered prior to the initiation of aminoglycoside therapy and then at intervals to monitor kidney function Risk of toxicity is increased in people who are taking other drugs that affect hearing and the kidneys such as certain diuretics particularly furosemide or NSAIDS nonsteroidal anti-inflammatory drugs such as ibuprofen or naproxen or other antibiotics such as vancomycin Because of the potential for complications extended-interval dosing is not recommended in people who Are elderly older than about 70 years of age Are pregnant or have given birth recently Have renal insufficiency or pre-existing kidney disease Have serious liver disease Have extensive burns Have cystic fibrosis Have a history of impaired hearing and or loss of balance

Although a person may receive intravenous aminoglycoside therapy at home usually administered by a home health professional blood levels cannot be monitored at home The test requires specialized equipment and must be performed in a laboratory The home health professional may draw a blood sample prior to administering the next dose of drug This sample will be sent to a laboratory for analysis

There are risks and benefits associated with almost all drug therapies Aminoglycosides continue to be very effective at killing Gram-negative bacteria and sometimes these drugs are the best alternative for successfully treating serious infections

No not all antibiotics require monitoring Unlike aminoglycosides most antibiotics are not associated with significant side effects that are predictable with drug levels They have a larger therapeutic range in which they are effective Because of this they can be prescribed based upon pre-established dosing schedules