What Factors Affect Sufficient Aminoglycoside Dosing?

Aminoglycoside dosing depends on many variables that include the location of infection treated, along with the age and health of the patient. As side effects of aminoglycosides include possible hearing loss and kidney damage, physicians usually only prescribe this type of antibiotic under circumstances in which alternative medications prove ineffective. Different medications within the classification require different dosages.

The antibiotic group of medications known as aminoglycosides generally destroys bacteria by first compromising the microbe's membrane. After gaining entry into the cell, the drug inhibits protein synthesis by interfering with the 30S ribosome of the genetic material. Researchers also believe that once exposed to aminoglycosides, the body's phagocytic immune cells become more effective at destroying invading bacteria. Aminoglycosides are usually effective in eradicating strains of gram-positive staphylococcus and many gram-negative microbes, including E. coli and salmonella. Aminoglycosides are also effective agents for treating certain types of intestinal bacteria.

Uses of aminoglycosides include the treatment of bone or skin infections, respiratory or urinary tract infections, and infections involving the heart, also called carditis. Doses typically vary among the different aminoglycosides, which include amikacin, gentamicin and tobramycin. In most situations, physicians calculate aminoglycoside dosing for intramuscular (IM) or intravenous (IV) injections as these medications are generally not well absorbed when taken orally. Physicians typically prescribe amikacin at 7.5 mg/kg of body weight, once a day while gentamicin requires a dose of only 2 to 3 mg/kg once a day.

The dose for inhaled gentimicin is 20 mg twice a day, and tobramycin requires 300 mg inhaled twice a day when used for treating respiratory infections. Physicians may prescribe as much as 1,000 mg of an aminoglycoside before abdominal surgeries, to eliminate bacteria commonly found in the gastrointestinal tract. The doses of aminoglycosides generally differ for pediatric and adult patients. Elderly patients require aminoglycoside dosing adjustments as they do not typically eliminate the medication as quickly as younger patients, which may increase the risk of side effects.

If patients with renal, or kidney, insufficiency require this antibiotic, aminoglycoside dosing adjustments may also be necessary. Physicians usually monitor kidney function with blood tests that measure creatinine levels, when patients with renal disease take aminoglycosides, the drug causes cellular destruction in the glomeruli and small tubules of the kidneys. Symptoms associated with kidney impairment might include decreased urine output. Insufficient hydration, taking loop diuretics like furosemide or non-steroidal anti-inflammatory medications while using aminoglycosides also increases the risk of adverse effects.

Another serious side effect of aminoglycosides includes the possibility of developing varying degrees of hearing loss. The medication accumulates in the inner ear and gradually destroys the cells of the fine hairs that stimulate nerves and enable hearing. Patients may initially experience high frequency hearing loss followed by dizziness and nausea as more hair cells extending into more structures become affected. The condition is irreversible and usually requires cochlear implants to correct.