Gentamicin

Gentamicin is part of the drug class:

• Other aminoglycosides

Tell your doctor about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

• other antibiotics such as amoxicillin (Amoxil, Larotid, Moxatag, in Augmentin, in Prevpac), ampicillin, or penicillin
• dimenhydrate (Dramamine)
• meclizine (Bonine)
• nonsteroidal anti-inflammatory drugs such as indomethacin (Indocin, Tivorbex)

This is not a complete list of gentamicin drug interactions. Ask your doctor or pharmacist for more information.

Take gentamicin exactly as prescribed.

Topical:

This medication comes in solution form to be instilled into the eye and in ointment form to be applied to the eyes. For eye infections, gentamicin solution is usually used every 4 to 8 hours and the ointment is applied 2 to 4 times a day.

Gentamicin is also available as a cream and an ointment for topical application to the skin. It is applied to skin lesions or infections 3 to 4 times a day.

If you miss a dose, take the missed dose as soon as you remember. If it is almost time for the next dose, skip the missed dose and take your next dose at the regular time. Do not take two doses of gentamicin at the same time.

Injectable:

Gentamicin is also available in an injectable form to be given directly into a vein (IV) or a muscle (IM) by a healthcare professional.

If you take too much gentamicin, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

If gentamicin is administered by a healthcare provider in a medical setting, it is unlikely that an overdose will occur. However, if overdose is suspected, seek emergency medical attention.

Topical:

Store gentamicin creams, ointments, and eye drops at room temperature.

Injectable:

Store gentamicin for injection in the freezer or refrigerator.

Keep this and all medicines out of the reach of children.

Injectable:

BOXED WARNINGS

Patients treated with aminoglycosides should be under close clinical observation because of the potential toxicity associated with their use.

As with other aminoglycosides, gentamicin injection is potentially nephrotoxic. The risk of nephrotoxicity is greater in patients with impaired renal function and in those who receive high dosage of prolonged therapy.

Neurotoxicity manifested by ototoxicity, both vestibular and auditory, can occur in patients treated with gentamicin, primarily in those with pre-existing renal damage and in patients with normal renal function treated with higher doses and/or for longer periods than recommended. Aminoglycoside-induced ototoxicity is usually irreversible. Other manifestations of neurotoxicity may include numbness, skin tingling, muscle twitching and convulsions.

Renal and eighth cranial nerve function should be closely monitored, especially in patients with known or suspected reduced renal function at onset of therapy and also in those whose renal function is initially normal but who develop signs of renal dysfunction during therapy. Urine should be examined for decreased specific gravity, increased excretion of protein and the presence of cells or casts. Blood urea nitrogen (BUN), serum creatinine or creatinine clearance should be determined periodically. When feasible, it is recommended that serial audiograms be obtained in patients old enough to be tested, particularly high-risk patients. Evidence of ototoxicity (dizziness, vertigo, tinnitus, roaring in the ears or hearing loss) or nephrotoxicity requires dosage adjustment or discontinuance of the drug. As with the other aminoglycosides, on rare occasions changes in renal and eighth cranial nerve function may not become manifest until soon after completion of therapy.

Serum concentrations of aminoglycosides should be monitored when feasible to assure adequate levels and to avoid potentially toxic levels. When monitoring gentamicin peak concentrations, dosage should be adjusted so that prolonged levels above 12 mcg/mL are avoided. When monitoring gentamicin trough concentrations, dosage should be adjusted so that levels above 2 mcg/mL are avoided. Excessive peak and/or trough serum concentrations of aminoglycosides may increase the risk of renal and eighth cranial nerve toxicity.

In the event of overdosage or toxic reactions, hemodialysis may aid in the removal of gentamicin from the blood, especially if renal function is, or becomes, compromised. The rate of removal of gentamicin is considerably lower by peritoneal dialysis than it is by hemodialysis.

In the newborn infant, exchange transfusions may also be considered.

Concurrent and/or sequential systemic or topical use of other potentially neurotoxic and/or nephrotoxic drugs, such as cisplatin, cephaloridine, kanamycin, amikacin, neomycin, polymyxin B, colistin, paromomycin, streptomycin, tobramycin, vancomycin and viomycin, should be avoided. Other factors which may increase patient risk of toxicity are advanced age and dehydration.

The concurrent use of gentamicin with potent diuretics, such as ethacrynic acid or furosemide, should be avoided, since certain diuretics by themselves may cause ototoxicity. In addition, when administered intravenously, diuretics may enhance aminoglycoside toxicity by altering the antibiotic concentration in serum and tissue.

Aminoglycosides can cause fetal harm when administered to a pregnant woman.

Call your doctor for instructions if you miss a dose of gentamicin.

Applies to gentamicin: compounding powder, injectable solution, intravenous solution

General

The most frequently reported adverse effects associated with gentamicin therapy are ototoxicity and nephrotoxicity. These forms of toxicity occur more frequently in patients who experience prolonged exposure to serum gentamicin trough concentrations of greater than 2 mcg/mL. Patients with renal insufficiency are at an increased risk of developing toxicity.[Ref]

Renal

Acute renal failure due to gentamicin is usually nonoliguric with an average rise in serum creatinine of 1 to 3 mg/dL. Renal function generally returns to baseline in 7 to 14 days. Rarely, gentamicin produces renal tubular acidosis and renal potassium and magnesium wasting. There is no relationship between acute renal failure and the daily dose of gentamicin, however, an increased incidence has been associated with a serum trough gentamicin concentration greater than 2 mcg/mL. It has been suggested that there is a correlation between the higher peak concentrations associated with once-daily dosing and a higher incidence of nephrotoxicity. Other predisposing factors include advanced age, preexisting renal insufficiency, dehydration, and concomitant use of other potentially nephrotoxic drugs.[Ref]

Renal side effects associated with gentamicin use have included nephrotoxicity. The overall incidence of aminoglycoside nephrotoxicity is 2% to 10%. Gentamicin nephrotoxicity occurs in two forms: acute renal failure (ARF), and a more gradual, transient, and reversible azotemia. Fanconi syndrome and Bartter-like syndrome have been reported.[Ref]

Nervous system

The onset of ototoxicity may be asymptomatic or may manifest as dizziness, vertigo, ataxia, tinnitus, and roaring in the ears. High tone hearing loss is often an early symptom of auditory toxicity. It has been suggested that once-daily dosing of gentamicin is associated with a higher incidence of ototoxicity.

Other side effects possibly related to gentamicin have included lethargy, confusion, depression, headache, pseudotumor cerebri, and acute organic brain syndrome.[Ref]

Nervous system side effects have included ototoxicity, which generally presents as loss of vestibular function secondary to hair cell damage, but may also be auditory. Ototoxicity is closely related to the development of renal impairment, and may be irreversible. Peripheral neuropathy or encephalopathy with numbness, skin tingling, muscle twitching, seizures, and myasthenia gravis-like syndrome have also been reported.

Intraventricular and intrathecal administration of gentamicin has rarely been associated with aseptic meningitis, transient hearing loss, and seizures. Neuromuscular side effects including ataxia, paresis and incontinence have been reported after large intrathecal doses (40 mg to 160 mg) of preservative-containing gentamicin. Concurrent administration of parenteral and intrathecal gentamicin has been associated with eighth nerve dysfunction, fever, convulsions, leg cramps, and increases in cerebrospinal fluid protein.[Ref]

Musculoskeletal

Musculoskeletal side effects have rarely included neuromuscular blockade, which occurs most commonly in patients who are predisposed including patients with myasthenia gravis, hypocalcemia, and those receiving a concomitant neuromuscular blocking agent. Tetany and muscle weakness may be associated with gentamicin-induced hypomagnesemia, hypocalcemia, and hypokalemia. Joint pain has also been reported.[Ref]

Respiratory

Respiratory side effects have included case reports of respiratory depression and respiratory arrest. Gentamicin has also been possibly associated with pulmonary fibrosis.[Ref]

Hypersensitivity

Hypersensitivity reactions possibly associated with gentamicin have included anaphylactoid reactions and laryngeal edema. Suspected allergic reactions against gentamicin with sodium metabisulfite preservative have been reported.[Ref]

Local

Local reactions have occasionally included pain at the injection site, and rarely subcutaneous atrophy or fat necrosis at the injection site. Reactions associated with intrathecal injections have included arachnoiditis and burning at the injection site.[Ref]

Dermatologic

Dermatologic side effects possibly associated with gentamicin have included rash, itching, urticaria, generalized burning, and alopecia.[Ref]

Hematologic

Hematologic side effects possibly related to gentamicin use have included anemia, leukopenia, granulocytopenia, transient agranulocytosis, eosinophilia, increased and decreased reticulocyte counts, thrombocytopenia, immunologic thrombocytopenia, and purpura.[Ref]

Hepatic

Hepatic side effects possibly related to gentamicin use have included transient hepatomegaly, and increases in serum transaminase, serum LDH, and bilirubin.[Ref]

Cardiovascular

Cardiovascular side effects possibly related to gentamicin have included hypotension and hypertension.[Ref]

Gastrointestinal

Gastrointestinal side effects possibly related to gentamicin have included nausea, vomiting, weight loss, decreased appetite, increased salivation, and stomatitis.[Ref]

Ocular

Ocular side effects have included case reports of retinal ischemia resulting in loss of visual acuity after inadvertent intraocular injection of massive doses of gentamicin.[Ref]

Other

Other side effects possibly related to gentamicin have included transient splenomegaly and fever.[Ref]

Pyrogenic reactions with symptoms of shaking, chills, fever, rigors, tachycardia, and/or hypotension have been reported with intravenous gentamicin. These reactions generally occurred within 3 hours of administration and were believed to be due to once-daily gentamicin doses delivering sufficient endotoxin over one hour to be pyrogenic.[Ref]

Some side effects of gentamicin may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.