Gentamicin Oral Formulation Availability
Gentamicin is NOT available in a clinically useful oral formulation for systemic infections due to extremely poor oral bioavailability. The drug must be administered intravenously (IV) or intramuscularly (IM) for therapeutic effect 1.
Route of Administration
Gentamicin is administered exclusively via IV or IM routes for treatment of systemic infections including endocarditis, staphylococcal infections, and gram-negative bacterial infections 1.
The standard dosing is 3 mg/kg/day IV or IM in 2 or 3 divided doses for most indications, with duration varying by infection type (typically 3-5 days for adjunctive therapy in endocarditis) 1.
Why Oral Gentamicin Fails
Gentamicin is a polarized, water-soluble aminoglycoside with extremely poor intestinal membrane permeability, resulting in negligible oral bioavailability 2.
Even experimental oral formulations using absorption enhancers (labrasol) in animal studies achieved only minimal systemic absorption, with Cmax values of 2.38 μg/ml compared to therapeutic IV levels of 10-12 μg/ml needed for efficacy 2.
The low oral bioavailability means orally administered gentamicin remains in the gastrointestinal tract and does not achieve therapeutic serum concentrations 2.
Clinical Implications
All major guidelines specify IV or IM administration only for gentamicin in treating endocarditis, staphylococcal infections, and other systemic bacterial infections 1.
Therapeutic drug monitoring (TDM) is essential when gentamicin is used, targeting trough concentrations <1 mg/L (preferably <0.5 mg/L) to minimize nephrotoxicity and ototoxicity 1, 3.
Peak serum concentrations should reach 3-4 μg/mL (when given in divided doses) or 10-12 μg/mL (when given as once-daily dosing) to ensure efficacy 1, 3.
Important Caveat
- While oral gentamicin has been studied experimentally for selective gut decontamination, this is NOT for systemic infection treatment and the drug remains in the intestinal lumen without systemic absorption 2.