Pharmacokinetics of a high dose of gentamicin administered intravenously or intramuscularly to horses.

The research article explores the pharmacokinetics of administering a high intravenous or intramuscular dose of gentamicin to horses, suggesting that single, daily doses may be as safe and effective as multiple doses given daily according to traditional lower-dose routines.

Study Design

• The study was a repeated-measures investigation involving six clinically normal adult female stock-type horses. The repeated-measures design allows for repeated observations over time and can provide more detailed information about changes and responses to interventions.
• The objective was to understand the pharmacokinetics, or how the drug moves within the body, when a high dose of gentamicin is administered either intravenously (i.v.) or intramuscularly (i.m.). Gentamicin, an antibiotic, was administered at a dose of 6.6 mg/kg of body weight for both routes in a two-way cross-over design, meaning that the same horses received the drug both ways at different times.
• The researchers measured serum gentamicin concentrations over a 24-hour period after administration.

Results

• The plasma concentration curves aligned with a two-compartment model, suggesting the drug distributes first throughout the bloodstream before moving into tissues.
• The highest plasma gentamicin concentrations were 71.9 +/- 15.7 micrograms/ml immediately after the i.v. injection and 22.0 +/- 4.9 micrograms/ml (1.31 hours after administration) for the i.m. group.
• The areas under the curve (AUC, a pharmacokinetic measure of total drug exposure over time) were markedly similar for both administration routes (116.6 +/- 14.5 and 116.3 +/- 14.6 micrograms.h/ml for the i.v. and i.m. groups, respectively).
• The elimination half-life for the intravenous group was 3.0 +/- 2.8 hours, suggesting quick clearance from the bloodstream.
• Trough concentrations (the minimum concentration before the next dose) were 15 and > 12 hours for the i.v. and i.m. groups, respectively.
• The study did not detect significant changes in clinicopathologic variables before and after administration of gentamicin, indicating the high dose did not produce observable adverse effects.

Conclusions

• The administration of a high dose of gentamicin, whether i.v. or i.m., resulted in observable peak plasma concentrations, AUC, and minimum trough plasma concentrations.
• The study’s results suggest that once-daily administration of gentamicin could be as efficacious and safe as multiple-dose daily administration, in line with traditional low-dose regimens.
• This administration protocol could potentially align more closely with those used in other species, thus offering a one-size-fits-all approach to antibiotic administration.