Pharmacokinetics of gentamicin at steady-state in ponies: serum, urine, and endometrial concentrations.

This research involves understanding how the drug Gentamicin behaves in the body of ponies, in terms of its absorption, distribution, metabolism, and elimination. The study found that to maintain certain levels of Gentamicin in the system, a dosage of 5 mg of the drug for each kg of body weight is recommended every 8 hours.

Study Design

• The research was conducted on 6 healthy mares (female ponies). Each was given a dosage of Gentamicin of 5 mg per kg of their body weight, administered every 8 hours for a week, for a total of 21 doses.
• Venous blood samples were taken from the mares before and one hour after the 5th, 10th, 14th, and 19th doses. This aimed to monitor the levels of the drug in the blood at different stages of treatment – before the dose (trough) and after the dose (peak).
• Endometrial biopsies were also conducted on the fourth and seventh days. Urine was collected 24 hours after catheterization on Day 7. Serum, urine, and endometrial Gentamicin concentrations were measured using a radioimmunoassay technique.

Results

• It was found that the data obtained from the terminal phase were best fitted by a one-compartment open model with a half-life of 2.13 +/- 0.43 hours. This shows how quickly the drug is metabolized and eliminates from the body.
• The total body clearance and renal clearance rates were calculated to be 1.69 +/- 0.41 ml/min/kg and 1.40 +/- 0.26 ml/min/kg respectively. This means that the body and the kidneys eliminated the drug at these respective rates.
• Endometrial concentrations observed on day 4 and day 7 were 5.02 +/- 3.3 and 12.75 +/- 1.6 micrograms per gram respectively, showing an accumulation of the drug over the course of treatment.
• It was calculated that a steady dosage of 5 mg per kg every 8 hours should achieve average serum Gentamicin concentrations at steady state of 6.47 +/- 1.51, a maximum concentration of 12.74 +/- 1.60, and a minimum concentration of 1.43 +/- 0.57. These results help in understanding the dosing practices required to maintain therapeutic drug levels.
• While it was observed that renal function remained within the base-line range during 7 days of Gentamicin administration, serum urea nitrogen, serum creatinine, and fractional clearance of sodium sulfanilate were measured before and after Gentamicin treatment to monitor the drug’s possible effects on renal function.