Plasma pharmacokinetics of ranitidine HCl in foals.

This research investigates how the drug ranitidine HCl is processed over time in the bodies of young foals, after being administered both intravenously (i.v.) and orally (p.o.). The team uses high performance liquid chromatography to measure the concentration of the drug in the plasma over time, allowing them to calculate key pharmacokinetic parameters.

Research Methodology

• This study was carried out on six healthy foals, aged between twelve and sixteen weeks.
• The foals were administered a dose of ranitidine HCl – 2.2 mg/kg intravenously and 4.4 mg/kg orally.
• To monitor the drug concentration in the bloodstream, the team used normal phase high performance liquid chromatography. This technique allows scientists to differentiate and quantify compounds in a mixture.

Results after Intravenous Administration

• The researchers found that the initial concentration of ranitidine HCl in the plasma, 5 minutes post-administration, was a mean of 3266 ng/mL. This concentration decreased to 11 ng/mL 720 minutes after administration.
• The rate of this decline varied among the foals. In two cases, the concentration-time graph was best described by a two-exponent equation. For the remaining four, a three-exponent equation gave the most accurate fit.
• From these data, the team calculated mean pharmacokinetic values including: the apparent volume of distribution (Vdss), the area under the curve (AUC), area under the moment curve (AUMC), mean residence time (MRT) and the clearance rate (Cl). These measures help describe how the drug moves and changes in the body over time.

Results after Oral Administration

• After oral administration, the rate of decline best fitted a two-exponent equation in five out of the six foals. For the remaining foal, a three exponent equation was more suitable.
• Key pharmacokinetic parameters were calculated from these observed data including: the area under the curve (AUC), area under the moment curve (AUMC), mean absorption time (MAT), time to maximum plasma concentration (Tmax), the maximum observed plasma concentration (Cmax), and bioavailability (F). This helps understand how the concentration of drug changes over time when given orally and how much of the administered dose is readily available for action in the body.