Metoprolol Exhibits Discrete Pharmacokinetics Using Various Sites of Sample Collection after Single Oral Dose Administration of Metoprolol Tartrate in SD Rats

The aim of the study was to investigate the influences of various routes of sampling on the pharmacokinetics profile metoprolol after single oral dose administration of metoprolol tartrate in rats. For this single dose parallel studies were conducted in SD rats at 5 mg/kg of metoprolol tartrate. In our investigation, significant differences were observed in the plasma PK profile of metoprolol using various routes of sample collection. The mean peak plasma metoprolol concentration obtained from jugular (C max ; 170.0 ng/mL) and saphenous (C max ; 113.2 ng/mL) routes were comparable. Similarly, retro-orbital route C max (50.0 ng/mL) was comparable with C max (76.2 ng/mL) of femoral route. In contrast, the C max (39.3 ng/mL) obtained from tail vein sampling route was significantly different (p ≤ 0.05) from all other sampling sites. The C max obtained from tail vein sampling site was approximately 2–4 folds less compared to other routes of sampling except for retro-orbital sampling site. Corresponding differences were also observed for other PK parameters. It was concluded that the sampling sites have profound impact on the PK parameters of metoprolol after single dose oral administration in rats.