The effect of blood sampling site and physicochemical characteristics of drugs on bioavailability after nasal administration in the sheep model.

PURPOSE: Investigate the effect of blood sampling site and physicochemical characteristics of drugs on the pharmacokinetic (PK) parameters obtained after intravenous and nasal administration in sheep and compare results with computer simulations.
METHODS: Three drugs, insulin, morphine, and nicotine, were administered nasally and by intravenous (IV) injection to sheep, and serial blood samples collected concurrently from the carotid artery (insulin, morphine) or cephalic vein (nicotine) and jugular vein. Plasma drug concentrations were measured, and pharmacokinetic and statistical analyses performed, to evaluate sampling site differences.
RESULTS: After nasal insulin, bioavailabilities calculated from the two blood sampling site data were comparable. In contrast, apparent bioavailabilities following nasal morphine or nicotine were significantly higher when sampling was from the jugular vein. These results were supported by computer simulations. These observations are attributed to the greater effects of noninstantaneous mixing of drugs for jugular vein sampling following nasal dosing, compared to the other sampling sites, which is significant for drugs that are rapidly and well absorbed and that have a high volume of distribution (Vd).
CONCLUSION: The results clearly show that the characteristics of the drug and the blood sampling site can have a significant effect on the pharmacokinetic results obtained after nasal administration in sheep.