Lymphatic and portal venous absorption of phenobarbital and thiopental in the dog.

Lymphatic and portal venous absorption of gastrically administered thiopental and phenobarbital were compared in the dog. Thiopental concentrations in lymph were significantly higher than phenobarbital concentrations for 30 min after drug administration. Disparity between portal plasma and lymph concentrations for thiopental during the first 15 min was about 1/3 as great as the same difference for phenobarbital. Thiopental displayed an average of twice the affinity for lipid (chylomicron) lymph as did phenobarbital. Because of its greater lipid solubility, thiopental is absorbed more by lymph than is phenobarbital. Both barbiturates are absorbed more quantitatively by the portal rather than lymphatic circulation, probably due to variation in the rate of flow of these 2 systems.