PHARMACOKINETICS OF ALPHA-DIHYDROERGOCRIPTINE IN RATS AFTER SINGLE INTRAVENOUS AND SINGLE AND REPEATED ORAL ADMINISTRATIONS

The pharmacokinetics of alpha-dihydroergocriptine methane sulphonate in rats were investigated using an HPLC method for the detection of unchanged alpha-dihydroergocriptine (DHEK) in plasma, organs (kidneys, heart, lungs, spleen, liver, and brain), and urine. The plasma profile of DHEK obtained after intravenous administration at a dose of 5mg kg(-1) (as base) of DHEK methane sulphonate showed a three compartment pharmacokinetic model with an elimination half-life of 6.78 h. The kinetics of DHEK after a single oral administration at a dose of 20mg kg(-1) (as base) showed two peaks: the second peak, at about 6 h, was probably due to an enterohepatic cycle. The disposition of DHEK consisted of an absorption half-life of 0.02h, a distribution half-life of 2.15h and an elimination half-life of 5.83h. The pharmacokinetics of DHEK, after repeated oral administrations at the same dose, were similar to those after a single oral administration. The absolute bioavailability was 4.14% after a single oral administration and 3.95% after repeated oral administrations. The analysis of the organs showed that DHEK was rapidly absorbed and distributed in all tissues, mostly in lungs, kidneys, and liver, but it is interesting to observe that it also reached the brain. After repeated oral administrations plasma and tissue concentrations were similar to those obtained after a single administration; therefore it is possible to exclude the onset of autoinduction or accumulation phenomena of DHEK in rats' organs. Urinary excretion of the unchanged drug was low (0.38% of the administered dose in the intravenous route and 0.04% in the oral route), being in agreement with a low oral bioavailability and a rapid and extensive metabolism (first-pass effect).