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Serum Concentration and Urinary Excretion of the Luteinizing Hormone-Releasing Hormone Agonist Buserelin in Patients with Endometriosis

Division of Gynecological Endocrinology (L.K., K.B., B.R.), Department of Obstetrics and Gynecology, University of Heidelberg D-6900 Heidelberg, West Germany
Hoechst AG (J.S., G.J.-S., H.T.) D-6230 Frankfurt 80, West Germany

Address all correspondence and requests for reprints to: Dr. L. Kiesel, Universitats-Frauenklinik, Voss-Strasse 9, D-6900 Heidelberg, West Germany.

We studied the pharmacokinetics of iv and intranasally administered buserelin, a LHRH agonist peptide, in 14 women with endometriosis. Serum and urinary buserelin concentrations were determined by specific RIA (buserelin antiserum AS-639). Intact buserelin and the metabolites in urine were separated by reverse phase high performance liquid chromatography and measured by RIA. The mean serum buserelin concentrations were 101 ± 33 (±SD) ng/mL 20 min and 1.12 ± 0.12 ng/mL 360 min after its iv injection in 6 women, and the mean elimination half-life between 20 and 360 min was 51 min. In serum, intact buserelin was the main constituent (10 min, 90%; 120 min, 74%; 360 min, 52%), and the major metabolite was the buserelin-(5–9) pentapeptide (10 min, 0.6%; 120 min, 19%; 360 min, 12%). In the urine collected 0–1 h after buserelin administration, intact buserelin was 66% and the 5–9 pentapeptide was 28% of the total excretion. In the urine collected between 6–24 h after buserelin administration, intact buserelin accounted for 67% and the 5–9 pentapeptide for 32% of the total excretion. The urinary buserelin concentration was 1345 ± 156 µg/g creatinine 1 h and 25 ± 5 µg/g creatinine 6–24 h after buserelin administration. Serum LH, FSH, and estradiol concentrations increased acutely up to 10-fold above basal values; the mean peak LH, FSH, and estradiol values occurred at 180–240 min, 240 min, and 24 h, respectively. In therapeutic studies with buserelin nasal spray in 5 women, serum concentrations of 0.9–1.4 ng/mL were found 15 min after a single dose of 300 ng, intranasally, and the urinary excretion was 2.52–3.68 µg/24 h during daily administration of 3 doses of 300 µg at intervals of 8 h. These results confirm that buserelin is slowly inactivated and remains available to pituitary receptors for a prolonged period after its iv or intranasal administration.

Received June 14, 1988.