Enzymatic degradation of leuprolide in rat intestinal mucosal homogenates.

The purpose of this study was to evaluate in vitro enzymatic degradation and protection of leuprolide acetate in the mucosal homogenates of rat small intestine. When leuprolide was incubated at 37 degrees C with the homogenates, it was degraded quickly. The apparent Michaelis-Menten constant, K(m), and the maximal reaction velocity, Vmax, for leuprolide were 898 mM and 3.4 nmol/min/mg protein, respectively. At least four metabolites of leuprolide were observed in HPLC chromatograms, which were related to cleavages by some serine proteases. In the presence of protease inhibitors in the incubation medium, degradation of leuprolide was significantly suppressed by antipain and 3,4-dichloroisocoumarin (DCI), whereas bestatin and p-hydroxymercuribenzoic acid (PCMB) showed weaker protection than antipain and DCI, and alpha 2-macroglobulin (MG) exhibited no protection. When a w/o/w emulsion formulation was used, rapid degradation of the drug in intestinal homogenates was also inhibited. Therefore, the present study with representative protease inhibitors and a w/o/w formulation revealed that the enzymatic degradation of leuprolide is preventable in the rat intestinal mucosal homogenates.

Permeability and absorption of leuprolide from various intestinal regions in rabbits and rats.

The in vitro permeability and in vivo absorption of leuprolide in different intestinal regions were measured to investigate the feasibility for site-specific delivery of leuprolide in the gastrointestinal (GI) tract. In vitro permeability of leuprolide in the rabbit GI tract was performed using a side-by-side diffusion apparatus and the permeability coefficients in the jejunum, ileum and colon were 0.27x10(-7), 2.96x10(-7) and 7.85x10(-7)cm/s, respectively. Varying the donor drug concentrations from 2 to 10 mg/ml, the permeability coefficients were independent of the donor concentration, suggesting the transport mechanism of passive diffusion. Using an intestine loop model in anesthetized rats, bioavailabilities of leuprolide in the jejunum, ileum and colon were 1.28, 5.62 and 9.59%, respectively. Drug recovery from the loop 5 h after dosing was 10.7% in jejunum, 24.5% in ileum and 40.7% in colon. Additional in vivo studies using conscious rats showed that the bioavailability of leuprolide was less than 1% for both ileal and colonic administration. In vivo absorption of leuprolide from ileum was not significantly different from colon in conscious rats. Sodium salicylate, a permeation enhancer, was co-administered with leuprolide to the rat ascending colon, and results showed a 4-fold increase in the bioavailability in conscious rats. Thus, in vivo studies indicate that both absorption and enzymatic degradation of leuprolide in the GI tract is site-dependent and the lower intestine may be an advantageous region for oral delivery of leuprolide.

Sublingual absorption of leuprolide: comparison between human and animal models.

Leuprolide is a potent luteinizing hormone releasing hormone agonist used for the treatment of hormone-dependent diseases. It is a decapeptide drug currently administered by subcutaneous and intramuscular injection because it is not orally bioavailable. In the present study, sublingual gel formulations of leuprolide were administered to dogs, monkeys and humans. Plasma samples were analyzed by radioimmunoassay. Absorption and pharmacokinetics of leuprolide following sublingual administration were compared and evaluated. It was found that the extent and rate of absorption were similar between humans and monkeys following sublingual dosing of leuprolide formulations. A prolonged absorption of up to approximately 6 h after dosing was observed in both humans and monkeys. The rate and extent of absorption were significantly higher in dogs than in humans. The estimate of absolute bioavailability of leuprolide was 46.7% in dogs compared with 2.7% in monkeys at an equivalent dose of 0.45 mg/kg. Absolute bioavailabilities in humans were 2.0, 2.3 and 2.4% at doses of 1.125, 2.25 and 4.5 mg, respectively. Based on these results, the dog is not an appropriate animal model for evaluating sublingual absorption of leuprolide. This work suggests that monkey is a preferred model for the development and assessment of sublingual formulations of leuprolide.

5-fluorouracil urethral suppositories for the eradication of condyloma accuminata.

The formulation of a 5-fluorouracil urethral suppository is described. The suppositories have been found extremely successful in the eradication of intraurethral condylomas. They have provided better patient compliance and dosage monitoring, and have extended patient usefulness to male and female subjects.