Nafarelin controlled release injectable: theoretical clinical plasma profiles from multiple dosing and from mixtures of microspheres containing 2 per cent, 4 per cent and 7 per cent nafarelin.

Nafarelin controlled release injectable (CRI) releases a decapeptide drug for target one month therapy. Nafarelin, a luteinizing hormone releasing hormone agonistic analogue, is microencapsulated in biodegradable poly(lactide-co-glycolide) microspheres and given by intramuscular injection. Clinical data from a human single dose Phase I clinical study are modelled to develop theoretical multiple dose profiles and theoretical single dose profiles from mixtures of two or three formulations. Single dose injections of nafarelin CRI microspheres (4 mg nafarelin) containing 2, 4, or 7 per cent nafarelin all achieve useful plasma drug levels throughout the target 30 day interval. Therapeutic suppression of testosterone levels was observed in all subjects participating in the phase I clinical study. Highest plasma nafarelin levels are achieved in the 0-10 and 20-35 day post-injection intervals. Theoretical multiple dosing profiles generated from the single dose clinical results show significant oscillations in plasma nafarelin levels depending on the particular dosing interval selected. Thirty or forty day dosing intervals yield significant variability in plasma nafarelin levels at steady state; 15 day dosing intervals show less variability. Therapeutic testosterone suppression was observed in the single dose study, so the nafarelin dose per injection can be reduced in multiple dosing therapies. Theoretical plasma nafarelin profiles from certain mixtures of 2 and 4 per cent nafarelin microspheres or 2 and 7 per cent nafarelin microspheres indicate that a 60 day product could be achieved. In general, all three formulations yield their lowest plasma drug levels during the 10-20 day post-injection interval. Therefore any mixture of these formulations will likewise exhibit low plasma drug levels during this interval.