The FDA intends to award a firm-fixed-price, sole-source purchase order to Charles River Laboratories in Mattawan, MI, for a 12-month preclinical in vivo study in male rats. The study will simultaneously measure respiratory and cardiovascular changes caused by polysubstance-induced respiratory depression and evaluate naloxone and alternative reversal agents, with PK blood samples sent to the FDA. Work will occur in four sequential phases using whole body plethysmography, implanted telemetry, IV dosing, and ANOVA analysis under non-GLP conditions in an AAALAC-accredited facility. The period of performance is 12 months, with study initiation anticipated within 2 months of award subject to animal availability. This notice is not a request for competitive proposals.