Pharmacokinetics of a Long-lasting, Highly Concentrated Buprenorphine Solution after Subcutaneous Administration in Rhesus Macaques (Macaca mulatta).

Opioids are essential for use in rhesus macaques (Macaca mulatta) that require multimodal analgesia or those unable to receive NSAID as part of their pain management plan. The current opioid epidemic has universally limited the availability of these vital analgesics, compelling clinicians to investigate other options including novel opioid formulations. A commercially available injectable, long-lasting, highly concentrated buprenorphine solution (HCBS) provides therapeutic plasma concentrations lasting 24 h after a single dose in cats ( Felis catus). We hypothesized that this same HCBS would achieve therapeutic concentrations (≥0.1 ng/mL) for at least 24 h in rhesus macaques. In the current study, 6 healthy, adult rhesus macaques were included in a randomized, 2-period, 2-treatment crossover study. The low dose (0.24 mg/kg SC) achieved a peak plasma concentration of 19.1 ± 5.68 ng/mL at 0.308 ± 0.077 h, with an AUC of 236.4 ± 22.5 h/ng/mL and terminal elimination half-life of 19.6 ± 4.02 h; for the high dose (0.72 mg/kg SC), these parameters were 65.2 ± 14.7 ng/mL, 0.034 ± 0.004 h, 641.3 ± 79.4 h/ng/mL, and 20.6 ± 2.30 h, respectively. The mean plasma concentrations for the low and high doses in rhesus macaques significantly exceeded the therapeutic threshold for 48 and 72 h, respectively. One macaque showed mild somnolence at both doses, and another showed mild pruritus at both doses. These findings show that subcutaneous administration of HCBS provides prolonged and long-lasting therapeutic plasma levels for 48 to 72 h dosing without problematic adverse effects and thus represents a potential new analgesic alternative.