Providing appropriate analgesia is essential in minimizing pain and maintaining optimal animal care and welfare in laboratory animals. Guinea pigs are common animal models in biomedical research, often requiring analgesic support. Here we evaluated the pharmacokinetics and efficacy of a sustained-release formulation of buprenorphine (Bup-SR) in this species. Guinea pigs (n = 7 each group) received either Bup-HCl (0.05 mg/kg BID for 3 d) or Bup-SR (0.3 mg/kg once). Plasma collection and measurement of paw-withdrawal pressure (PWP) was conducted at 0, 1, 3, 6, 12, 26, 48, and 72 h after treatment. Plasma levels of Bup-HCl peaked at 2331 pg/mL at 1 h after administration and declined to 165 pg/mL by 12 h. Plasma concentrations of Bup-SR peaked at 1344 pg/mL at 26 h after administration and declined to 429 pg/mL by 48 h. The PWP of the Bup-HCltreated guinea pigs peaked at 674 g at 1 h and declined to 402 g at 6 h, whereas that of Bup-SRtreated guinea pigs at 1 h was 361 g, 555 g at 6 h (significantly higher than that after Bup-HCl), and peaked at 680 g at 12 h. The PWP of both treatments was similar from 24 to 72 h and ranged from 348 to 450 g. The plasma concentration and PWP showed good correlation. These results suggest that Bup-SR provides consistent analgesia equivalent to that of Bup-HCl for a prolonged period of time and that Bup-SR is an alternative method of analgesia in guinea pigs.