Effects of methadone on gastrointestinal transit time and pH of conscious cats

Abstract

Objectives: The aim of the present study was to evaluate the effects of methadone on esophageal, gastric, total intestinal and overall gastrointestinal (GI) transit times and pH in cats. Methods: In a randomized, placebo-controlled crossover study, six female domestic shorthair cats were administered a pH capsule via the oral route immediately after a 1 h feeding regimen. Cats were randomly assigned an order to receive two treatments immediately after administration of the pH capsule. Each treatment consisted of one intramuscular (IM) injection: treatment SAL consisted of one injection of 0.9% saline solution (0.06 ml/kg) and treatment MET consisted of one injection of methadone HCl (0.6 mg/kg). pH was used to determine the location of the capsule within the GI tract. Esophageal, gastric and total GI transit times and intestinal transit time were compared between treatments using the Wilcoxon match-pairs signed rank test and paired two-tailed t-test, respectively. Mean esophageal, gastric and intestinal pH were compared using the Wilcoxon match-pairs signed rank test. Results: There were no significant differences found in esophageal (range 1–96 mins vs 2–144 mins; P = 0.56), gastric (range 907–5473 mins vs 1065–10,414 mins; P = 0.06), intestinal (range 1194–2406 mins vs 928–2541 mins; P = 0.92) and total GI transit times (2,244–6674 mins vs 2191–11,486 mins; P = 0.06) between the SAL and MET treatments. There were no significant differences found in esophageal (range 5.4–6.2 vs 4.1–6.2; P = 0.063), gastric (range 1.3–2.9 vs 1.6–2.9; P >0.99) or intestinal (range 7.1–8.3 vs 6.0–8.3; P = 0.063) pH between the SAL and MET treatments. Conclusions and relevance: A single 0.6 mg/kg dose of IM methadone did not produce changes in the GI transit time or pH when compared with saline. This dose of methadone can be used safely in cats without opioid-induced GI motility effects; however, other adverse effects may still occur.