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Home / Equine Research Bank / Animals (Basel) / Analgesic and Gastrointestinal Effects of Methadone in Horse...
Animals : an open access journal from MDPI2025; 15(16); 2358; doi: 10.3390/ani15162358

Analgesic and Gastrointestinal Effects of Methadone in Horses Undergoing Orchiectomy.

Abstract: A multimodal approach is recommended to optimize perioperative pain control in animals, although opioid use in horses remains limited due to the risks of central nervous system (CNS) stimulation and reduced intestinal motility. A group of 19 healthy, male, mixed-breed horses were divided into two groups and medicated with acepromazine (0.05 mg kg) and detomidine (10 µg kg), with methadone (0.05 mg kg) (ADM) or saline (ADS) administered intravenously (IV). Physiological variables, intestinal motility, gastric distention, and facial pain (EQUUS-FAP) were evaluated one day before (DB), before the surgical procedure (BS), and at 1, 2, 4, 6, and 8 h (T1h-T8h) after administration (ADM-ADS). Results are presented as means with standard deviation or medians with an interquartile range. Analysis of variance, the Mann-Whitney, and Durbin tests were applied ( < 0.05). Intestinal motility was reduced at T1h and T2h, returning to baseline by T6h and T8h in both groups. Ultrasonographic examination revealed reduced motility, with less significant changes in the left ventral colon (LVC), right ventral colon (RVC), and cecum. Gastric dilatation was more pronounced in the ADM group at T1, 4, 6, and 8h. EQUUS-FAP scores were significantly lower in ADM at T2, 4, and 6h. ADM protocol may aid chemical restraint and analgesia without increasing hypomotility.
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Publication Date: 2025-08-11 PubMed ID: 40867687PubMed Central: PMC12382629DOI: 10.3390/ani15162358Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated the effects of methadone, combined with sedatives acepromazine and detomidine, on pain relief and gastrointestinal function in horses undergoing castration surgery.
  • The research focused on balancing effective perioperative analgesia with the risk of adverse effects such as slowed intestinal motility and CNS stimulation.

Purpose of the Study

  • To evaluate the analgesic (pain-relieving) efficacy of methadone when used in combination with acepromazine and detomidine during horse orchiectomy (castration).
  • To assess the impact of this drug combination on gastrointestinal parameters, specifically intestinal motility and gastric distention, which are crucial for horse health post-surgery.
  • To determine if methadone can provide effective pain management without significantly increasing the risk of gastrointestinal hypomotility or CNS side effects in horses.

Study Design and Methods

  • Nineteen healthy, male, mixed-breed horses were selected for the experiment.
  • The horses were divided into two groups:
    • ADM Group: Received acepromazine (0.05 mg/kg), detomidine (10 µg/kg), and methadone (0.05 mg/kg) intravenously.
    • ADS Group: Received acepromazine, detomidine, and a saline placebo (no methadone) intravenously.
  • Evaluations were carried out at multiple timepoints:
    • One day before the procedure (DB – Baseline)
    • Before surgery (BS)
    • 1, 2, 4, 6, and 8 hours post administration of drugs (T1h to T8h)
  • Monitored variables:
    • Physiological variables (likely heart rate, respiratory rate, etc.)
    • Intestinal motility, via ultrasonographic assessment of several parts of the large intestine (left ventral colon, right ventral colon, and cecum)
    • Gastric distention (measuring potential gas accumulation in the stomach)
    • Facial pain assessment using the EQUUS-FAP scale (a validated equine pain assessment tool)
  • Statistical analyses were conducted using ANOVA, Mann-Whitney, and Durbin tests with a significance threshold of p < 0.05 to identify meaningful differences.

Key Findings

  • Intestinal motility:
    • Both groups exhibited reduced intestinal motility at 1 and 2 hours post administration.
    • Motility returned to baseline by 6 and 8 hours post administration in both groups, indicating temporary effects.
    • The degree of motility reduction was less pronounced in certain areas (left ventral colon, right ventral colon, and cecum), suggesting some regional variation.
  • Gastric distention:
    • The ADM group (with methadone) showed more pronounced gastric distention at 1, 4, 6, and 8 hours compared with the saline group.
    • This indicates a possible increased risk of gastric dilation with methadone usage, though the clinical significance needs careful interpretation.
  • Pain relief:
    • EQUUS-FAP scores were significantly lower in the ADM group at 2, 4, and 6 hours, demonstrating better analgesic effects with methadone.
    • This confirms that adding methadone improved postoperative pain control.

Conclusions and Clinical Implications

  • The combination of acepromazine, detomidine, and methadone (ADM protocol) offered effective chemical restraint and improved analgesia in horses undergoing orchiectomy.
  • Although intestinal motility was transiently reduced in both groups, methadone did not result in significant or prolonged gastrointestinal hypomotility compared to controls.
  • Some increase in gastric distention was observed with methadone, but the overall gastrointestinal safety profile remains acceptable.
  • Use of methadone in this multimodal analgesia protocol may thus be a beneficial option to optimize perioperative pain management in horses without greatly increasing the risk of adverse gastrointestinal effects.

Study Limitations and Future Directions

  • The study had a relatively small sample size (19 horses), which may limit the generalizability of findings.
  • Longer-term effects beyond 8 hours post administration were not investigated.
  • Further research could explore different dosages, combinations, and additional monitoring of CNS side effects to optimize safety and efficacy.
  • Understanding the balance between analgesia and gastrointestinal side effects remains critical for wider opioid use in equine clinical practice.

Cite This Article

APA
Maldonado Moreno N, Alves Moreira J, Araujo De Oliveira L, Sanches Gontijo A, Castilho Baldi ML, Rocha Wenceslau R, Beier SL. (2025). Analgesic and Gastrointestinal Effects of Methadone in Horses Undergoing Orchiectomy. Animals (Basel), 15(16), 2358. https://doi.org/10.3390/ani15162358

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 16
PII: 2358

Researcher Affiliations

Maldonado Moreno, Natalya
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Alves Moreira, Júlia
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Araujo De Oliveira, Luiza
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Sanches Gontijo, Amaranta
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Castilho Baldi, Maria Luiza
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Rocha Wenceslau, Raphael
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.
Beier, Suzane Lilian
  • Department of Clinical and Veterinary Surgery, Veterinary School, Universidade Federal de Minas Gerais, UFMG, Belo Horizonte 31270-901, MG, Brazil.

Grant Funding

  • Fundação de Apoio ao Ensino Pesquisa e Extensão

Conflict of Interest Statement

The authors declare no conflicts of interest.

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Citations

This article has been cited 1 times.
  1. Maldonado Moreno N, Alves Moreira J, Araujo De Oliveira L, Sanches Gontijo A, Castilho Baldi ML, Rocha Wenceslau R, Batista da Silveira Xavier A, Colmenares Guzmán JF, Beier SL. Correction: Maldonado Moreno et al. Analgesic and Gastrointestinal Effects of Methadone in Horses Undergoing Orchiectomy. Animals 2025, 15, 2358. Animals (Basel) 2025 Nov 10;15(22).
    doi: 10.3390/ani15223252pubmed: 41302066google scholar: lookup
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