Plasma levels of a methadone constant rate infusion and their corresponding effects on thermal and mechanical nociceptive thresholds in dogs

Background

The present study aimed to collect pharmacokinetic data of a methadone continuous rate infusion (CRI) and to investigate its effect on mechanical and thermal nociceptive thresholds. Seven, 47 to 54 months old beagle dogs, weighing 9.8 to 21.2 kg, were used in this experimental, randomized, blinded, placebo-controlled crossover study. Each dog was treated twice with either a methadone bolus of 0.2 mg kg^− 1 followed by a 0.1 mg kg^− 1 h^− 1 methadone CRI (group M) or an equivalent volume of isotonic saline solution (group P) for 72 h. Mechanical and thermal thresholds, as well as vital parameters and sedation were measured during CRI and for further 24 h. Blood samples for methadone plasma concentrations were collected during this 96 h period.

Results

Percentage thermal excursion (%TE) increased significantly from baseline (BL) until 3 h after discontinuation of CRI in M. Within P and between treatment groups differences were not significant. Mechanical threshold (MT) increased in M until 2 h after CRI discontinuation. Bradycardia and hypothermia occurred in M during drug administration and dogs were mildly sedated for the first 47 h. Decreased food intake and regurgitation were observed in M in five and four dogs, respectively. For methadone a volume of distribution of 10.26 l kg^− 1 and a terminal half-life of 2.4 h were detected and a clearance of 51.44 ml kg^− 1 min^− 1 was calculated. Effective methadone plasma concentrations for thermal and mechanical antinociception were above 17 ng ml^− 1.

Conclusion

A methadone CRI of 0.1 mg kg^− 1 h^− 1 for 3 days after a loading dose results in steady anti-nociceptive effects in an acute pain model in healthy dogs. Main side effects were related to gastrointestinal tract, hypothermia, bradycardia and sedation.

Klinische Anwendbarkeit und Praktikabilität von Alfaxalon zur Kurzanästhesie bei der Katze nach Prämedikation mit Buprenorphin

Ziel dieser Studie war, Praktikabilität und Anwendbarkeit des Injektionsanästhetikums Alfaxalon bei gesunden und erkrankten Katzen zu evaluieren. Im Vordergrund standen Einleitungs-und Aufwachqualität, kardiopulmonale Wirkungen und mögliche Veränderungen bei hämatologischen und blutchemischen Parametern. Material und Methode: Bei 20 felinen Patienten, vorgestellt zu kurzen diagnostischenoder chirurgischen Eingriffen (ASA 1–4), erfolgte eine Anästhesie mit Alfaxalon. Während der Narkose wurden Herz-und Atemfrequenz, endexspiratorischer Kohlendioxidpartialdruck, arterielle Sauerstoffsättigung, mittlerer arterieller Blutdruck und Körperinnentemperatur alle 10 Minuten gemessen und protokolliert. Vor, unmittelbar nach sowie 6 Stunden nach der Anästhesie wurden Blutproben entnommen und hämatologisch sowie blutchemisch untersucht. Die Aufwachphase wurde überwacht und nach einem numerischen Score beurteilt. Ergebnisse: Die Narkoseeinleitung verlief bei allen Patienten ruhig und koordiniert. Die Spontanatmung blieb bei allen Katzen erhalten. Kardiopulmonale Parameter zeigten während der Anästhesie zumeist keine relevanten Veränderungen. Auffällig war eine initial hohe Herzfrequenz (im Durchschnitt > 190/min) nach Narkoseeinleitung, die in den ersten 10 Minuten im Mittel erhöht blieb. Statistisch signifikante Veränderungen (p < 0,05) ergaben sich bei einigen hämatologischen und blutchemischen Parametern sowie dem venösen Säure-Basen-Status, waren jedoch klinisch wenig relevant. Die zwischen 21 und 93 Minuten dauernde Aufwachphase verlief bei den meisten Tieren ruhig. Einige Katzen wiesen milde Anzeichen einer Übererregbarkeit mit Muskelzittern, kurzzeitigem Opisthotonus und Hyperakusis auf. Schlussfolgerung und klinische Relevanz: Alfaxalon eignet sich als Injektionsanästhetikum für Katzen bei kurzen Eingriffen und Behandlungen. Durch seine geringen kardiovaskulären und atemdepressiven Eigenschaften wird es auch von Risikopatienten (ASA 3 und 4) gut toleriert.

[Clinical usability and practicability of Alfaxalone for short-term anaesthesia in the cat after premedication with Buprenorphine]

Objective of this clinical study was to assess the anaesthetic quality (induction and recovery) and utility of short term alfaxalone anaesthesia in healthy and diseased cats. Cardiopulmonary effects and the influence on haematological and biochemical blood parameters were evaluated.

MATERIAL AND METHODS

Twenty feline patients (ASA1-4) were anaesthetized with alfaxalone for various short surgical or diagnostic procedures. Heart rate, breathing rate, end-tidal CO2 partial pressure, arterial oxygen saturation, mean arterial blood pressure and the body temperature were measured and recorded every 10 minutes. Before, after and 6 hours after anaesthesia venous blood samples were taken and haematologic and blood chemistry parameters were determined. Recovery time and quality were assessed by a numerical rating scale.

RESULTS

Anaesthetic induction was rapid and smooth in all cats. Spontaneous respiration was maintained in all cats. Cardiopulmonary parameters mostly remained within a clinically tolerable range. Noticeable was a high heart rate (mean >190 bpm) at the beginning of anaesthesia lasting up to 10 minutes. Statistically significant changes (p<0.05) occurred in some haematologic parameters (RBC, haemoglobin, haematocrit and MCV decreased), electrolytes and venous acid-base-status (bicarbonate, chloride and base excess increased, sodium and potassium decreased) and blood chemistry parameters (alanine aminotransferase, glutamate dehydrogenase and creatinine decreased). None of these changes appeared to have clinical relevance. Recovery was smooth in the majority of cats. Mild signs of hyperexcitability (muscle tremor, short term opisthotonus and hyperacusis) occurred in individual animals. The duration of recovery varied between 21 and 93 minutes.

CONCLUSION AND CLINICAL RELEVANCE

Alfaxalone by repeated intravenous injection is suitable for short-term diagnostic and surgical procedures in cats. Because of its minor cardiovascular effects and slight respiratory depression, it is also well tolerated by patients with increased anaesthetic risk (ASA 3 and 4).

Intraoperative use of a reflective blanket (Sirius rescue sheet) for temperature management in dogs less than 10 kg

OBJECTIVES

To compare the effects of the Sirius rescue sheet with gel pads versus gel pads alone on intraoperative body temperature in dogs less than 10 kg.

METHODS

Forty small breed dogs undergoing elective surgical procedures were randomly assigned to two groups. One group was intraoperatively laid on warmed gel pads, and the other group was additionally wrapped in a Sirius rescue sheet. Oesophageal body temperature was determined every 10 minutes and compared between groups. Temperature of gel pads was measured preoperatively and postoperatively to compare heat loss of the gel pads between groups.

RESULTS

The body temperature of dogs wrapped with the Sirius rescue sheet increased intraoperatively. In dogs just lying on warmed gel pads, a decrease in mean body temperature was revealed and mean body temperatures differed between groups after 40 minutes. Extent of heat loss from the gel pads did not differ between the groups.

CLINICAL SIGNIFICANCE

The Sirius rescue sheet, used in addition to warmed gel pads, led to higher intraoperative body temperatures in small breed dogs undergoing surgical procedures to the extremities and the head. The cost-effectiveness and ease of handling make this a useful addition to clinical practice.