Comparison of the cardio‐respiratory effects of methadone and morphine in conscious dogs^††

Abstract

The effects of methadone and morphine were compared in conscious dogs. Six animals received morphine sulfate (1 mg/kg) or methadone hydrochloride (0.5 mg/kg [MET0.5] or 1.0 mg/kg [MET1.0]) intravenously (i.v.) in a randomized complete block design. Cardiopulmonary variables were recorded before (baseline), and for 120 min after drug administration. One outlier was not included in the statistical analysis for hemodynamic data. Morphine decreased heart rate (HR) compared to baseline from 30 to 120 min (-15% to -26%), while cardiac index (CI) was reduced only at 120 min (-19%). Greater and more prolonged reductions in HR (-32% to -46%) and in CI (-24% to -52%) were observed after MET1.0, while intermediate reductions were recorded after MET0.5 (-19 to -28% for HR and -17% to -27% for CI). The systemic vascular resistance index (SVRI) was increased after methadone; MET1.0 produced higher SVRI values than MET0.5 (maximum increases: 57% and 165% for MET0.5 and MET1.0, respectively). Compared to morphine, oxygen partial pressure (PaO(2)) was lower (-12% to -13%) at 5 min of methadone (0.5 and 1.0 mg/kg), while carbon dioxide partial pressure (PaCO(2)) did not change significantly. It was concluded that methadone induces cardiovascular changes that are dose-related and is a more potent cardiovascular depressant agent than morphine in conscious dogs.

Pre-emptive methadone or tramadol analgesia for mastectomy and ovariohysterectomy in bitches

“…However, these parameters are considered to be within the expected ranges and are in agreement with Pereira et al (2013) and Cardozo et al (2014). The cardiovascular effects of methadone are attributed to elevated blood argininevasopressin levels that increase peripheral vascular resistance and, consequently, MAP elevation and reflexive HR decrease (Hellebrekers et al, 1989;Maiante et al, 2008). Nevertheless, the lack of a significant difference in HR between groups after surgical manipulation (20 min) can be explained by the incomplete block of noxious stimuli, which enables the release of catecholamine (Desborough, 2005;Leibetseder et al, 2006).…”

Cardiorespiratory and electrocardiographic effects of methadone or morphine in the perioperative period in anesthetized dogs with continuous rate infusion of propofol and submitted to ovariohysterectomy

“…In dogs, transient apnea is common after anesthetic induction with propofol and, similarly, f may be reduced to 70%, using continuous IV infusion at a dose of 0.8 mg kg -1 min -1 (FERRO et al, 2005). In conscious dogs, Maiante et al (2008) did not observe severe respiratory depression after the application of IV morphine or methadone (0.5 mg kg -1 ). However, this effect becomes important when these agents are administered in combination with other depressant drugs of the respiratory system (CARDOSO et al, 2014), especially general anesthetics (WAGNER, 2002).…”

“…However, methadone also has affinity for N-methyl-D-aspartate (NMDA) and alpha-2 adrenergic receptors, the latter having cardiopulmonary properties including a reduction in HR, which justifies the values found when compared to morphine (FANTONI; CORTOPASSI, 2002). Maiante et al (2008) reported a cardiodepressant effect of methadone when comparing the cardiorespiratory effects of morphine in conscious dogs, by observing HR reductions of 28% and 48% from baseline values at doses of 0.5 mg kg -1 and 1 mg kg -1 of methadone, respectively. Pereira et al (2013) also observed bradycardia after the application of 0.3 mg kg -1 IV methadone, as well as atrioventricular block in dogs undergoing ovariohysterectomy.…”

Refluxo gastroesofágico em cadelas durante ovário-histerectomia convencional submetidas a diferentes medicações pré-anestésicas

“…A dose da acepromazina foi menor quando utilizada em combinação com a metadona do que quando combinada aos outros analgésicos, em razão do maior efeito sedativo dela (Maiante et al, 2009), bem como da proposta de mimetizar as doses utilizadas na rotina hospitalar. Valverde et al (1989) demonstraram que administrar a acepromazina 15 minutos antes do opioide reduz a incidência de vômitos induzidos por essas substâncias, porém essa não é uma prática do meio veterinário e deve ser considerada como manobra a ser incorporada na rotina anestésica.…”

“…Paolozzi et al (2011) observaram elevada incidência (50%) de êmese nas cadelas que receberam 4mg.kg -1 de tramadol, porém essas o receberam por via intravenosa. A metadona apresenta vantagem em relação aos outros opioides, como morfina e hidromorfona, por não provocar êmese em cães (Valverde et al, 1989;Maiante et al, 2009). …”