Tramadol Metabolism toO-Desmethyl Tramadol (M1) andN-Desmethyl Tramadol (M2) by Dog Liver Microsomes: Species Comparison and Identification of Responsible Canine Cytochrome P450s

Abstract

Tramadol is widely used to manage mild to moderately painful conditions in dogs. However, this use is controversial since clinical efficacy studies in dogs showed conflicting results, while pharmacokinetic studies demonstrated relatively low circulating concentrations of O-desmethyltramadol (M1). Analgesia has been attributed to the opioid effects of M1, while tramadol and the other major metabolite (N-desmethyltramadol, M2) are considered inactive at opioid receptors. The aims of this study were to determine whether cytochrome P450 (CYP) dependent M1 formation by dog liver microsomes is slower compared with cat and human liver microsomes; and identify the CYPs responsible for M1 and M2 formation in canine liver. Since tramadol is used as a racemic mixture of (+)- and (-)-stereoisomers, both (+)-tramadol and (-)- tramadol were evaluated as substrates. M1 formation from tramadol by liver microsomes from dogs was slower than from cats (3.9-fold), but faster than humans (7-fold). However, M2 formation by liver microsomes from dogs was faster than from cats (4.8-fold) and humans (19-fold). Recombinant canine CYP activities indicated that M1 was formed by CYP2D15, while M2 was largely formed by CYP2B11 and CYP3A12. This was confirmed by dog liver microsomes studies that showed selective inhibition of M1 formation by quinidine and M2 formation by chloramphenicol and CYP2B11 antiserum, and induction of M2 formation by phenobarbital. Findings were similar for both (+)-tramadol and (-)-tramadol. In conclusion, low circulating M1 concentrations in dogs is explained in part by low M1 formation and high M2 formation, which are mediated by CYP2D15 and CYP2B11/CYP3A12, respectively.

Effects of tramadol and acepromazine on intraocular pressure and pupil diameter in young healthy cats

“…As a result of impaired glucuronidation in this species, the isoform M1 tends to persist for longer periods in cats than in dogs (CAGNARDI et al, 2011). Additionally, the rate of M1 formation by liver microsomes of cats are 3.9 times faster than that observed in dogs (PEREZ et al, 2016). The significant reduction of PD values observed from the middle time point to the end of our experiment suggested that tramadol is able to sustain mydriasis in cats for at least 2 hours.…”

“…In humans, the pupillary response to tramadol is influenced by the genotype CYP2D6, which encodes isoenzymes that metabolize tramadol to its active metabolite (M1) (MATOUSKOVAet al, 2011). Thus, individuals that do not express such genotype tend to develop mydriasis when treated with tramadol; while the ones that express CYP2D6, miosis was observed (PEREZ et al, 2016). Regarding the pharmacokinetics Figure 1 -Mean values ± standard error of pupil diameter (mm) (A) and intraocular pressure (mmHg) (B) before (baseline) and after 15, 30, 60 and 120 minutes of the intramuscular administration of acepromazine, tramadol and the combination acepromazine and tramadol in young healthy cats.…”

Efeitos adversos da morfina, metadona e tramadol no pós-operatório de cães submetidos à cirurgia da coluna vertebral: 180 casos (2011-2016)

“…O principal metabólito do tramadol reconhecidamente responsável pela analgesia em nível de receptores opioides é o O-desmetiltramadol (M1) (Kukanich & Papich 2004, 2011. A produção deste metabólito em cães é realizada pelo grupo de enzimas hepáticas citocromo P450, subtipo 2D15 a qual sofre polimorfismo individual em cães, fazendo com que a produção deste metabólito apresente uma grande variação individual nessa espécie (Giorgi et al 2010, Perez et al 2016, o que faz com que a concentração circulante do M1 em cães seja menor do que em humanos e gatos o que justifica menor eficiência analgésica (Perez et al 2016), além de explicar também a diferença individual quanto aos efeitos do tramadol em diferentes cães (McMillan et al 2008, Kogel et al 2014, Goudie-Deangelis & Woodhouse 2015, o que provavelmente acontece na prática clínica e refletiu no presente estudo. Embora alguns estudos comprovaram a eficácia analgésica do tramadol no pós-operatório de diferentes tipos de cirurgia (Yazbek & Fantoni 2005, Buhari et al 2012, a sua real aplicação, nas doses aqui estudadas, no pós-operatório de cirurgias que envolvem a coluna vertebral ainda é questionável, necessitando de estudos controlados direcionados à avaliação de dor após esse tipo de procedimento em cães.…”

Identification of the cytochrome P450 enzymes involved in the oxidative metabolism of trantinterol using ultra high-performance liquid chromatography coupled with tandem mass spectrometry

“…Among these methods, HPLC-MS/MS method has been adopted extensively in the recent years due to the highselectivity, high-sensitivity, and high-speed separations, but reference standards of the analyzed metabolites are required for the quantication. [24][25][26][27][28] In our study, reference standards of the two metabolites were synthesized or puried in our laboratory, and the structures were conrmed using nuclear magnetic resonance (NMR) as described previously. 2 The purities of these two metabolites were determined by HPLC method to be above 99.0%.…”