The effects of ketoconazole and cimetidine on the pharmacokinetics of oral tramadol in greyhound dogs

Crizotinib inhibits the metabolism of tramadol by non-competitive suppressing the activities of CYP2D1 and CYP3A2

Objectives

To investigate the interaction between tramadol and representative tyrosine kinase inhibitors, and to study the inhibition mode of drug-interaction.

Methods

Liver microsomal catalyzing assay was developed. Sprague-Dawley rats were administrated tramadol with or without selected tyrosine kinase inhibitors. Samples were prepared and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for analysis. Besides, liver, kidney, and small intestine were collected and morphology was examined by hematoxyline-eosin (H&E) staining. Meanwhile, liver microsomes were prepared and carbon monoxide differential ultraviolet radiation (UV) spectrophotometric quantification was performed.

Results

Among the screened inhibitors, crizotinib takes the highest potency in suppressing the metabolism of tramadol in rat/human liver microsome, following non-competitive inhibitory mechanism. In vivo, when crizotinib was co-administered, the AUC value of tramadol increased compared with the control group. Besides, no obvious pathological changes were observed, including cell morphology, size, arrangement, nuclear morphology with the levels of alanine transaminase (ALT) and aspartate transaminase (AST) increased after multiple administration of crizotinib. Meanwhile, the activities of CYP2D1 and CYP3A2 as well as the total cytochrome P450 abundance were found to be decreased in rat liver of combinational group.

Conclusions

Crizotinib can inhibit the metabolism of tramadol. Therefore, this recipe should be vigilant to prevent adverse reactions.

Dosing protocols to increase the efficacy of butorphanol in dogs

The purpose of this study was to improve butorphanol dosing in dogs. Twelve Beagles (6 males, 6 females) were enrolled. Six were randomly allocated to each butorphanol treatment: IV (0.4 mg/kg), IV loading dose (0.2 mg/kg) with IV CRI (0.2 mg/kg/h for 8 h), SC (0.4 mg/kg), SC (0.8 mg/kg) with an equal volume sodium bicarbonate (SC-bicarbonate), and IV after CYP inhibitors. We hypothesized that the CRI would produce longer durations than IV bolus, and SC-bicarbonate suspension would produce longer durations than SC. Hypothermia, an opioid effect paralleling antinociception in dogs, and sedation were evaluated. Pharmacokinetics and CYP inhibitor effects on butorphanol pharmacokinetics were determined. Rectal temperatures were significantly lower than baseline from 1.5-4 h (IV), 1-5 h (CRI), and 2-7 h (SC-bicarbonate), but not after SC. Dogs in all treatments had sedation. Butorphanol's half-life was ~1.5 h. SC-bicarbonate had lower bioavailability (61%) relative to SC, with no sustained release, and the CRI mean steady-state plasma concentration was 43.1 ng/ml. CYP inhibitors had minor pharmacokinetic effects on butorphanol. Butorphanol 0.4 mg/kg IV and 0.2 mg/kg loading dose with 0.2 mg/kg/h CRI decreased rectal temperature, but 0.4 mg/kg SC did not. Further studies are required to determine clinical analgesia of butorphanol.

Pharmacokinetics and analgesic efficacy of intranasal administration of tramadol in dogs after ovariohysterectomy

OBJECTIVE

To assess analgesic efficacy and the pharmacokinetics of intranasal (IN) tramadol in dogs following ovariohysterectomy.

STUDY DESIGN

Randomized, blinded clinical study.

ANIMALS

A total of 30 bitches undergoing elective ovariohysterectomy.

METHODS

Dogs were randomly assigned to one of three experimental groups (10 dogs per group): IN tramadol 4 mg kg^-1 (group T-IN), intravenous (IV) tramadol 4 mg kg^-1 (group T-IV) and IV methadone 0.2 mg kg^-1 (group M). Drugs were administered at extubation. At established time points (before surgery and up to 8 hours after drug administration) analgesia was assessed using the Italian version of the Glasgow Composite Measure Pain Scale Short Form and physiological variables were recorded. To determine the pharmacokinetics of IN tramadol, blood samples were collected at predetermined time points. Shapiro-Wilk test was used to assess whether data were normally distributed and consequently parametric or non parametric tests were applied. A p value < 0.05 was considered significant.

RESULTS

No significant intergroup differences were observed in the dogs that were administered rescue analgesia and time of its administration. Excluding dogs that were administered rescue analgesia, no significant intergroup differences emerged in pain scores and physiological variables, except for a lower rectal temperature in group M compared with the tramadol groups. After IN administration, tramadol was rapidly absorbed into the systemic circulation, reaching its maximum concentration (range 74.74-200.29 ng mL^-1) within 30-60 minutes, it then decreased rapidly and was detectable in plasma for up to 2 hours after treatment in all dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

IN tramadol administration appears to be as effective as IV tramadol and methadone treatments in pain management of dogs after elective ovariohysterectomy. Given its low concentrations and short detection time in plasma after the IN route, systemic tramadol action appears unlikely.

Oral Coadministration of Fluconazole with Tramadol Markedly Increases Plasma and Urine Concentrations of Tramadol and the O-Desmethyltramadol Metabolite in Healthy Dogs

Tramadol is used frequently in the management of mild to moderate pain conditions in dogs. This use is controversial because multiple reports in treated dogs demonstrate very low plasma concentrations of O-desmethyltramadol (M1), the active metabolite. The objective of this study was to identify a drug that could be coadministered with tramadol to increase plasma M1 concentrations, thereby enhancing analgesic efficacy. In vitro studies were initially conducted to identify a compound that inhibited tramadol metabolism to N-desmethyltramadol (M2) and M1 metabolism to N,O-didesmethyltramadol (M5) without reducing tramadol metabolism to M1. A randomized crossover drug-drug interaction study was then conducted by administering this inhibitor or placebo with tramadol to 12 dogs. Blood and urine samples were collected to measure tramadol, tramadol metabolites, and inhibitor concentrations. After screening 86 compounds, fluconazole was the only drug found to inhibit M2 and M5 formation potently without reducing M1 formation. Four hours after tramadol administration to fluconazole-treated dogs, there were marked statistically significant (P < 0.001; Wilcoxon signed-rank test) increases in plasma tramadol (31-fold higher) and M1 (39-fold higher) concentrations when compared with placebo-treated dogs. Conversely, plasma M2 and M5 concentrations were significantly lower (11-fold and 3-fold, respectively; P < 0.01) in fluconazole-treated dogs. Metabolite concentrations in urine followed a similar pattern. This is the first study to demonstrate a potentially beneficial drug-drug interaction in dogs through enhancing plasma tramadol and M1 concentrations. Future studies are needed to determine whether adding fluconazole can enhance the analgesic efficacy of tramadol in healthy dogs and clinical patients experiencing pain.

Identification of canine cytochrome P-450s (CYPs) metabolizing the tramadol (+)-M1 and (+)-M2 metabolites to the tramadol (+)-M5 metabolite in dog liver microsomes

We previously showed that (+)-tramadol is metabolized in dog liver to (+)-M1 exclusively by CYP2D15 and to (+)-M2 by multiple CYPs, but primarily CYP2B11. However, (+)-M1 and (+)-M2 are further metabolized in dogs to (+)-M5, which is the major metabolite found in dog plasma and urine. In this study, we identified canine CYPs involved in metabolizing (+)-M1 and (+)-M2 using recombinant enzymes, untreated dog liver microsomes (DLMs), inhibitor-treated DLMs, and DLMs from CYP inducer-treated dogs. A canine P-glycoprotein expressing cell line was also used to evaluate whether (+)-tramadol, (+)-M1, (+)-M2, or (+)-M5 are substrates of canine P-glycoprotein, thereby limiting their distribution into the central nervous system. (+)-M5 was largely formed from (+)-M1 by recombinant CYP2C21 with minor contributions from CYP2C41 and CYP2B11. (+)-M5 formation in DLMs from (+)-M1 was potently inhibited by sulfaphenazole (CYP2C inhibitor) and chloramphenicol (CYP2B11 inhibitor) and was greatly increased in DLMs from phenobarbital-treated dogs. (+)-M5 was formed from (+)-M2 predominantly by CYP2D15. (+)-M5 formation from (+)-M1 in DLMs was potently inhibited by quinidine (CYP2D inhibitor) but had only a minor impact from all CYP inducers tested. Intrinsic clearance estimates showed over 50 times higher values for (+)-M5 formation from (+)-M2 compared with (+)-M1 in DLMs. This was largely attributed to the higher enzyme affinity (lower Km) for (+)-M2 compared with (+)-M1 as substrate. (+)-tramadol, (+)-M1, (+)-M2, or (+)-M5 were not p-glycoprotein substrates. This study provides a clearer picture of the role of individual CYPs in the complex metabolism of tramadol in dogs.