Pharmacokinetics and selected pharmacodynamic effects of tramadol following intravenous administration to the horse

Toxicokinetics of U-47700, tramadol, and their main metabolites in pigs following intravenous administration: is a multiple species allometric scaling approach useful for the extrapolation of toxicokinetic parameters to humans?

New synthetic opioids (NSOs) pose a public health concern since their emergence on the illicit drug market and are gaining increasing importance in forensic toxicology. Like many other new psychoactive substances, NSOs are consumed without any preclinical safety data or any knowledge on toxicokinetic (TK) data. Due to ethical reasons, controlled human TK studies cannot be performed for the assessment of these relevant data. As an alternative animal experimental approach, six pigs per drug received a single intravenous dose of 100 µg/kg body weight (BW) of U-47700 or 1000 µg/kg BW of tramadol to evaluate whether this species is suitable to assess the TK of NSOs. The drugs were determined in serum and whole blood using a fully validated method based on solid-phase extraction and LC–MS/MS. The concentration–time profiles and a population (pop) TK analysis revealed that a three-compartment model best described the TK data of both opioids. Central volumes of distribution were 0.94 L/kg for U-47700 and 1.25 L/kg for tramadol and central (metabolic) clearances were estimated at 1.57 L/h/kg and 1.85 L/h/kg for U-47700 and tramadol, respectively. The final popTK model parameters for pigs were upscaled via allometric scaling techniques. In comparison to published human data, concentration–time profiles for tramadol could successfully be predicted with single species allometric scaling. Furthermore, possible profiles for U-47700 in humans were simulated. The findings of this study indicate that unlike a multiple species scaling approach, pigs in conjunction with TK modeling are a suitable tool for the assessment of TK data of NSOs and the prediction of human TK data.

Pharmacokinetic properties of tramadol and M1 metabolite in Northeast Brazilian donkeys (Equus asinus)

There is currently little information available on the pharmacokinetics and pharmacodynamics of the analgesic opioid tramadol when used in the veterinary medicine of domestic species. In this study, we aimed to determine the pharmacokinetics of tramadol and its active metabolite M1 following intravenous administration of 2 (T2) and 4 (T4) mg/kg to Northeast Brazilian donkeys. Tramadol and M1 plasma levels were quantified using a validated liquid chromatography-tandem mass spectrometry method. We found that plasma levels of tramadol and M1 were higher than those reported as clinically meaningful in humans for at least 3 hr. However, the pharmacokinetic parameter calculation corrected by dose analysis identified no proportional increase with dose for the AUC of tramadol (T2: 2,663 ± 1,827 vs. T4: 2,964 ± 1,038 ng*h/ml) and M1 (T2: 378 ± 237 vs. T4: 345 ± 142 ng*h/ml). This finding appears to be attributable to a significant increase in clearance and a reduction in the terminal half-life of tramadol. The frequency of adverse effects observed at the higher dose indicates that 2 mg/kg administered intravenously would be suitable for donkeys. Clinical studies are required to determine the implications of these observations regarding the pharmacodynamic response to tramadol in Northeast Brazilian donkeys.

Effects of Orally Administered Resveratrol on TNF, IL-1β, Leukocyte Phagocytic Activity and Oxidative Burst Function in Horses: A Prospective, Randomized, Double-Blinded, Placebo-Controlled Study

Resveratrol, a phytophenol, is a commonly used equine nutraceutical supplement touted to exert anti-inflammatory effects. The effect of orally administered resveratrol on tumor necrosis factor (TNF), interleukin-1β (IL-1β), leukocyte phagocytic activity or oxidative burst function have not been reported in horses. The objective of this study was to determine the effects of a commercially available, orally administered resveratrol product on innate immune functions in healthy adult horses. Whole blood was collected from 12 horses prior to and following 3 weeks of treatment with either the manufacturer’s recommended dose of resveratrol or placebo. Phagocytosis, oxidative burst and pathogen associated molecular pattern (PAMP) motif-stimulated leukocyte production of TNF and IL-1β were compared pre- and post-treatment between treatment groups. Phagocytosis and oxidative burst capacity were evaluated via flow cytometry. Tumor necrosis factor and IL-1β were measured using cytotoxicity and ELISA assays, respectively. There were no significant differences in phagocytosis, oxidative burst or stimulated TNF or IL-1β production between resveratrol and placebo treatment groups. Orally administered resveratrol at a routinely recommended dose for a duration of 3 weeks did not significantly affect phagocytic activity, oxidative burst function or PAMP-stimulated leukocyte cytokine production.

Evaluation of pharmacokinetic properties of vitacoxib in fasted and fed horses

The pharmacokinetic properties of vitacoxib have not been established completely; current dosage recommendations are based on clinical experiences. The primary objective of this study was to describe plasma concentrations and characterize the pharmacokinetics of vitacoxib formulation following oral administrations in horses. Also, the effect of the state of stomach contents on the absorption of vitacoxib was investigated in fed/fasted horses. Blood samples were collected prior to and at various times up to 72 hr post-administration. Drug concentrations were measured using ultra high-performance liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated using Non-Compartmental Analysis Model 200 in WinNonlin™ software. No complications resulting from the vitacoxib administration were noted. All procedures were tolerated well by the horses throughout the study. C_max was 17.5 ± 9.36 ng/ml (fasted) and 9.47 ± 3.53 ng/ml (fed) following oral administrations. AUC_last was 173.7 ± 137.9 ng hr/ml (fasted) and 113.2 ± 70.8 ng h/ml (fed). No significant differences in pharmacokinetic parameters were noted and the results from the pharmacokinetic analysis were similar between the studies, regardless of precision of dosage and fasted and fed conditions. The study extends previous studies describing the pharmacokinetics of vitacoxib following p.o. administration to the horses. Further studies investigating the pharmacokinetics/pharmacodynamics of vitacoxib are necessary to establish adequate therapeutic protocols (optimal dosage and frequency of administration) in horses.

Comparison of Analgesic Effects of a Constant Rate Infusion of Both Tramadol and Acetaminophen Versus those of Infusions of Each Individual Drug in Horses

The choice of analgesic agents for the horse is limited, and many have side effects that can restrict their use for chronic and prolonged pain. Little information has been published on tramadol and acetaminophen use in the horse. The study evaluated the analgesic effects of coadministration of tramadol and acetaminophen compared to those of each drug individually in a crossover study. The study was performed on six healthy horses each infused with the following over 1 hour: control (normal saline), tramadol, acetaminophen, or both (acetaminophen and tramadol infused together). Nociception (using a pressure algometer) and any adverse effects were evaluated before the infusion, at 0, 10, 20, 30, 40, and 50 minutes during the infusion and at 15, 30, and 60 minutes after infusion completion. The pressure algometer was placed on the palmar surface of both the forelimbs. There was no difference in response to nociception between the control and single-agent (acetaminophen or tramadol) groups. However, coadministration of tramadol and acetaminophen resulted in a significant analgesic effect from 20 minutes after starting the infusion until the infusion was completed. Fifteen minutes after discontinuing the infusion, no significant differences remained between the groups. No side effects were seen, with the exception of one horse in the coadministration group which showed paroxysmal ventricular tachycardia 30 minutes after constant rate infusion (CRI) which resolved completely after discontinuing the infusion. Simultaneous infusion of tramadol and acetaminophen resulted in significant analgesia. Further research is required to evaluate its effect and possible side effects in clinical cases, such as horses suffering from laminitis.

Physiological and analgesic effects of continuous-rate infusion of morphine, butorphanol, tramadol or methadone in horses with lipopolysaccharide (LPS)-induced carpal synovitis

BACKGROUND

Continuous-rate infusion (CRI) of drugs results in more stable plasma drug concentrations than administration of intermittent boluses, thus providing greater stability of physiological parameters. The aim of this study was to evaluate the physiologic and analgesic effects of the administration of morphine, butorphanol, tramadol or methadone by CRI in horses with induced synovitis of the radiocarpal joint.

RESULTS

Increased values of cardiorespiratory parameters and body temperature were observed in all groups after initiation of opioid administration, and these increases were sustained throughout the CRI period. Morphine, butorphanol and methadone each caused a reduction in gut sounds, and this effect was greatest in animals that received morphine. Administration of morphine or methadone reduced the degree of lameness after the end of intravenous infusion. Administration of tramadol did not alter the degree of lameness in the animals.

CONCLUSIONS

CRI of morphine or methadone, but not butorphanol or tramadol, provided analgesia in horses with carpal synovitis. All of these opioids increased cardiovascular and respiratory parameters and reduced gut sounds during CRI.

Pharmacokinetics and physiological effects of repeated oral administrations of tramadol in horses

This study evaluated the pharmacokinetics and physiological effects of tramadol during repeated oral administrations in horses. Nine adult healthy horses were administered tramadol at 5 and 10 mg/kg orally every 12 h for 5 days in a randomized, crossover design with a 3-week washout between treatments. Plasma concentrations of tramadol, O- and N-desmethyltramadol (M1 and M2) were measured using Liquid-Chromatography-Mass Spectrometry at predetermined time points following each tramadol administration. Cardiovascular, respiratory and gastrointestinal physiological variables were monitored and adverse events were recorded. Data were analysed with two-way repeated measures anova or Kruskal-Wallis one-way anova on ranks with P < 0.05 considered statistically significant. There were no significant effects of tramadol on the physiological variables. One horse receiving 10 mg/kg tramadol developed mild colic. Following tramadol at 5 and 10 mg/kg, respectively, maximum plasma concentrations (Cmax ) of tramadol ranged from 82-587 and 127-1280 ng/mL, nonconjugated M1 ranged from 2.51-26.7 and 4.88-34.3 ng/mL, and nonconjugated M2 from 12.5-356 and 35.4-486 ng/mL. Corresponding minimum plasma concentrations (Cmin ) of tramadol at 12 h following each dose ranged from 0.8-24 and 3-117 ng/mL. Tramadol accumulated considerably over time, more markedly when given at 10 mg/kg than at 5 mg/kg (accumulation indexes of 3.51 and 1.73 respectively). There was no accumulation of M1 but substantial accumulation of M2. In conclusion, there was accumulation and increase in exposure to tramadol and M2, but not M1, during repeated oral administrations in horses.