J. vet. Pharmacol. Therap. doi: 10.1111/jvp.12133
SHORT COMMUNICATION
Pharmacokinetics of tramadol and its major metabolite after intramuscular administration in piglets C. VULLO* T.-W. KIM
†
M. MELIGRANA* C. MARINI* & M. GIORGI
‡
*School of Biosciences and Veterinary Medicine, University of Camerino, Matelica, Macerata, Italy; †College of Veterinary Medicine, Chungnam National University, Daejeon, South Korea; ‡Department of Veterinary Sciences Via Livornese (lato monte), San Piero a Grado, Pisa, Italy
Vullo, C., Kim, T.-W., Meligrana, M., Marini, C., Giorgi, M. Pharmacokinetics of tramadol and its major metabolite after intramuscular administration in piglets. J. vet. Pharmacol. Therap. doi: 10.1111/jvp.12133. Tramadol (T) is a centrally acting atypical opioid used for treatment of dogs. Piglets might experience pain following castration, tooth clipping and tail docking and experimental procedures. The aim of this study was to assess the pharmacokinetics of T and its active metabolite M1 in male piglets after a single intramuscular injection. Six healthy male piglets were administered T (5 mg/kg) intramuscularly. Blood was sampled at scheduled time intervals and drug plasma concentrations evaluated by a validated HPLC method. T plasma concentration was quantitatively detectable from 0.083 to 8 h. M1 was quantified over a shorter time period (0.083–6 h) with a Tmax at 0.821 h. The study demonstrated that piglets produce a larger amount of M1 compared with dogs, horses and goats. The human minimum effective concentration of M1 (40 ng/mL) was exceeded for over 3 h in piglets. If it is assumed to also apply to piglets, it could be speculated that the drug efficacy might exert its action over 3 h or longer. This assumption has to be confirmed by further specific pharmacokinetic/pharmacodynamic studies. (Paper received 5 January 2014; accepted for publication 23 March 2014) Mario Giorgi, Department of Veterinary Sciences Via Livornese (lato monte), Pisa, 56122 San Piero a Grado, Italy. E-mail: [email protected]
Tramadol (T) is a centrally acting, atypical opioid that has been used clinically for the last three decades to treat pain in humans. T displays a low affinity for the mu- and delta-opioid receptors, and weaker affinity for the kappa-subtype; it also interferes with the neuronal release and re-uptake of serotonin and noradrenaline in descending inhibitory pathways (Raffa et al., 1992). The clinical efficacy of T administration is dependent from its metabolism, because of the different analgesic activities of its metabolites. In fact, O-desmethyl-tramadol hydrochloride (M1), the only active metabolite, is 200 times more affine at the mu-receptor than the parent drug T, accounting for most of the clinical effect (Raffa et al., 1992). The metabolism of this drug has been investigated in different species including rodents (Lintz et al., 1981), ruminants (de Sousa et al., 2008; Giorgi et al., 2010a; Cox et al., 2011), pets (KuKanich & Papich, 2004; Pypendop & Ilkiw, 2008; Giorgi et al., 2009a,b), horses (Giorgi et al., 2006, 2007, 2009c; De Leo et al., 2009) and zoo animals (Souza & Cox, 2011). Similar metabolites are produced in all these species but in different amounts. Despite its long-term use, our understanding and prediction of the time course of its pharmacological effects are still complicated by the presence of active metabolites and the coexistence of opioid and nonopioid mechanisms of action. The clinical effectiveness of T has been questioned in species that mainly metabolize this molecule to inactive metabolites, © 2014 John Wiley & Sons Ltd
suggesting that this drug would not be as suitable as an effective and safe treatment for pain in animals as it is in humans (de Sousa et al., 2008; Giorgi et al., 2009b). Although the effects of T have been evaluated in combination with different analgesic protocols (Ajadi et al., 2009; Lu et al., 2010, 2011) in pigs, its metabolism has never been tested in this species. Male pigs may experience pain following castration, tooth clipping and tail docking (Hay et al., 2003; Marchant-Forde et al., 2009; Torrey et al., 2009) as well as a result of condition such as arthritis and traumatic injuries (Zoric et al., 2003, 2009). Additionally, pig is an animal widely used as an experimental model for various surgical procedures (Cai et al., 2011; Polese et al., 2011). The necessity to test analgesic drugs to be used in this species during experimental procedures, often quite invasive, is thus imperative. Hence, the aim of this study was to assess the pharmacokinetics of T and its active metabolite M1 in male piglets after a single intramuscular administration. The study protocol was approved by the ethics committee of the University of Camerino, Italy (Authorization # 12014). The subjects were six healthy male Large White not suckling piglets, weighing from 7 to 8 kg, with an average age of 30 (5) days. Animals were administered T (5 mg/kg; Contramal, Gr€ uenthal, injectable solution 50 mg/mL) under fasting conditions by an intramuscular (i.m.) injection in the gluteal muscles. Blood (2 mL) was sampled from the jugular vein at 0, 1
2 C. Vullo et al.
Table 1. Pharmacokinetic parameters of tramadol and its metabolite (M1) following intramuscular injection of tramadol (5 mg/kg) in piglets (n = 6) Mean SD Parameters Lambda_z HL_Lambda_z Tmax Cmax AUC0–∞ Vz_F Cl_F AUMC0–∞ MRT0–∞
Unit 1/h h h lg/mL h*lg/mL mL/kg mL/h/kg h*h*lg/mL h
Tramadol 0.543 1.342 0.253 1.823 1.411 6754 3674 1.255 0.943
0.133 0.354 0.127 0.584 0.222 2234 563 0.087 0.065
M1 0.851 0.821 0.801 0.145 0.361 ND ND 0.551 1.645
0.134 0.146 0.124 0.044 0.092
calculated using the log-linear trapezoidal rule. Cmax, the highest observed plasma concentration, and Tmax, the time required to reach Cmax, were determined from the individual plasma concentration–time curves. The terminal half-life (HL_Lambda_z) was calculated from the slope of the logarithm of concentration versus time profile. Data were normally distributed (Shapiro–Wilk test) and presented as mean (SD). The dose used in the study was an extrapolation from the dose used in donkeys (Giorgi et al., 2009c). Based on allometric scaling principles, the dose requirements for a smaller animal should be more than that of a larger animal. Also, scaling is expected to have its greatest application to drugs that are eliminated by a single process such as glomerular filtration (Baggot, 2001). T is mainly eliminated by the kidneys. Therefore, the i.m. dose of 5 mg/kg, double of the dose given donkey in the Giorgi et al. (2009a,b,c) study was chosen. The mean plasma profiles of T and M1, following i.m. administration, are presented in Fig. 1. T plasma concentration was quantitatively detectable in all the piglets from 0.083 to 8 h (2.48–0.006 lg/ mL concentration range). M1 was quantifiable over a shorter time period (0.083–6 h) and in lower concentrations (0.203– 0.001 lg/mL concentration range). The active metabolite showed its Tmax at 0.821 h. Pharmacokinetic parameters are presented in Table 1. Plasma concentrations of T in piglets were similar to those reported for dogs administered with the same dose, while M1 plasma concentrations were almost doubled (Giorgi et al., 2010b). The mean clearance value was almost three times than that reported in dogs (Giorgi et al., 2010b). The average half-life value of T observed in this study was higher than that reported for dogs (0.73 h, Giorgi et al., 2010b) and lower than
2.5
2.0
1.5
Concentration (µg/mL)
0.083, 0.25, 0.50, 0.75, 1, 1.5 2, 4, 6, 8 and 10 h after drug administration by vacutainer blood collection test (BD Vacutainerâ Safety-Lok DB, Oxford, UK) in heparinized tubes. Plasma T concentrations were evaluated by HPLC detection method according to Giorgi et al., 2007. Briefly, the HPLC system was an LC 10ADvp-pump coupled to a RF-10A spectrofluorometric detector Workstation Prostar (Varian, Walnut Creek, CA, USA). Chromatographic separation was performed on a Luna C18 analytical column (150 mm 9 2.1 mm i.d., 5 lm particle size) maintained at 25 °C. The mobile phase consisted of acetonitrile:buffer (20 mM sodium dihydrogenphosphate, 30 mM SDS and 15 mM TEA adjusted to pH 3.9 with phosphoric acid) (40:60, v/v) at a flow rate of 1.5 mL/min. Excitation and emission wavelengths were 275 and 300 nm, respectively. T and sotalol hydrochloride [internal standard (IS)] were purchased from Sigma–Aldrich (St Louis, MO, USA); M1, was purchased from LGC Promochem (Milano, Italy). The analytical method was shortly validated for porcine plasma as follows. The standard curve was evaluated in addition to five quality control samples with three different concentrations for each series of analyses. The intra- and interday repeatability was measured as coefficient of variation and was lower than 5.1%, whereas accuracy, measured as closeness to the concentration added on the same replicates, was lower than 5.3%. The limit of detection (LOD) and lower limit of quantification (LLOQ) were determined using signal-to-noise ratios of 3 and 10, respectively. These parameters resulted in concentrations of 0.5 and 2 ng/mL, respectively. The pharmacokinetic calculations were carried out using WinNonLin v5.1 (Pharsight Corp, Cary, NC, USA). The noncompartmental model was used for plotting plasma concentrations of T and M1. Their relative pharmacokinetic parameters (Table 1) were determined using standard noncompartmental equations (Gabrielsson & Weiner, 2002). The AUC0–∞ was
1.0 0.4 0.3 0.2
T MEC (100 ng/mL)
0.1
0.129 0.087
Lambda_z, terminal phase rate constant; HL_Lambda_z, terminal halflife; Tmax, time of peak; Cmax, peak plasma concentration; AUC0–∞, area under the plasma concentration–time curve extrapolated to infinity; Vz_F, apparent volume of distribution; Cl_F, apparent plasma clearance; AUMC0–∞, area under the moment curve extrapolated to infinity; MRT0–∞, mean residence time extrapolated to infinity.
M1 MEC (40 ng/mL)
0.0 0
2
4
6
8
Time (h) Fig. 1. Observed mean plasma concentrations of tramadol (●) and its active metabolite (M1, 4) in piglets (n = 6) following single intramuscular injection of 5 mg/kg tramadol. Bars represent standard deviation of the mean. © 2014 John Wiley & Sons Ltd
Tramadol in piglets 3
those reported for both horses (1.5 h, Shilo et al., 2008) and llama (2.54 h, Cox et al., 2011). The absorption was rapid and comparable in the above-mentioned animal species with Tmax ranging 0.20–0.30 h. Tramadol (T) is a drug labelled for canine use. Because of the different metabolism and pharmacokinetics between animal species, the doses recommended for canine clinical use have been shown not suitable in other animal species (Giorgi et al., 2007, 2010a; de Sousa et al., 2008). T appears to possess a relatively safe profile; it is well tolerated with a low incidence of adverse effects in the animal species tested. However, the rapid achievement of high plasma concentrations of T and M1 has induced the ‘serotoninic storm’ effect in some animal species (Giorgi et al., 2007, 2010a,b; Cox et al., 2011). In this study, no objective adverse effects such as tremors, muscle fasciculation, ataxia and agitation were observed during the study period, although the drug adsorption was rapid (five of six animals showed a Tmax at the first collection point). This finding is in line with previous data in canine, equine and ovine species (de Sousa et al., 2008; Giorgi et al., 2009a,b). In comparison with dogs, horses and goats, piglets produced higher levels of M1. This difference could be due to variations in drug metabolism between the species (Martignoni et al., 2006) or to an immature drug metabolism system in piglets (Zuber et al., 2002). Given the importance of M1 in the T efficacy, the M1:T AUC ratio has been earlier used to speculate on the expected efficacy of this drug in different animal species. Its values in pigs are about 0.25. This value is similar to that reported in alpacas (Giorgi et al., 2010a), but lower than the one reported in cats (about 1, Pypendop & Ilkiw, 2008) and higher than that reported in dogs (0.02, Giorgi et al., 2010b; Kukanich & Papich, 2011). If the minimum effective concentration (MEC) reported in humans is assumed to also apply to piglets, it could be speculated that the drug efficacy (mainly due to the active metabolite) might exert its action over 3 h or longer. However, this assumption has to be made with the caveat that data extrapolation from humans to animals is not a sound practice (Giorgi, 2012). Relevant pharmacokinetic/pharmacodynamic (PK/PD) studies on T in this species should be conducted to evaluate whether this is a suitable analgesic drug for pigs/ piglets. In conclusion, findings of the present study show that T might have suitable pharmacokinetic features that make it amenable for use as pain reliever in piglets. However, prior to its use in piglets, additional specific studies on both the PK/PD of T and any effect on consumer’s health are required.
ACKNOWLEDGMENTS This work was supported by athenaeum funds (ex 60% University of Pisa). Cooperlink fund (CII11A2FAV) supported the international cooperation (Ita-Kor). Any external funding did not support the preparation of manuscript. Authors thank Dr H. Owen (School of Veterinary Sciences, University of © 2014 John Wiley & Sons Ltd
Queensland, Australia) for the critical review and English editing of the manuscript.
CONFLICT OF INTEREST STATEMENT None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.
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4 C. Vullo et al. Giorgi, M., Del Carlo, S., Łebkowska-Wieruszewska, B., Kowalski, C.J. & Saccomanni, G. (2010b) Pharmacokinetics of tramadol and metabolites after injective administrations in dogs. Polish Journal of Veterinary Sciences, 13, 639–644. Hay, M., Vulin, A., Genin, S., Sales, P. & Prunier, A. (2003) Assessment of pain induced by castration in piglets: behavioral and physiological responses over the subsequent 5 days. Applied Animal Behaviour Science, 82, 201–218. KuKanich, B. & Papich, M.G. (2004) Pharmacokinetics of tramadol and the metabolite O-desmethyltramadol in dogs. Journal of Veterinary Pharmacology and Therapeutics, 27, 239–246. Kukanich, B. & Papich, M.G. (2011) Pharmacokinetics and antinociceptive effects of oral tramadol hydrochloride administration in Greyhounds. American Journal of Veterinary Research, 72, 256–262. Lintz, W., Erlacßin, S., Frankus, E. & Uragg, H. (1981) Biotransformation of tramadol in man and animal. Arzneimittel-Forschung, 31, 1932–1943. Lu, D.Z., Fan, H.G., Wang, H.B., Hu, K., Zhang, J.T. & Yu, S.M. (2010) Effect of the addiction of tramadol to a combination of tiletamina-zolazepam and xylazine for anaesthesia of miniature pigs. Veterinary Record, 167, 489–492. Lu, D.Z., Fan, H.G., Kun, M., Song, Z.L., Ming, Y.S., Sheng, J. & Wang, H.B. (2011) Antagonistic effect of atipamezole, flumazenil and naloxone following anaesthesia with xylazine, tramadol and tiletamine/zolazepam combinations in pigs. Veterinary Anaesthesia Analgesia, 38, 301–309. Marchant-Forde, J.N., Lay, D.C. Jr, McMunn, K.A., Cheng, H.W., Pajor, E.A. & Marchant-Forde, R.M. (2009) Postnatal piglet husbandry practices and well-being: the effects of alternative techniques delivered separately. Journal of Animal Science, 87, 1479–1492. Martignoni, M., Groothuis, G.M. & de Kanter, R. (2006) Species differences between mouse, rat, dog, monkey and human CYP-mediated drug metabolism, inhibition and induction. Expert Opinion in Drug Metabolism and Toxicology, 2, 875–894. Polese, L., Angriman, I., Mungo, B., Luisetto, R., Frego, M., Merigliano, S. & Norberto, L. (2011) Ileorectal bypass performed entirely through
a transanal route in a porcine model. Surgical Endoscopy, 25, 3022–3027. Pypendop, B.H. & Ilkiw, J.E. (2008) Pharmacokinetics of tramadol, and its metabolite O-desmethyl-tramadol, in cats. Journal of Veterinary Pharmacology and Therapeutics, 31, 52–59. Raffa, R.B., Friderichs, E., Reimann, W., Shank, R.P., Codd, E.E. & Vaught, J.L. (1992) Opioid and nonopioid components independently contribute to the mechanism of action of tramadol, an ‘atypical’ opioid analgesic. Journal of Pharmacology and Experimental Therapeutics, 260, 275–285. Shilo, Y., Britzi, M., Eytan, B., Lifschitz, T., Soback, S. & Steinman, A. (2008) Pharmacokinetics of tramadol in horses after intravenous, intramuscular and oral administration. Journal of Veterinary Pharmacology and Therapeutics, 31, 60–65. de Sousa, A.B., Santos, A.C., Schramm, S.G., Porta, V., G orniak, S.L., Florio, J.C. & de Souza Spinosa, H. (2008) Pharmacokinetics of tramadol and O-desmethyltramadol in goats after intravenous and oral administration. Journal of Veterinary Pharmacology and Therapeutics, 31, 45–51. Souza, M.J. & Cox, S.K. (2011) Tramadol use in zoologic medicine. Veterinary Clinics of North America: Exotic Animal Practice, 14, 117– 130. Torrey, S., Devillers, N., Lessard, M., Farmer, C. & Widowski, T. (2009) Effect of age on the behavioral and physiological responses of piglets to tail docking and ear notching. Journal of Animal Science, 87, 1778–1786. Zoric, M., Stern, S., Lundeheim, N. & Wallgren, P. (2003) Four-year study of lameness in piglets at a research station. The Veterinary Record, 153, 323–328. Zoric, M., Nilsson, E., Lundeheim, N. & Wallgren, P. (2009) Incidence of lameness and abrasions in piglets in identical farrowing pens with four different types of floor. Acta Veterinaria Scandinavica, 51, 23. Zuber, R., Anzenbacherova, E. & Anzenbacher, P. (2002) Cytochromes P450 and experimental models of drug metabolism. Journal of Cellular and Molecular Medicine, 6, 189–198.
© 2014 John Wiley & Sons Ltd
SHORT COMMUNICATION
Pharmacokinetics of tramadol and its major metabolite after intramuscular administration in piglets C. VULLO* T.-W. KIM
†
M. MELIGRANA* C. MARINI* & M. GIORGI
‡
*School of Biosciences and Veterinary Medicine, University of Camerino, Matelica, Macerata, Italy; †College of Veterinary Medicine, Chungnam National University, Daejeon, South Korea; ‡Department of Veterinary Sciences Via Livornese (lato monte), San Piero a Grado, Pisa, Italy
Vullo, C., Kim, T.-W., Meligrana, M., Marini, C., Giorgi, M. Pharmacokinetics of tramadol and its major metabolite after intramuscular administration in piglets. J. vet. Pharmacol. Therap. doi: 10.1111/jvp.12133. Tramadol (T) is a centrally acting atypical opioid used for treatment of dogs. Piglets might experience pain following castration, tooth clipping and tail docking and experimental procedures. The aim of this study was to assess the pharmacokinetics of T and its active metabolite M1 in male piglets after a single intramuscular injection. Six healthy male piglets were administered T (5 mg/kg) intramuscularly. Blood was sampled at scheduled time intervals and drug plasma concentrations evaluated by a validated HPLC method. T plasma concentration was quantitatively detectable from 0.083 to 8 h. M1 was quantified over a shorter time period (0.083–6 h) with a Tmax at 0.821 h. The study demonstrated that piglets produce a larger amount of M1 compared with dogs, horses and goats. The human minimum effective concentration of M1 (40 ng/mL) was exceeded for over 3 h in piglets. If it is assumed to also apply to piglets, it could be speculated that the drug efficacy might exert its action over 3 h or longer. This assumption has to be confirmed by further specific pharmacokinetic/pharmacodynamic studies. (Paper received 5 January 2014; accepted for publication 23 March 2014) Mario Giorgi, Department of Veterinary Sciences Via Livornese (lato monte), Pisa, 56122 San Piero a Grado, Italy. E-mail: [email protected]
Tramadol (T) is a centrally acting, atypical opioid that has been used clinically for the last three decades to treat pain in humans. T displays a low affinity for the mu- and delta-opioid receptors, and weaker affinity for the kappa-subtype; it also interferes with the neuronal release and re-uptake of serotonin and noradrenaline in descending inhibitory pathways (Raffa et al., 1992). The clinical efficacy of T administration is dependent from its metabolism, because of the different analgesic activities of its metabolites. In fact, O-desmethyl-tramadol hydrochloride (M1), the only active metabolite, is 200 times more affine at the mu-receptor than the parent drug T, accounting for most of the clinical effect (Raffa et al., 1992). The metabolism of this drug has been investigated in different species including rodents (Lintz et al., 1981), ruminants (de Sousa et al., 2008; Giorgi et al., 2010a; Cox et al., 2011), pets (KuKanich & Papich, 2004; Pypendop & Ilkiw, 2008; Giorgi et al., 2009a,b), horses (Giorgi et al., 2006, 2007, 2009c; De Leo et al., 2009) and zoo animals (Souza & Cox, 2011). Similar metabolites are produced in all these species but in different amounts. Despite its long-term use, our understanding and prediction of the time course of its pharmacological effects are still complicated by the presence of active metabolites and the coexistence of opioid and nonopioid mechanisms of action. The clinical effectiveness of T has been questioned in species that mainly metabolize this molecule to inactive metabolites, © 2014 John Wiley & Sons Ltd
suggesting that this drug would not be as suitable as an effective and safe treatment for pain in animals as it is in humans (de Sousa et al., 2008; Giorgi et al., 2009b). Although the effects of T have been evaluated in combination with different analgesic protocols (Ajadi et al., 2009; Lu et al., 2010, 2011) in pigs, its metabolism has never been tested in this species. Male pigs may experience pain following castration, tooth clipping and tail docking (Hay et al., 2003; Marchant-Forde et al., 2009; Torrey et al., 2009) as well as a result of condition such as arthritis and traumatic injuries (Zoric et al., 2003, 2009). Additionally, pig is an animal widely used as an experimental model for various surgical procedures (Cai et al., 2011; Polese et al., 2011). The necessity to test analgesic drugs to be used in this species during experimental procedures, often quite invasive, is thus imperative. Hence, the aim of this study was to assess the pharmacokinetics of T and its active metabolite M1 in male piglets after a single intramuscular administration. The study protocol was approved by the ethics committee of the University of Camerino, Italy (Authorization # 12014). The subjects were six healthy male Large White not suckling piglets, weighing from 7 to 8 kg, with an average age of 30 (5) days. Animals were administered T (5 mg/kg; Contramal, Gr€ uenthal, injectable solution 50 mg/mL) under fasting conditions by an intramuscular (i.m.) injection in the gluteal muscles. Blood (2 mL) was sampled from the jugular vein at 0, 1
2 C. Vullo et al.
Table 1. Pharmacokinetic parameters of tramadol and its metabolite (M1) following intramuscular injection of tramadol (5 mg/kg) in piglets (n = 6) Mean SD Parameters Lambda_z HL_Lambda_z Tmax Cmax AUC0–∞ Vz_F Cl_F AUMC0–∞ MRT0–∞
Unit 1/h h h lg/mL h*lg/mL mL/kg mL/h/kg h*h*lg/mL h
Tramadol 0.543 1.342 0.253 1.823 1.411 6754 3674 1.255 0.943
0.133 0.354 0.127 0.584 0.222 2234 563 0.087 0.065
M1 0.851 0.821 0.801 0.145 0.361 ND ND 0.551 1.645
0.134 0.146 0.124 0.044 0.092
calculated using the log-linear trapezoidal rule. Cmax, the highest observed plasma concentration, and Tmax, the time required to reach Cmax, were determined from the individual plasma concentration–time curves. The terminal half-life (HL_Lambda_z) was calculated from the slope of the logarithm of concentration versus time profile. Data were normally distributed (Shapiro–Wilk test) and presented as mean (SD). The dose used in the study was an extrapolation from the dose used in donkeys (Giorgi et al., 2009c). Based on allometric scaling principles, the dose requirements for a smaller animal should be more than that of a larger animal. Also, scaling is expected to have its greatest application to drugs that are eliminated by a single process such as glomerular filtration (Baggot, 2001). T is mainly eliminated by the kidneys. Therefore, the i.m. dose of 5 mg/kg, double of the dose given donkey in the Giorgi et al. (2009a,b,c) study was chosen. The mean plasma profiles of T and M1, following i.m. administration, are presented in Fig. 1. T plasma concentration was quantitatively detectable in all the piglets from 0.083 to 8 h (2.48–0.006 lg/ mL concentration range). M1 was quantifiable over a shorter time period (0.083–6 h) and in lower concentrations (0.203– 0.001 lg/mL concentration range). The active metabolite showed its Tmax at 0.821 h. Pharmacokinetic parameters are presented in Table 1. Plasma concentrations of T in piglets were similar to those reported for dogs administered with the same dose, while M1 plasma concentrations were almost doubled (Giorgi et al., 2010b). The mean clearance value was almost three times than that reported in dogs (Giorgi et al., 2010b). The average half-life value of T observed in this study was higher than that reported for dogs (0.73 h, Giorgi et al., 2010b) and lower than
2.5
2.0
1.5
Concentration (µg/mL)
0.083, 0.25, 0.50, 0.75, 1, 1.5 2, 4, 6, 8 and 10 h after drug administration by vacutainer blood collection test (BD Vacutainerâ Safety-Lok DB, Oxford, UK) in heparinized tubes. Plasma T concentrations were evaluated by HPLC detection method according to Giorgi et al., 2007. Briefly, the HPLC system was an LC 10ADvp-pump coupled to a RF-10A spectrofluorometric detector Workstation Prostar (Varian, Walnut Creek, CA, USA). Chromatographic separation was performed on a Luna C18 analytical column (150 mm 9 2.1 mm i.d., 5 lm particle size) maintained at 25 °C. The mobile phase consisted of acetonitrile:buffer (20 mM sodium dihydrogenphosphate, 30 mM SDS and 15 mM TEA adjusted to pH 3.9 with phosphoric acid) (40:60, v/v) at a flow rate of 1.5 mL/min. Excitation and emission wavelengths were 275 and 300 nm, respectively. T and sotalol hydrochloride [internal standard (IS)] were purchased from Sigma–Aldrich (St Louis, MO, USA); M1, was purchased from LGC Promochem (Milano, Italy). The analytical method was shortly validated for porcine plasma as follows. The standard curve was evaluated in addition to five quality control samples with three different concentrations for each series of analyses. The intra- and interday repeatability was measured as coefficient of variation and was lower than 5.1%, whereas accuracy, measured as closeness to the concentration added on the same replicates, was lower than 5.3%. The limit of detection (LOD) and lower limit of quantification (LLOQ) were determined using signal-to-noise ratios of 3 and 10, respectively. These parameters resulted in concentrations of 0.5 and 2 ng/mL, respectively. The pharmacokinetic calculations were carried out using WinNonLin v5.1 (Pharsight Corp, Cary, NC, USA). The noncompartmental model was used for plotting plasma concentrations of T and M1. Their relative pharmacokinetic parameters (Table 1) were determined using standard noncompartmental equations (Gabrielsson & Weiner, 2002). The AUC0–∞ was
1.0 0.4 0.3 0.2
T MEC (100 ng/mL)
0.1
0.129 0.087
Lambda_z, terminal phase rate constant; HL_Lambda_z, terminal halflife; Tmax, time of peak; Cmax, peak plasma concentration; AUC0–∞, area under the plasma concentration–time curve extrapolated to infinity; Vz_F, apparent volume of distribution; Cl_F, apparent plasma clearance; AUMC0–∞, area under the moment curve extrapolated to infinity; MRT0–∞, mean residence time extrapolated to infinity.
M1 MEC (40 ng/mL)
0.0 0
2
4
6
8
Time (h) Fig. 1. Observed mean plasma concentrations of tramadol (●) and its active metabolite (M1, 4) in piglets (n = 6) following single intramuscular injection of 5 mg/kg tramadol. Bars represent standard deviation of the mean. © 2014 John Wiley & Sons Ltd
Tramadol in piglets 3
those reported for both horses (1.5 h, Shilo et al., 2008) and llama (2.54 h, Cox et al., 2011). The absorption was rapid and comparable in the above-mentioned animal species with Tmax ranging 0.20–0.30 h. Tramadol (T) is a drug labelled for canine use. Because of the different metabolism and pharmacokinetics between animal species, the doses recommended for canine clinical use have been shown not suitable in other animal species (Giorgi et al., 2007, 2010a; de Sousa et al., 2008). T appears to possess a relatively safe profile; it is well tolerated with a low incidence of adverse effects in the animal species tested. However, the rapid achievement of high plasma concentrations of T and M1 has induced the ‘serotoninic storm’ effect in some animal species (Giorgi et al., 2007, 2010a,b; Cox et al., 2011). In this study, no objective adverse effects such as tremors, muscle fasciculation, ataxia and agitation were observed during the study period, although the drug adsorption was rapid (five of six animals showed a Tmax at the first collection point). This finding is in line with previous data in canine, equine and ovine species (de Sousa et al., 2008; Giorgi et al., 2009a,b). In comparison with dogs, horses and goats, piglets produced higher levels of M1. This difference could be due to variations in drug metabolism between the species (Martignoni et al., 2006) or to an immature drug metabolism system in piglets (Zuber et al., 2002). Given the importance of M1 in the T efficacy, the M1:T AUC ratio has been earlier used to speculate on the expected efficacy of this drug in different animal species. Its values in pigs are about 0.25. This value is similar to that reported in alpacas (Giorgi et al., 2010a), but lower than the one reported in cats (about 1, Pypendop & Ilkiw, 2008) and higher than that reported in dogs (0.02, Giorgi et al., 2010b; Kukanich & Papich, 2011). If the minimum effective concentration (MEC) reported in humans is assumed to also apply to piglets, it could be speculated that the drug efficacy (mainly due to the active metabolite) might exert its action over 3 h or longer. However, this assumption has to be made with the caveat that data extrapolation from humans to animals is not a sound practice (Giorgi, 2012). Relevant pharmacokinetic/pharmacodynamic (PK/PD) studies on T in this species should be conducted to evaluate whether this is a suitable analgesic drug for pigs/ piglets. In conclusion, findings of the present study show that T might have suitable pharmacokinetic features that make it amenable for use as pain reliever in piglets. However, prior to its use in piglets, additional specific studies on both the PK/PD of T and any effect on consumer’s health are required.
ACKNOWLEDGMENTS This work was supported by athenaeum funds (ex 60% University of Pisa). Cooperlink fund (CII11A2FAV) supported the international cooperation (Ita-Kor). Any external funding did not support the preparation of manuscript. Authors thank Dr H. Owen (School of Veterinary Sciences, University of © 2014 John Wiley & Sons Ltd
Queensland, Australia) for the critical review and English editing of the manuscript.
CONFLICT OF INTEREST STATEMENT None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.
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