Gerardo Reyes-García

Thiamine and Cyanocobalamin Relieve Neuropathic Pain in Rats: Synergy with Dexamethasone

Treatment of neuropathic pain is an area of largely unmet medical need. Therefore, this pain may require the development of novel drug entities. In the search for alternatives, B vitamins have been found to be a clinically useful pharmacological tool for patients with neuropathic pain. However, preclinical studies supporting this use are lacking. In this study, we assessed the possible antiallodynic effects of thiamine, pyridoxine, and cyanocobalamin as well as dexamethasone and their combination on spinal nerve ligation induced allodynia. Sub cutaneous administration of thiamine (75–600 mg/kg), pyridoxine (75–600 mg/kg), cyanocobalamin(0.75–6 mg/kg), and dexamethasone (4–32 mg/kg) significantly reduced tactile allodynia in rats. Maximal antiallodynic effects were reached with 600 mg/kg of thiamine (∼58%), 600 mg/kg of pyridoxine (∼22%), 6 mg/kg of cyanocobalamin (∼73%), and 32 mg/kg of dexamethasone (∼68%). Since a small antiallodynic effect was observed with pyridoxine, this drug was not further analyzed in the combinations. Coadministration of thiamine or cyanocobalamin and dexamethasone remarkably reduced spinal nerve ligation induced allodynia (∼90%), showing a synergistic interaction between either thiamine or cyanocobalamin and dexamethasone. Our data indicate that thiamine and pyridoxine as well as the combination of B vitamins and dexamethasone are able to reduce tactile allodynia in rats and suggest the possible clinical use of these drugs in the treatment of neuropathic pain in human beings.

Characterization of the potentiation of the antinociceptive effect of diclofenac by vitamin B complex in the rat

The role of vitamin B complex preparations as an analgesic adjuvant is controversial. Therefore, the purpose of the present study was to characterize the potentiation of the antinociceptive effect of diclofenac by a vitamin B complex preparation and its individual components by using the pain-induced functional-impairment model in the rat (PIFIR). Pain was produced by the intraarticular injection of uric acid in the right hind limb. Oral administration of diclofenac resulted in a dose-dependent antinociceptive effect. Oral administration of a vitamin B complex preparation containing thiamine (vitamin B(1)), pyridoxine (vitamin B(6)), and cyanocobalamin (vitamin B(12)) in a 1:1:0.01 proportion did not produce any antinociception by itself, but it significantly potentiated the effect of diclofenac. Coadministration of diclofenac with either thiamine or pyridoxine resulted in an antinociceptive effect similar to that of diclofenac alone. On the other hand, coadministration of cyanocobalamin significantly increased diclofenac-induced antinociception. It is concluded that the potentiation of diclofenac-induced antinociception in the PIFIR model is due to cyanocobalamin.

Synergism between tramadol and meloxicam in the formalin test involves both opioidergic and serotonergic pathways

This study was designed to evaluate the antinociceptive interaction of the tramadol–meloxicam combination in different proportions (tramadol + meloxicam in 1:1, 1:3, and 3:1 ratios), as well as the role of nitric oxide, opioidergic, and serotonergic pathways in the antinociceptive effect of the combination. The effects of individual drugs and fixed‐ratio combinations were assayed using the 3% formalin test in mice. Isobolographic analysis was employed to characterize the synergism produced by the combinations. Tramadol (3.16–10 mg/kg, i.m.), meloxicam (3.16–17.8 mg/kg, i.m.), and tramadol–meloxicam combinations produced a dose‐dependent antinociceptive effect. ED30 values were estimated for the individual drugs, and isobolograms were constructed. The tramadol + meloxicam 1:1 and 1:3 ratio combinations showed synergistic interactions while the 3:1 ratio produced additive effects. Naloxone (1 mg/kg, i.m.) or methiothepin (0.1 mg/kg, i.m.), but not L‐NAME (3 mg/kg, i.m.), prevented the antinociceptive effects of the combination. These data suggest that (1) the tramadol–meloxicam combination produces a functional synergistic interaction that involves both opioid and serotonin receptors, and (2) this combination may be a promising tool in pain management. Drug Dev Res 73: 43–50, 2012.

Further evidence for interethnic differences in the oral pharmacokinetics of meloxicam.

AbstractIntroduction: Meloxicam is a nonsteroidal anti-inflammatory agent used widely in therapeutics. It is mainly metabolised by the cytochrome P450 enzyme (CYP) 2C9, with minor involvement of CYP3A4. So far, no information on the oral pharmacokinetics of this drug in adult Mexicans is available. The purpose of this study was to evaluate the oral pharmacokinetics of meloxicam in Mexican subjects. Methods: Twenty-four healthy male subjects received an oral dose of meloxicam 7.5mg after fasting for 10 hours. Blood samples were drawn from a suitable forearm vein and plasma obtained. The meloxicam concentration was evaluated by a high-performance liquid Chromatographic method and pharmacokinetic parameters were obtained by non-compartmental techniques. Pharmacokinetic parameters obtained in this study were compared with those reported under similar conditions in other populations in order to establish if interethnic differences in the pharmacokinetics of meloxicam exist. Results: After administration of meloxicam, plasma levels increased to a maximum concentration (Cmax) of 0.702 ± 0.027 (mean ± SEM) μg/mL with a time to reach Cmax of 4.77 ± 0.65h. The area under the plasma concentration versus time curve was 24.82 ± 1.23 μg · h/mL. The clearance was about 4.8 mL/min and the volume of distribution 9.8 ± 0.36L. When these parameters were compared with those reported in German and Indian subjects, a reduced clearance and volume of distribution were evident in Mexicans. However, clearance and volume of distribution obtained in this study were very similar to those reported in Chinese subjects. Conclusions: The oral pharmacokinetic parameters of meloxicam in healthy Mexican subjects compared with historic controls reported in other populations showed a reduced clearance and volume of distribution when compared with German subjects, whereas no differences between Mexican and Chinese subjects were observed. These results suggest that there are interethnic differences in the pharmacokinetics of meloxicam.

Pyritinol reduces nociception and oxidative stress in diabetic rats

The purpose of this study was to assess the antinociceptive and antiallodynic effect of pyritinol as well as its possible mechanism of action in diabetic rats. Streptozotocin (50 mg/kg) injection caused hyperglycemia within 1 week. Formalin-evoked flinching was increased in diabetic rats as compared to non-diabetic rats. Oral acute administration of pyritinol (50-200 mg/kg) dose-dependently reduced flinching behavior in diabetic rats. Moreover, prolonged administration of pyritinol (12.5-50 mg/kg, every 2 days for 2 weeks) reduced formalin-induced nociception. 1H-[1,2,4]-oxadiazolo [4,3-a] quinoxalin-1-one (ODQ, a guanylyl cyclase inhibitor, 2 mg/kg, i.p.), but not naltrexone (a non-selective opioid receptor antagonist, 1 mg/kg, s.c.) or indomethacin (a non-selective cycloxygenase inhibitor, 5 mg/kg, i.p.), blocked the pyritinol-induced antinociception in diabetic rats. Given alone ODQ, naltrexone or indomethacin did not modify formalin-induced nociception in diabetic rats. Oral acute (200 mg/kg) or prolonged (25 mg/kg, every 2 days for 2 weeks) administration of pyritinol significantly reduced streptozotocin-induced changes in free carbonyls, dityrosine, malondialdehyde and advanced oxidative protein products. Four to 8 weeks after diabetes induction, tactile allodynia was observed in the streptozotocin-injected rats. On this condition, oral administration of pyritinol (50-200 mg/kg) reduced tactile allodynia in diabetic rats. Results indicate that pyritinol is able to reduce formalin-induced nociception and tactile allodynia in streptozotocin-injected rats. In addition, data suggest that activation of guanylyl cyclase and the scavenger properties of pyritinol, but not improvement in glucose levels, play an important role in these effects.

Ketorolac tromethamine improves the analgesic effect of hyoscine butylbromide in patients with intense cramping pain from gastrointestinal or genitourinary origin.

The symptomatic treatment of pain associated with spasm of gastrointestinal or genitourinary origin can include the use of spasmolytic agents and/or non-steroidal anti-inflammatory drugs. However, the evidence of a superior effectiveness of combination in comparison with individual drugs is scarce and controversial. A double-blind, randomised, clinical trial study was designed to characterize the analgesic effect and safety of ketorolac and hyoscine butylbromide against hyoscine butylbromide alone in patients with ambulatory acute cramping pain of gastrointestinal and genitourinary origin. 160 patients with a pain level ≥4 in a 1-10 cm visual analogue scale were allocated to receive a fixed dose of ketorolac/hyoscine butylbromide (10 mg/20 mg) or hyoscine butylbromide (20 mg) alone at 6 h intervals, during a 48 h period. Both treatments were similarly effective when compared as a whole or when groups were classified by pain origin. Conversely, when treatments were grouped by pain intensity, ketorolac/hyoscine butylbromide combination showed a significant better pain relief profile than hyoscine butylbromide alone in pain intensity ≥7, but not <7. Data indicate that the oral ketorolac/hyoscine butylbromide mixture could be a better option than hyoscine butylbromide alone in the treatment of some acute intense cramping painful conditions.

Simple Method for the Determination of Cefaclor in Human Plasma Samples by HPLC

Abstract A rapid and simple method for determination of cefaclor in human plasma samples, by high‐performance liquid chromatography (HPLC), was developed. This method includes a deproteinization with perchloric acid as extraction procedure. Plasma extracts were analyzed on a reversed phase column eluted with a mixture of acetonitrile and 0.01 M sodium dihydrogen phosphate solution, adjusted to pH 6.5 with potassium hydroxide (7:93, v/v), and detected by absorbance at 260 nm. Retention times for cefaclor and the internal standard were 5.2 and 7.2 min, respectively. The method was linear in the range of 0.5–30 µg/mL and the detection limit of the method was 100 ng/mL. This method was useful and suitable for determination of cefaclor after oral administration in healthy volunteers, and could be used for bioavailability and bioequivalence studies of the drug.

Evaluation of the interaction between tramadol and diclofenac in several models of nociception in the rat

Diclofenac and tramadol are drugs widely used for the treatment of pain. However, side effects may limit their use. As both drugs produce side effects that are dose‐dependent, it seems appropriate to combine them in order to reduce the requirements for efficacy and, consequently, side effects. The purpose of this study was to evaluate the possible synergistic effect of these drugs in three experimental models of nociception in the rat. Dose‐response curves for diclofenac and tramadol were constructed in three models, thermal hyperalgesia, formalin, and hot plate. From these curves, ED40 or ED30 (according to the model employed) values were obtained and isobolographic analyses were carried out based on 0.5:0.5 proportions. Synergistic interactions were observed in the thermal hyperalgesia and hot plate models and an additive interaction was obtained in the formalin test. These results suggest a good therapeutic potential of this combination in the treatment of pain. Drug Dev Res 72: 391–396, 2011.

Synergistic Interaction of Diclofenac, Benfotiamine, and Resveratrol in Experimental Acute Pain

This study was designed to evaluate the possible synergistic antinociceptive interactions between diclofenac, benfotiamine, and resveratrol on acetic acid‐induced nociception in mice. Isobolographic analyses were used to define the nature of the interactions between drugs. Diclofenac, benfotiamine, or resveratrol, as well as their combinations, produced a dose‐dependent antinociceptive effect. ED30 values were estimated for the individual drugs and isobolograms were constructed. Theoretical ED30 values for the combinations estimated from the isobolograms were 170.9±23.4, 4.9±1.0, and 173.3±11.8 mg/kg for the diclofenac+benfotiamine, diclofenac+resveratrol, or benfotiamine+resveratrol combination, respectively. These values were significantly higher than the actually observed ED30 values, which were 10.2±1.9, 0.3±0.1, and 5.3±0.8 mg/kg, respectively, indicating a synergistic interaction in the three combinations. Data indicate that low doses of the diclofenac+benfotiamine, diclofenac+resveratrol, or benfotiamine+resveratrol combination can interact synergistically to reverse acetic acid‐induced nociception and they may represent a therapeutic advantage for clinical treatment of inflammatory pain. Drug Dev Res 72: 397–404, 2011.