Pain-induced Functional Impairment Model Research Articles

Pharmacokinetics and pharmacodynamics of metamizol in co-administration with morphine under acute and chronic treatments in arthritic rats.

To investigate the relationship between metamizol pharmacokinetics and the antinociceptive effect produced after subcutaneous administration of metamizol (177.8 mg/kg) alone or in combination with morphine (3.2 mg/kg), under acute and chronic treatments. Antinociception was assessed using the pain-induced functional impairment model in rat (PIFIR). Serial blood samples were collected from the same animals to study the pharmacokinetics of metamizol. The co-administration of the drugs in single dose, confirmed the potentiation of their individual antinociceptive effects. When the drugs were administered alone following the chronic schedule, a pronounced tolerance development to their antinociceptive effects was found, whereas it was significantly attenuated when they were administered together. Metamizol pharmacokinetics was unaltered by the presence of morphine. Plasma concentrations of 4-methylaminoantipyrine, an active metabolite markedly decreased under chronic administration. The mechanism involved in the potentiation of the antinociceptive effect produced by the combination, cannot be explained by the interaction of morphine on metamizol pharmacokinetics. Other pharmacokinetic interactions along with known pharmacodynamic interactions in which metamizol active metabolites contribute, should be considered. The frequency of administration enhances tolerance development and induces metamizol elimination process.

Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats.

Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016. © 2016 Wiley Periodicals, Inc.

Antinociceptive effects of a new sigma-1 receptor antagonist (N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamide) in two types of nociception

Pain has become an active clinical challenge due its etiological heterogeneity, symptoms and mechanisms of action. In the search for new pharmacological therapeutic alternatives, sigma receptors have been proposed as drug targets. This family consists of sigma-1 and sigma-2 receptors. The sigma-1 system is involved in nociception through its chaperone activity. Additionally, it has been shown that agonist to these receptors promote related sensitisation and pain hypersensitisation, suggesting the possible use of antagonists for sigma-1 receptors as an alternative therapy. The aim of this study was to evaluate the antinociceptive effect of a new sigma-1 receptor antagonist N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamida (NMIN) in two types of pain (arthritic and neuropathic) and to compare its efficacy and potency with reference drugs. The antinociceptive effects of NMIN were quantitatively evaluated using the pain-induced functional impairment model in the rat and the acetone test in a rat model of neuropathic pain. NMIN (sigma-1 receptor affinity of 324nM) did not show any antinociceptive activity in the arthritic pain model but showed a dose-dependent anti-allodynic effect in neuropathic pain. NMIN showed a similar efficacy compared to the effects obtained with morphine and the sigma-1 antagonist BD-1063. However, these reference drugs showed increased potency compared with NMIN. Our results suggest that sigma-1 receptors may play an important direct role in neuropathic pain but not in arthritic pain, supporting the hypothesis that NMIN may be useful for the treatment of neuropathic pain.

Enhancement of Antinociception but not Constipation by Combinations Containing Tramadol and Metamizole in Arthritic Rats

The use of a combination of analgesics could provide an optimal pain treatment with minimal side effects. Combinations of tramadol and some nonsteroidal anti-inflammatory drugs have demonstrated synergistic antinociceptive effects as well as a significantly reduced occurrence of adverse effects. The purpose of this study was to investigate the antinociceptive and constipation effects of tramadol and metamizole alone or in combination in rats and to discern among the types of drug interactions that exist using dose-response curves and an isobolographic analysis. The antinociceptive effects of tramadol and metamizole, alone or in various combination ratios, were quantitatively evaluated using the "pain-induced functional impairment model in the rat." Additionally, the constipation effect was evaluated using the charcoal meal test. Tramadol (3.2-56.2 mg/kg) and metamizole (56.2-562.3 mg/kg) demonstrated a dose-dependent response with tramadol being more efficacious and potent than metamizole. Twenty-five different combinations of tramadol with metamizole were analyzed, and the evaluated combinations exhibited antinociceptive effects that were either additive or potentiative. An optimal combination was established with 3.2 mg/kg of tramadol and 316.2 mg/kg of metamizole. However, the constipation observed with this combination was more severe than that observed with the administration of tramadol alone. Our results reveal a possible interaction between the two drugs, which may be pharmacokinetic and/or pharmacodynamic in nature. The preclinical antinociceptive interaction and adverse effects produced by the combination of tramadol and metamizole suggests that caution should be exercised when using this combination in the clinical therapy of pain.

Evidence of mechanism of action of anti‐inflammatory/antinociceptive activities of acacetin

Acacetin is a bioflavonoid with pharmacological properties such as antinociceptive/anti-inflammatory activities. However, scientific evidence of its spectrum activity and mechanisms of action is unknown. Acacetin administered via i.p. was assessed using several nociceptive experimental models such as the writhing test, the formalin test and carrageenan paw oedema in the thermal plantar tests (Hargreaves method) in mice, as well as the pain-induced functional impairment model in rat (PIFIR model). Acacetin produced a significant and dose-dependent inhibition of the writhes with an ED50 = 20 mg/kg. Furthermore, acacetin inhibited licking and shaking associated with nociceptive behaviour mainly in the inflammatory phase of the formalin test. No significant differences were observed in the plantar test in mice, but a minor response was obtained in the PIFIR model. Animals receiving pre-treatment of WAY100635 (0.1 mg/kg, s.c.), flumazenil (3 mg/kg, i.p.) or naloxone (1 mg/kg, i.p.) partially reduced the antinociceptive response of acacetin in the writhing test. Presence of the inhibitors in the NO-cGMP-K(+) channel pathway did not modify the antinociceptive effect of acacetin in the writhing or the formalin test. Our data showed that systemic administration of acacetin decreased visceral and inflammatory nociception and prevented the formalin-induced oedema. In the mechanism of the acacetin antinociceptive effect, 5-HT1A, GABA/BDZs and opioid receptors but not the NO-cGMP-K(+) channel pathway seem to be involved. The data presented prove acacetin to be potentially useful in the therapy of pain-related diseases.

Characterization of the analgesic effect of paracetamol and caffeine combinations in the pain-induced functional impairment model in the rat.

The analgesic activities of paracetamol (100, 178, 316 and 562 mg kg-1), caffeine (10, 18, 32 and 56 mg kg-1) and combinations of these doses were tested on a pain-induced functional impairment model in the rat. Dysfunction of the right hind limb was induced by an intra-articular injection of 30% uric acid in the knee. Drugs were given orally and the recovery of functionality over time was considered as an expression of analgesia. Paracetamol alone induced a dose-dependent analgesic effect whereas caffeine alone did not show any activity at the assayed doses. Combinations of 316 mg kg-1 paracetamol with either 10, 18, 32 or 56 mg kg-1 caffeine yielded analgesic effects significantly greater than that of paracetamol alone. The highest potentiation was observed with a paracetamol-caffeine mixture of 316-32 mg kg-1. Caffeine coadministration, however, did not significantly change paracetamol plasma levels. No potentiation was obtained with other combinations. Paracetamol plasma levels and analgesic effect observed with administration of 316 mg kg-1 paracetamol alone or 316-32 mg kg-1 of paracetamol-caffeine were fitted to the sigmoidal Emax model according to the Hill equation. The curves obtained were parallel, but that of the combination was shifted to the left. It is concluded that caffeine is able to potentiate the analgesic effect of paracetamol by a pharmacodynamic mechanism, but this only occurs at certain dose combinations.

Usefulness of the pain-induced functional impairment model to relate plasma levels of analgesics to their efficacy in rats.

In this work we show that the pain-induced functional impairment model (PIFIR) can be used with cannulated rats as a useful procedure for pharmacokinetic/pharmacodynamic modelling. This model evaluates analgesia by measuring motor impairment of the right limb after intra-articular administration of uric acid. Time of contact with a rotating cylinder is referred to the control limb. We studied the pharmacokinetic and pharmacodynamics of naproxen after six peroral doses to Wistar rats, and we examined the adjuvant action of caffeine with naproxen. Surgery and blood sampling did not produce any difference on functional impairment either in rats without uric acid or in the dysfunction produced by uric acid. The relation between naproxen plasma concentration and the analgesic effect was obtained with few rats. Caffeine alone did not produce any significant modification in functional impairment but the co-administration significantly increased the effect of naproxen. Plasma levels of naproxen did not change when caffeine was co-administered. The PIFIR model with blood sampling is a suitable method for pharmacokinetic/pharmacodynamic relationship studies and is specially useful to characterize drug-drug interactions.

Relationship between paracetamol plasma levels and its analgesic effect in the rat.

The relationship between plasma levels of paracetamol and its analgesic effect was studied in the rat using a model of pain-induced functional impairment (PIFI). Female Wistar rats received an intraarticular injection of 30% uric acid in the knee of the right hind limb, inducing its dysfunction. Animals then received oral paracetamol at doses of 178, 316 or 562 mg kg-1 and the recovery of functionality over time was considered as an expression of analgesia. Paracetamol plasma levels were determined by HPLC. Results showed that there is a direct relationship between paracetamol plasma levels and its analgesic effect that follows a sigmoidal model according to the Hill equation. The PIFI model appears to be a useful tool to establish pharmacokinetic/pharmacodynamic relationships for non-narcotic analgesics.

Potentiation of the Analgesic Effect of Tolmetin, a Potent Non-steroidal Anti-inflammatory Drug, by Caffeine in the Rat

The analgesic activities of tolmetin (0, 3, 10 and 32 mg kg−1), caffeine (0, 10, 18, 32 and 56 mg kg−1) and combinations of these doses were studied in the pain-induced functional impairment model in the rat. Tolmetin was able to produce a dose-dependent analgesic effect, whereas caffeine was ineffective in this model; 3–32, 3–56 and 10–56 mg kg−1 tolmetin-caffeine, but not other combinations, yielded analgesic effects which were significantly greater than those observed with tolmetin alone. However, tolmetin pharmacokinetics were not modified by caffeine co-administration. The results show that caffeine is able to potentiate the analgesic activity of tolmetin, probably by a pharmacodynamic mechanism of action, but only at selected dose combinations.

Hesperidin produces antinociceptive response and synergistic interaction with ketorolac in an arthritic gout-type pain in rats

Hesperidin occurs in greatest concentration in plants from the Rutaceae and Lamiaceae families. In human nutrition it contributes to the integrity of blood vessels and its deficiency in the diet has been linked to abnormal capillary leakiness as well as pain. In this study, the bioflavonoid hesperidin was identified as an active compound in an ethanol extract of the Rosmarinus officinalis aerial parts tested in the pain-induced functional impairment model in the rat (PIFIR) as an assay of inflammatory and chronic nociception similar to that observed in clinical gout. Hesperidin produced a dose-dependent and significant response with an ED 25 = 1666.72 mg/kg in comparison to an ED 25 = 302.90 mg/kg for the extract or an ED 25 = 0.47 mg/kg for the reference drug ketorolac in the PIFIR model. Although the antinociceptive response of R. officinalis was reverted in presence of the opioid antagonist naloxone (10 mg/kg, s.c.) and the 5HT 1A antagonist WAY100635 (0.12 mg/kg, s.c.), the hesperidin response was not modified by naloxone (10 mg/kg), WAY100635 (0.12 mg/kg), bicuculline (1 mg/kg, s.c.), flumazenil (10 mg/kg, i.p.) or caffeine (1 mg/kg, s.c.). Nevertheless, it was reduced in presence of capsazepine (10 or 20 mg/kg, s.c.) suggesting the participation of the TRPV1 receptor, which was reinforced when hesperidin significantly reduced the capsaicin-induced nociceptive response. A synergistic interaction was also observed when antinociceptive doses of hesperidin were combined with those of ketorolac producing 15 combinations mainly in additive and supra-additive responses. These results provide evidence for the antinociceptive activity of hesperidin and demonstrate synergistic response when combined with ketorolac, possibly by involvement of the TRPV1 receptor, suggesting their clinical potential in pain therapy.

Effect of metamizol on morphine pharmacokinetics and pharmacodynamics after acute and subchronic administration in arthritic rats

The aim of the present study was to investigate whether metamizol alters the pharmacokinetics of morphine and to determine the relationship between morphine plasma levels and antinociceptive effect produced after co-administration of drugs under acute and subchronic treatments using the pain-induced functional impairment model in rat (PIFIR model). Administration of morphine + metamizol under acute treatment produced a significantly higher antinociceptive effect than that obtained with morphine alone ( P < 0.05). This effect remained unaltered after subchronic treatments for 6 and 12 days. In addition, after the simultaneous administration of the drugs in a single dose, a pharmacokinetic interaction was found, which significantly ( P < 0.001) increased maximum plasma concentration ( C max), concentration at 4 h ( C 4h), partial areas under the plasma concentration–time curve from zero to 4 h (AUC 0–4) and from zero to 24 h (AUC 0–24). Moreover, whereas plasma concentration of morphine markedly decreased up to 4 h ( C 4h) after subchronic administration of the opioid, multiple dosing of the morphine + metamizol combination produced an accumulation of the drug in plasma ( P < 0.001). The increase observed in morphine plasma levels after co-administration of metamizol may be explained by a possible enzymatic inhibition of the glucuronosyl–transferase system involved in the metabolism of morphine. This study reveals both a pharmacodynamic and a pharmacokinetic interaction between morphine and metamizol, leading to an increased antinociceptive effect and a delay in tolerance development.

Antinociceptive activity of Annona diversifolia Saff. leaf extracts and palmitone as a bioactive compound

Annonas are consumed as fresh fruits, but are also widely used in folk medicine for treating pain and other ailments. Antinociceptive properties of the Annona diversifolia ethanol crude extract were tested using the pain-induced functional impairment model in rat (PIFIR) and the writhing test in mice. The ethanol extract caused a 25% recovery of limb function in rats; this response was significant and dose-dependent. Furthermore, this extract produced a similar antinociceptive response (ED 50 = 15.35 mg/kg) to that of the reference drug tramadol (ED 50 = 12.42 mg/kg) when evaluated in the writhing test in mice. Bio-guided fractionation yielded hexane and acetone active fractions from which the presence of palmitone and flavonoids was respectively detected. Palmitone produced an antinociceptive response with an ED 50 = 19.57 mg/kg in the writhing test. Antinociceptive responses from ethanol extract and tramadol were inhibited in the presence of either naloxone (1 mg/kg, s.c.)—an antagonist of endogenous opioids—or WAY100635 (0.8 mg/kg, s.c.)—a 5-HT 1A serotonin receptor antagonist. These results provide evidence that A. diversifolia possesses antinociceptive activity, giving support to their traditional use for treatment of spasmodic and arthritic pain. In addition, our results suggest the participation of endogenous opioids and 5-HT 1A receptors in this antinociceptive response.

Antinociceptive Effect and GC/MS Analysis ofRosmarinus officinalisL. Essential Oil from its Aerial Parts

The rationale of this investigation was to examine the antinociceptive properties of the essential oil obtained from Rosmarinus officinalis aerial parts, using a rat model of arthritic pain. The essential oil (100, 300 and 600 mg/kg, I. P.) produced a dose-dependent antinociceptive effect, manifested as a significant reduction in the dysfunction in the pain-induced functional impairment model in the rat (PIFIR model), mainly at high doses. Chemical constituents of the essential oil were further analyzed by gas chromatography-mass spectrometry (GC/MS). The major compounds in the essential oil were alpha-pinene (14.10 %), camphene (11.47 %), beta-pinene (12.02 %), myrcene (3.31 %), alpha-phellandrene (7.87 %), eucalyptol (8.58 %), 2-bornanone (3.42 %), camphor (8.75 %), isoborneol (3.48 %), borneol (4.85 %) and borneol acetate (6.49 %). The antinociceptive effects of R. officinalis essential oil were tested in combination with 0.12 mg/kg WAY100635, s. c. (an antagonist of 5-HT(1A) receptors) or 1 mg/kg naloxone, i. p. (an antagonist of endogenous opioids receptors), demonstrating in both cases an inhibition of the antinociceptive response. This study suggests an involvement, at least in part, of the serotonergic system via 5-HT(1A) receptors and endogenous opioids in the antinociceptive effect of R. officinalis essential oil in the PIFIR model.

Antinociceptive activity of Tilia americana var. mexicana inflorescences and quercetin in the formalin test and in an arthritic pain model in rats

Tilia species are well known around the world for their properties in traditional medicine. Antinociceptive activity of hexane, methanol and aqueous extracts from Tilia americana var. mexicana inflorescences was evaluated in the pain-induced functional impairment model in rats (PIFIR). A preliminar 300 mg/kg dosage of aqueous extracts i.p., but not the same dose of methanol or hexane extract, produced an antinociceptive response in rats similar to that of tramadol (17.8 mg/kg i.p.). A dose–response curve from aqueous extract allowed the determination of ED 50 = 364.97 mg/kg in comparison to ED 50 = 10.35 mg/kg for tramadol in this model. A previous HPLC–DAD analysis corroborated by an HPLC–MS technique in this study demonstrated the flavonoid composition in this Tilia aqueous extract revealing the presence of glycosides mainly derived from quercetin. Thus, Tilia aqueous extract and quercetin were tested at 30 and/or 100 mg/kg dosages i.p. in the PIFIR and formalin models producing a significant and dose-dependent antinociceptive response resembling that produced by a total and a partial agonist of 5-HT 1A receptors like 8-OH-DPAT (0.1 mg/kg, s.c.) and buspirone (5 mg/kg, i.p.), respectively. In all the treatments, antinociceptive response was inhibited in the presence of WAY 100635 (0.12 mg/kg, i.p.). Our results support the analgesic activity of T. americana var. mexicana inflorescences attributed by folk medicine; they also indicate that quercetin is partly responsible for this pharmacological activity that is likely mediated by serotonin 5-HT 1A receptors.

The antinociceptive efficacy of morphine, metamizol, or their combination in an experimental rat model with different levels of inflammatory pain

The purpose of this work was to evaluate the antinociceptive efficacy of an optimal morphine and metamizol combination on different levels of nociception (levels I, II, and III) using the “Pain-induced functional impairment model in the rat”. The effect of acetylsalicylic acid was examined as a reference drug at the same levels of nociception. The antinociceptive effects produced by morphine (3.2 mg/kg s.c.) and metamizol (177.8 mg/kg s.c.) were studied either individually or in combination. The antinociceptive efficacies were expressed as either areas under the curve (AUCs), maximum effects as functionality index in percent of the time course, or the antinociceptive effects produced at 2 h after administration. Unlike morphine, the antinociceptive effects of acetylsalicylic acid decreased with increasing intensity of nociception. In summary, the analysis of antinociceptive efficacies produced by the co-administration of these drugs for different levels of nociception revealed that co-administration provided potentiated and better antinociceptive coverage throughout our observation time than did the individual drugs or the expected theoretical sum (using AUC or effects after 2 h). This is the first study to demonstrate that an optimal morphine and metamizol combination is able to produce potentiation of antinociceptive effects during intense pain.

Participation of the GABA/benzodiazepine receptor and the NO-cyclicGMP pathway in the “antinociceptive-like effects” of diazepam

The mechanism of action underlying the “analgesic activity” of diazepam remains unclear. In this study, the possible participation of the GABA/benzodiazepine receptor and the nitric oxide-cyclic GMP (NO-cGMP) pathway was assessed utilizing the pain-induced functional impairment model in the rat (PIFIR). Nociception was induced by an intra-articular injection of 15% uric acid. Diazepam (1 and 2 mg/kg, i.p.) reversed the dysfunction induced by uric acid. Flumazenil (10 mg/kg, i.p.), a GABA/benzodiazepine receptor antagonist, abolished the “antinociceptive-like effect” of diazepam (at 2 mg/kg). The “antinociceptive-like effect” of diazepam (at 2 mg/kg) was antagonized by the non-selective nitric oxide synthase (NOS) inhibitor, N ω- l-nitro-arginine methyl ester hydrochloride ( l-NAME, 5 mg/kg, s.c.) (but not by its inactive isomer), and by the selective neuronal NOS inhibitor, 7-nitroindazole (7-NI, 1 mg/kg, i.p). While, the NO precursor, l-arginine (125 mg/kg, s.c.), but not d-arginine (125 mg/kg, s.c.), increased the “antinociceptive-like effect” of a non-effective dose of diazepam (1 mg/kg). Methylene blue (10 mg/kg, i.p.), a guanylate cyclase inhibitor, also prevented the “antinociceptive-like effect” of diazepam (at 2 mg/kg). These results suggest that the GABA/benzodiazepine receptor and the NO-cGMP pathway participate in the “antinociceptive-like effect” of diazepam.

Evaluation of the antinociceptive effect of Rosmarinus officinalis L. using three different experimental models in rodents

The rationale of this investigation was to examine the antinociceptive effect of an ethanol extract of Rosmarinus officinalis (RO) aerial parts, using three different experimental models: acetic acid-induced writhing test and formalin test in mice; and a model of arthritic pain: “pain-induced functional impairment model in the rat (PIFIR model)”. The antinociceptive efficacies were evaluated using several dose–response curves and time courses. The antinociceptive effects from RO extract were compared with the antinociceptive effect of either tramadol (TR: 3.16–50 mg/kg, i.p. in mice, and 1.0–31.62 mg/kg, i.p. in rats) or acetylsalicylic acid (AA: 31.62–562.32 mg/kg, p.o.). RO extract (10–300 mg/kg, p.o.) significantly ( P < 0.001) reduced the number of writhing movement induced by the i.p. administration of acetic acid solution in a dose-dependent way (ED 50 = 108.84 mg/kg, whereas, TR showed an ED 50 = 12.38 mg/kg). In addition, RO extract (30–300 mg/kg) significantly ( P < 0.001) inhibited licking and shaking behaviours in both early (neurogenic pain) and in the late (inflammatory pain) phases of the formalin test. These effects were like those produced by TR. Concerning the results using the PIFIR model, RO extract (30–3000 mg/kg, p.o.) like either TR or AA, produced a significant ( P < 0.001) and dose-dependent antinociceptive response in rats (RO: ED 50 = 222.78 mg/kg versus TR: ED 50 = 11.06 mg/kg and AA: ED 50 = 206.13 mg/kg). These results strongly suggest that aerial parts of RO possess antinociceptive and anti-inflammatory activity, and reinforce the use of this plant in folk medicine.

Peripheral involvement of the nitric oxide–cGMP pathway in the indomethacin-induced antinociception in rat

The role of nitric oxide (NO) in the antinociceptive effect of indomethacin was assessed in the pain-induced functional impairment model in the rat (PIFIR model), a model of inflammatory and chronic pain similar to that observed in clinical gout. Oral administration of indomethacin (5.6 mg/kg), a nonselective cyclooxygenase inhibitor, significantly decreased the nociceptive response elicited by uric acid injected into the knee joint of the right hind limb (2.0±3.0 and 149.7±18.0 area units [au], in the absence and the presence of indomethacin, respectively). This effect of indomethacin was reduced in nearly 50% by local pretreatment with the nonselective inhibitor of NO synthase, N G- l-nitro-arginine methyl ester ( l-NAME) (72.9±10.7 vs. 149.7±18.0 au, P<0.05). On the other hand, local administration of l-arginine (a NO synthase substrate) or sodium nitroprusside (a non-enzymatic NO donor) each increased in almost 40% the antinociceptive effect of indomethacin (230.9±12.6 and 226.6±9.7 vs. 149.7±18.0 au, P<0.05), whereas d-arginine (the inactive isomer of arginine) had no effect on the indomethacin antinociceptive response (208.0±34.9 vs. 149.7±18.0 au). These results suggest that, the antinociceptive effect of indomethacin involves, at least in part, the NO–cyclic GMP pathway at peripheral level.

Pharmacokinetic–pharmacodynamic modeling considering spinal and peripheral actions of nonsteroidal antiinflammatory drugs to optimize the treatment of inflammation-induced pain

It has been documented that nonsteroidal antiinflammatory drugs (NSAIDs) exhibit pharmacological actions at both the peripheral and central levels. However, the actual participation of the mechanisms of action elicited at different anatomical sites after systemic NSAID administration is not clear. To gain further knowledge on this issue, the aim of the present work is to study the pharmacodynamics and pharmacokinetics of diclofenac, a NSAID prototype, using an integrative approach. We have previously documented that local diclofenac administration at the site of injury induces antinociception in the formalin test, as well as in the pain-induced functional impairment model in the rat. This effect is reduced by nitric oxide (NO) and cyclic GMP synthesis inhibitors, as well as by potassium channel blockers [1,2]. We therefore assayed the effect of oral (systemic) diclofenac in the formalin test after pretreatment with either NG-nitro-L-arginine Methyl ester (L-NAME), a NO synthesis blocker, or glibenclamide, a potassium channel blocker, given by two routes of administration: locally at the site of injury and intrathecally. L-NAME and glibenclamide given by these two routes significantly reduced oral diclofenac antinociception. These results suggest that, after systemic administration, effective diclofenac concentrations are achieved at the site of injury as well as at the spinal cord, and that in these two sites of action there is a participation of the L-arginine–NO–cyclic GMP–potassium channel pathway. In a second series of experiments, diclofenac was administered locally at the site of injury (peripheral location), intrathecally, and simultaneously at the site of injury, intrathecally. Isobolographic analysis showed that there is an additive interaction between the effects at the peripheral and spinal levels. It is then likely that, after systemic administration, the observed antinociceptive effect is the result of the sum of peripheral and central mechanisms. Thus, effective diclofenac concentrations at central sites achieved after systemic administration probably are considerably lower that those required to observe an antinociceptive effect after direct injection, due to the interaction of mechanisms elicited at different anatomical locations. Therefore, from a pharmacokinetic point of view, the various central and peripheral sites of action can be considered as the affected compartment. In a third experimental series, the pharmacokinetics and antinociceptive effect of diclofenac was assayed in the pain-induced functional impairment model in the rat, which allows a simultaneous determination of antinociception and blood drug concentration [3]. It appeared that there was no direct relationship between diclofenac in blood and antinociception. Antinociception, however, was significantly related to affect compartment concentrations estimated by pharmacokinetic–pharmacodynamic modeling, consistently with the earlier described pharmacodynamic results. Computer simulations using the derived pharmacokinetic–pharmacodynamic model showed that an oral formulation of diclofenac yielding a very fast absorption, and hence a high blood concentration peak, can optimize drug transfer to the affected compartment, resulting in a fast-onset, long-lasting antinociceptive response. Our results show that the study of NSAID pharmacodynamics and pharmacokinetics using an integrative approach is useful for the characterization of the mechanisms of action involved after systemic drug administration, yielding information that allows the optimization of dosing regimens.

Participation of the l-arginine–nitric oxide–cyclic GMP–ATP-sensitive K + channel cascade in the antinociceptive effect of rofecoxib

The antinociceptive effect of rofecoxib, a preferential inhibitor of cyclooxygenase-2, was assessed in the pain-induced functional impairment model in the rat. Systemic administration of rofecoxib generated a dose-dependent antinociceptive effect in rats injected with uric acid into the knee joint of the right hindlimb in order to produce nociception. Ipsilateral intra-articular pretreatment with N G- l-nitro-arginine methyl ester ( l-NAME, an inhibitor of nitric oxide (NO) synthesis), 1 H-(1,2,4)-oxadiazolo (4,2- a)quinoxalin-1-one (ODQ, an inhibitor soluble guanylyl cyclase), and the ATP-sensitive potassium channel blocker glibenclamide reversed the antinociceptive effect of rofecoxib p.o. However, ipsilateral intra-articular pretreatment with l-arginine (a NO substrate), or 3-morpholino-sydnonimine-HCl (SIN-1, a non-enzymatic donor of NO), potentiated the antinociceptive effect induced by rofecoxib. The present results suggest that, in addition to cyclooxygenase-2 inhibition, the antinociceptive effect of rofecoxib could also involve activation of the l-arginine–NO–cyclic GMP (cGMP) pathway, followed by opening of ATP-sensitive K + channels at the peripheral level.