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Preclinical Research The coadministration of non-steroidal anti-inflammatory drugs (NSAIDs) with medicinal plant extracts may increase anti-inflammatory activity, thus permitting the use of lower NSAID doses and limiting the side effects. The aim of this study was to explore the interactions between an ethanolic extract of M. chamomilla extract (MCE) with two NSAIDs, diclofenac and indomethacin on carrageenan-induced paw inflammation and gastric injury in rats. Diclofenac, indomethacin and MCE, or combinations with MCE produced an anti-inflammatory effect. Effective dose (ED) values were estimated for the individual drugs, and isobolograms were constructed. The final experimental ED values were 483.7 mg/kg for diclofenac + MCE combination, and 212.6 mg/kg for indomethacin + MCE. These values were lower (p < 0.05) than the theoretical ED values (1186.9 mg/kg for diclofenac + MCE combination, and 1183.8 mg/kg for indomethacin + MCE). These data suggest that the interactions between NSAIDs and MCE that mediate the anti-inflammatory effects at the systemic level are synergistic and may have therapeutic advantages for the clinical treatment of inflammatory processes. Drug Dev Res 78 : 360-367, 2017. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Aims: Recent evidence has shown that systemic administration of sulfonylureas and biguanides block the diclofenac-induced antinociception, but not the effect produced by indomethacin. However, there are no reports about the peripheral interaction between analgesics and the biguanides metformin and phenformin. Therefore, this work was undertaken to determine whether glibenclamide and glipizide and the biguanides metformin and phenformin have any effect on the peripheral antinociception induced by diclofenac and indomethacin., Main Methods: Diclofenac and indomethacin were administered locally in the formalin-injured rat paw, and the antinociceptive effect was evaluated using the 1% formalin test. To determine whether peripheral antinociception induced by diclofenac or indomethacin was mediated by either the ATP-sensitive K(+) channels or biguanides-induced mechanisms, the effect of pretreatment with the appropriates vehicles or glibenclamide, glipizide, metformin and phenformin on the antinociceptive effect induced by local peripheral diclofenac and indomethacin was assessed., Key Findings: Local peripheral injections of diclofenac (50-200 μg/paw) and indomethacin (200-800 μg/paw) produced a dose-dependent antinociception during the second phase of the test. Local pretreatment with glibenclamide, glipizide, metformin and phenformin blocked the diclofenac-induced antinociception. On the other hand, the pretreatment with glibenclamide and glipizide did not prevent the local antinociception produced by indomethacin. Nonetheless, metformin and phenformin reversed the local antinociception induced by indomethacin., Significance: Data suggest that diclofenac could activate the K(+) channels and biguanides-dependent mechanisms to produce its peripheral antinociceptive effects in the formalin test. Likewise, a biguanides-dependent mechanism could be activated by indomethacin consecutively to generate its peripheral antinociceptive effect., (Copyright © 2011 Elsevier Inc. All rights reserved.)

There is evidence that administration of sulfonylureas, such as glibenclamide and tolbutamide, blocks diclofenac-induced antinociception, suggesting that diclofenac activates ATP-sensitive K(+) channels. However, there is no evidence for the interaction between diclofenac and other hypoglycemic drugs, such as the biguanides metformin or phenformin. Therefore, this work was undertaken to determine whether two sulfonylureas, glibenclamide and glipizide, as well as two biguanides, metformin and phenformin, have any effect on the systemic antinociception that is induced by diclofenac and indomethacin using the rat formalin test as an animal model. Systemic injections of diclofenac (10 to 30mg/kg) and indomethacin (10 to 30mg/kg) produced dose-dependent antinociception during the second phase of the test. Systemic pretreatment with glibenclamide (3 and 10mg/kg), glipizide (3 and 10mg/kg), metformin (100 and 180mg/kg) or phenformin (100 and 180mg/kg) blocked diclofenac-induced systemic antinociception in the second phase of the test (P<0.05). In contrast, pretreatment with glibenclamide, glipizide, metformin or phenformin did not block indomethacin-induced systemic antinociception (P>0.05). These data suggest that diclofenac, but not indomethacin, activated K(+) channels and metformin and phenformin-dependent mechanisms, which resulted in systemic antinociceptive effects in the rat formalin test., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) used for the treatment of acute gout and inflammation. However, its use is limited due to side effects. Acemetacin is a prodrug of indomethacin that exhibits better gastric tolerability in preclinical and clinical trials. The aim of this study was to examine if the systemic administration of acemetacin involved the sequential participation of nitric oxide (NO) or K+ channel pathways to confer its antinociceptive effect, as compared to indomethacin. The antinociceptive effect of both drugs was studied with the formalin test. Equimolar doses of acemetacin or indomethacin were administered orally. The intraplantar administration of either L-NAME, glibenclamide, apamin or charybdotoxin plus indomethacin or acemetacin was studied using the formalin test and the anti-inflammatory and antihyperalgesic effects were measured. The antinociceptive effect of acemetacin or indomethacin was not significantly different when pretreatment with L-NAME, glibenclamide, apamin or charybdotoxin was done. The antihyperalgesic and antiinflammatory effects were also similar for both indomethacin and acemetacin. Our results suggest that the antinociceptive effect of indomethacin or acemetacin is not mediated by NO or K+ channel activation., (2010 Prous Science, S.A.U. or its licensors. All rights reserved.)

Background and Purpose: Acemetacin is a non-steroidal anti-inflammatory drug which is rapidly bioconverted to indomethacin, but produces significantly less gastric damage than indomethacin. This study was performed to investigate several possible mechanisms that could account for the gastrointestinal tolerability of acemetacin., Experimental Approach: The gastric and intestinal damaging effects of acemetacin and indomethacin were examined in the rat. Effects of the drugs on blood levels of leukotriene B(4) and thromboxane B(2), on leukocyte-endothelial adherence in post-capillary mesenteric venules, and on gastric expression of tumour necrosis factor-alpha (TNF-alpha) were determined. The two drugs were also compared for gastric toxicity in rats pretreated with inhibitors of COX-2 and NOS., Key Results: Acemetacin induced significantly less gastric and intestinal damage than indomethacin, despite markedly suppressing COX activity. Indomethacin, but not acemetacin, significantly increased leukocyte adherence within mesenteric venules, and gastric expression of TNF-alpha. Pretreatment with L-nitro-arginine methyl ester or lumiracoxib increased the severity of indomethacin-induced gastric damage, but this was not the case with acemetacin., Conclusions and Implications: The increased gastric and intestinal tolerability of acemetacin may be related to the lack of induction of leukocyte-endothelial adherence. This may be attributable to the reduced ability of acemetacin to elevate leukotriene-B(4) synthesis and TNF-alpha expression, compared to indomethacin, despite the fact that acemetacin is rapidly bioconverted to indomethacin after its absorption.

It has been shown that the association of opioids analgesic agents with non-steroidal anti-inflammatory drugs (NSAIDs) can increase their antinociceptive activity, allowing the use of lower doses and thus limiting side effects. Therefore, the goal of the present study was to examine the possible pharmacological interaction between acemetacin and two opioids in the Hargreaves model of thermal hyperalgesia in the mouse. Acemetacin, codeine, nalbuphine or fixed-dose ratios acemetacin-codeine and acemetacin-nalbuphine combinations were administrated systemically to mice and the antihyperalgesic effect was evaluated using the thermal hyperalgesia test. All treatments produced a dose-dependent antihyperalgesic effect. ED40 values were estimated for all the treatments and an isobologram was constructed. The derived theoretical ED40 for the acemetacin-codeine and acemetacin-nalbuphine combinations were 55.9+/-4.9 mg/kg and 40.3+/-3.8 mg/kg, respectively, being significantly higher than the actually observed experimental ED40, 14.5+/-1.7 mg/kg and 12.7+/-2.2 mg/kg, respectively. These results correspond to synergistic interactions between acemetacin and opioids on the Hargreaves model of thermal hyperalgesia. Highest doses of the individual drugs or the combinations did not affect motor coordination in the balancing test on a rota-rod. Data suggest that low doses of the acemetacin-opioids combination can interact synergistically at systemic level and therefore this drugs association may represent a therapeutic advantage for the clinical treatment of inflammatory pain.

The aim of this study was to examine if the peripheral antinociceptive effects of diclofenac and indomethacin involve the sequential participation of NO and cGMP synthesis followed by potassium channel opening. The peripheral antinociceptive effects of diclofenac, indomethacin, pinacidil (a potassium channel opener) and atrial natriuretic peptide (ANP, which increases cGMP content in a NO-independent manner) were assayed using the formalin test in the rat. All compounds produced significant local antinociception. Diclofenac effect was reverted by N(G)-L-nitro-arginine methyl ester (L-NAME, an inhibitor of NO synthesis), by 1 H-(1,2,4)-oxadiazolo (4,2-a) quinoxalin-1-one (ODQ, an inhibitor soluble guanylyl cyclase), and by the potassium channel blockers glibenclamide, tolbutamide, charybdotoxin and apamin. Pinacidil effect was blocked by glibenclamide, tolbutamide, charybdotoxin and apamin, strongly suggesting that potassium channel opening results in antinociception. ANP effect was inhibited by the potassium channel blockers, but not by L-NAME, suggesting that potassium channel opening is a consequence of an increased cGMP content. Indomethacin was effective, but at doses higher than those of diclofenac, and could not be blocked by L-NAME nor by potassium channel blockers. The present results suggest that the L-arginine-NO-cGMP-potassium channel pathway is involved in the peripheral antinociceptive effect of diclofenac, but not of indomethacin, and thus provide evidence for differences in mechanisms of action among nonsteroidal antiinflammatory drugs (NSAIDs).