Analgesic Action Of Paracetamol Research Articles

KV7 and TRPV1 channels: neuronal targets for the analgesic action of paracetamol

KV7 and TRPV1 channels: neuronal targets for the analgesic action of paracetamol

Central dopaminergic system plays a role in the analgesic action of paracetamol: Preclinical evidence.

Objective:Even after 100 years of discovery, the exact mechanisms for the analgesic action of paracetamol are under scanner. It was recently proposed that paracetamol may act through different mechanisms, especially altering the serotoninergic system. The main objective of this preclinical study was to verify the role of drugs modulating dopaminergic system (l-dopa, bromocriptine, olanzapine) on the analgesic effect of paracetamol.Materials and Methods:Thirty adult male albino mice were divided into five groups: distilled water (0.5 ml/25 g), paracetamol (200 mg/kg), levodopa (10 mg/kg) + paracetamol, bromocriptine (5 mg/kg) + paracetamol (200 mg/kg), and olanzapine (2 mg/kg) + paracetamol (200 mg/kg). All drugs were administered orally for 14 days. Eddy's hot plate and tail immersion tests were used to determine analgesic activity. Tests were conducted 1 h after the drug administration on the 14th day. After that, animals were sacrificed and brains were dissected out, to measure the levels of dopamine. Statistical comparisons among the groups were performed by one-way analysis of variance followed by Tukey-Kramer test.Results:Coadministration of l-dopa and bromocriptine with paracetamol increased the antinociceptive activity of paracetamol significantly, whereas coadministration of olanzapine with paracetamol decreased the analgesic activity of paracetamol in the Eddy's hot plate and tail immersion tests considerably. There was a significant increase (P < 0.001) in the levels of dopamine in the brains of mice, which received levodopa, bromocriptine, and paracetamol. However, it was opposite in the brains of animals which received olanzapine.Conclusion:The results suggest that analgesic action of paracetamol is influenced by dopaminergic system.

Paroxetine Augments while Naloxone Abolishes the Analgesic Effect of Paracetamol in Acute Nociceptive Pain in Mice

The mechanism(s) of analgesic action of paracetamol (acetaminophen; N-acetyl-p-aminophenol) remains controversial. Previous studies on rats suggested that the antinociceptive action of paracetamol might involve the central descending inhibitory pain pathways recruiting both a serotoninergic and an opioidergic system. This study explores this issue in mice using paroxetine, the most potent selective serotonin re-uptake inhibitor, and the nonselective opioid pure antagonist naloxone. Animals were divided into two main groups for two separate experiments, each subdivided into 3 subgroups. In both experiments; the first group served as control, the second group received paracetamol (200 mg/kg, i.p). In one experiment, the third group received paroxetine (20 mg/kg p.o for 7 days) before paracetamol. In the other experiment, animals of the third group were pretreated with naloxone (5 mg/kg, i.p) 30 min before paracetamol. The antinociceptive effect of paracetamol was tested using the hot plate test. Paracetamol displayed a significant antinociceptive activity that was augmented by pretreatment with paroxetine as was shown by maintenance of its effect beyond that shown by paracetamol alone. On the other hand, pretreatment with naloxone abolished paracetamol’s antinociceptive activity in the hot-plate test. These results extended the previous observation in rats that the antinociceptive effect of paracetamol involved activation of a central descending pain inhibitory pathway with serotonin and opioidergic peptides being potential mediators recruited.

The effect of fluorine substitution on the physicochemical properties and the analgesic activity of paracetamol.

The physicochemical properties and analgesic action of six fluorinated analogues of 4-hydroxyacetanilide (paracetamol) have been investigated. Fluorine substitution adjacent to the hydroxyl group increased lipophilicity and oxidation potential whilst substitution adjacent to the amide had little effect on lipophilicity but led to a greater increase in oxidation potential. Lack of coplanarity and conjugation of the amide group and aromatic ring was also apparent with the analogues that had fluorine in the 2 and 6 positions. Introduction of fluorine into the amide group of paracetamol increased the lipophilicity 4-fold and also increased the oxidation potential of paracetamol. ED50 values for analgesic activity in the phenylquinone-induced abdominal constriction test on male Swiss White mice showed that ring substitution by fluorine reduced activity, especially at the 2,6-positions. Introduction of fluorine into the amide group enhanced activity significantly. Correlation of the analgesic activity with the physicochemical properties indicated that conjugation (and planarity) of the amide group with the aromatic ring is essential for activity and that ease of oxidation may also be an important factor.

Effect of aroma and magnum hops extracts and paracetamol on antioxidant liver parameters in mice

Hop varieties that are mainly grown in Serbia are Magnum (German variety) and Aroma, which is grown only in the Vojvodina region. About the use of hops extracts as an auxiliary remedy there are divergent opinions. Our findings indicate that extracts of Magnum and Aroma varieties, among the others, enhance and prolong the analgesic action of paracetamol. For this reason we undertook a study of the effects of these extracts alone and in combination with paracetamol, along with the action of paracetamol alone, on the activity of the antioxidant enzymes GSHPx, CAT, Px, XOD, GSHR, glutathione content, LPx intensity, as well as activities of AST and ALT. Paracetamol in the dose applied exerted no influence on the investigated parameters and neither did ethanolic extract of Magnum variety. On the other hand, ethanolic extract of Aroma hops caused a significant reduction of GSH content. In combination with paracetamol, extracts of both Magnum and Aroma varieties reduced significantly the LPx intensity, activities of CAT and GSHPx, as well as GSH content in the liver homogenate. A significant increase in the AST value with respect to control was also observed. These findings indicate the disturbance in the functioning of hepatocytes, probably by decelarating metabolism and elimination of paracetamol.

Effect of aroma and magnum hops extracts and paracetamol on antioxidant liver parameters in mice

Hop varieties that are mainly grown in Serbia are Magnum (German variety) and Aroma, which is grown only in the Vojvodina region. About the use of hops extracts as an auxiliary remedy there are divergent opinions. Our findings indicate that extracts of Magnum and Aroma varieties, among the others, enhance and prolong the analgesic action of paracetamol. For this reason we undertook a study of the effects of these extracts alone and in combination with paracetamol, along with the action of paracetamol alone, on the activity of the antioxidant enzymes GSHPx, CAT, Px, XOD, GSHR, glutathione content, LPx intensity, as well as activities of AST and ALT. Paracetamol in the dose applied exerted no influence on the investigated parameters and neither did ethanolic extract of Magnum variety. On the other hand, ethanolic extract of Aroma hops caused a significant reduction of GSH content. In combination with paracetamol, extracts of both Magnum and Aroma varieties reduced significantly the LPx intensity, activities of CAT and GSHPx, as well as GSH content in the liver homogenate. A significant increase in the AST value with respect to control was also observed. These findings indicate the disturbance in the functioning of hepatocytes, probably by decelarating metabolism and elimination of paracetamol.

Reflecting on tragedy: A commentary on deaths of children in restraints

Paracetamol (acetaminophen) is the most commonly used analgesic in the world. Recently, a new view of its action has emerged: that paracetamol would be a pro-drug that should be metabolized by the FAAH enzyme into AM404, its active metabolite. However, this hypothesis has been demonstrated only in naive animals, a far cry from the clinical pathologic context of paracetamol use. Moreover, FAAH is a ubiquitous enzyme expressed both in the central nervous system and in the periphery. Thus, we explored: (i) the involvement of FAAH in the analgesic action of paracetamol in a mouse model of inflammatory pain; and (ii) the contributions of central versus peripheral FAAH in this action. The analgesic effect of paracetamol was evaluated in thermal hyperalgesia, mechanical allodynia and hyperalgesia induced by an intra-plantar injection of carrageenan (3%) in FAAH knock-out mice or their littermates. Moreover, the contribution of the central and peripheral enzymes was explored by comparing the effect of a global FAAH inhibitor (URB597) to that of a peripherally restricted FAAH inhibitor (URB937) on paracetamol action. Here, we show that in a model of inflammatory pain submitted to different stimuli, the analgesic action of paracetamol was abolished when FAAH was genetically or pharmacologically inhibited. Whereas a global FAAH inhibitor, URB597 (0.3 mg/kg), reduced the anti-hyperalgesic action of paracetamol, a brain-impermeant FAAH inhibitor, URB937 (0.3 mg/kg), had no influence. However, administered intracerebroventricularly, URB937 (5 μg/mouse) reduced the action of paracetamol. These results demonstrate that the supra-spinally-located FAAH enzyme is necessary for the analgesic action of paracetamol.

3,5-Disubstituted analogues of paracetamol. Synthesis, analgesic activity and cytotoxicity

Seven 3,5-disubstituted analogues of paracetamol were synthesised in order to compare their physicochemical, pharmacological and toxicological properties with those of paracetamol (4′-hydroxyacetanilide, acetaminophen). Oxidation of the phenolic structure is likely involved in the analgesic action of paracetamol as well as in its toxification by cytochrome P450. The effect of disubstitution adjacent to the phenolic hydroxyl group was studied in order to establish possible structure-activity relationships. 3,5-Substituents with electron-donating capacities ( R   CH 3,  OCH 3,  SCH 3) decreased the half-wave oxidation potential substantially by 0.07 V to 0.16 V, whereas electron-withdrawing substituents ( R   F,  Cl,  Br, or  I) increased the oxidation potential by 0.04 V to 0.06 V when compared to paracetamol. Electron-donating substituents ( R   CH 3,  OCH 3,  SCH 3) increased the mouse brain cyclooxygenase inhibiting capacity of paracetamol. Electron-withdrawing halogen substituents ( R   F,  Cl,  Br or  I) decreased this inhibiting capacity. In agreement with this, the in vivo analgesic activity of the 3,5-dihalogenated analogues was lower when compared to paracetamol. Electron-donating substituents ( R   CH 3,  OCH 3,  SCH 3) decreased the cytotoxicity of paracetamol, when measured as leakage of lactate dehydrogenase from freshly isolated rat hepatocytes, almost completely. Most 3,5-dihalogen substituents ( R   F,  Cl or  Br) diminished it slightly. The fourth electron-withdrawing substituent ( R   I) strongly lowered the cytotoxicity of paracetamol in this test system. In conclusion, a higher cyclooxygenase inhibitory potency of 3,5-disubstituted analogues of paracetamol seemed to correlate with a lower cytotoxicity. 3,5-Disubstituted analogues with electron-donating substituents might therefore be safer analgesics than paracetamol itself. The opposite probably applies to analogues of paracetamol with electron-withdrawing substituents at the 3- and 5- positions of the aromatic nucleus.

Involvement of brain serotonergic system in the analgesic action of paracetamol

Involvement of brain serotonergic system in the analgesic action of paracetamol