Effects of naloxone and flumazenil on antinociceptive action of acetaminophen in rats

N-acetylcysteine dose-dependently improves the analgesic effect of acetaminophen on the rat hot plate test

BACKGROUND

Acetaminophen (APAP) induced hepatotoxicity is a clinically important problem. Up to now, interventive therapy with n-acetylcysteine (NAC) has been considered as a gold-standard treatment for APAP overdose. However, no study has focused on the efficacy of these drugs' concurrent administration on probable enhancing therapeutic outcomes. Thus, this study was aimed to investigate the analgesic effect of co-administration of NAC and acetaminophen in male rats. The NAC-APAP drug formulation may demonstrate the stranger antinociceptive effect.

METHODS

Forty-eight male Sprague-Dawley rats (12-14 weeks) randomly divided into six equal groups; control, APAP (received 300 mg/kg APAP), NAC (received 600 mg/kg NAC) and APAP+ NAC groups that received simultaneously 300 mg/kg APAP with 200-600 mg/kg NAC (AN200, AN400, AN600). All administrations were done orally for once. The antinociceptive effect was recorded by measurement of latency period on a hot plate in 30, 60, and 90 min after administrations.

RESULTS

The results showed that NAC's concurrent administration with APAP, dose-dependently increased APAP analgesic effects (p< 0.0001). Moreover, NAC treatment exhibited an antinociceptive effect in 60 and 90 min, per se. The treatments had no adverse effect on liver enzymes and oxidative stress.

CONCLUSION

Co-administration of NAC with APAP can improve the antinociceptive effect of APAP. It is suggested that this compound can enhance analgesic effects of APAP and eventually lead to a reduction in acetaminophen dose. Further studies are needed to evaluate the molecular mechanism of this hyper analgesic effect.

A Behavioral Study of Promethazine Interaction with Analgesic Effect of Diclofenac: Pain Combination Therapy

OBJECTIVES

Pain is considered as a cause of sickness and the most prevalent symptom which makes people visit a physician. Nowadays, combination therapy is becoming useful to relieve chronic and postsurgical pain. The aim of this study was to study the promethazine (as an antihistamine) interactions with antinociceptive effect of diclofenac (as a non-steroidal anti-inflammatory drugs).

METHODS

In initial part of the study, we investigate the analgesic effect of diclofenac. Using writhing test, we demonstrate that diclofenac significantly reduces writhe response induced by acetic acid in a dose-dependent manner. In this study, we evaluate the combination effect of promethazine on diclofenac analgesic effect.

RESULTS

We observed that diclofenac inhibited pain in the dose dependent manner which means that by increasing dose of diclofenac a significant decrease in pain was observed. This experimental setup allowed calculation of the dose that caused 50% antinociception (ED50) for diclofenac. The ED50 for diclofenac in this study was determined to be 9.1 mg/kg according our previous study. Additionally, promethazine was showed a dose-dependent inhibition of writhes. The combination of different doses of promethazine (2, 4, 6 mg / kg) with diclofenac ED50 (9.1 mg / kg) was injected to mice. Promethazine 4 and 6 mg / kg in combination with diclofenac had significantly led to increase analgesic effect of diclofenac.

CONCLUSION

In conclusion, these results add important information to the existing knowledge on combination of diclofenac and antihistamine in pain therapies to be used in clinical practice and maybe helpful in designing the future guidelines.

Arthropathy-related pain in a patient with congenital impairment of pain sensation due to hereditary sensory and autonomic neuropathy type II with a rare mutation in the WNK1/HSN2 gene: a case report

Background

Hereditary sensory and autonomic neuropathy (HSAN) type II with WNK1/HSN2 gene mutation is a rare disease characterized by early-onset demyelination sensory loss and skin ulceration. To the best of our knowledge, no cases of an autonomic disorder have been reported clearly in a patient with WNK/HSN2 gene mutation and only one case of a Japanese patient with the WNK/HSN2 gene mutation of HSAN type II was previously reported.

Case presentation

Here we describe a 54-year-old woman who had an early childhood onset of insensitivity to pain; superficial, vibration, and proprioception sensation disturbances; and several symptoms of autonomic failure (e.g., orthostatic hypotension, fluctuation in body temperature, and lack of urge to defecate). Genetic analyses revealed compound homozygous mutations in the WNK1/HSN2 gene (c.3237_3238insT; p.Asp1080fsX1). The patient demonstrated sensory loss in the “stocking and glove distribution” but could perceive visceral pain, such as menstrual or gastroenteritis pain. She experienced frequent fainting episodes. She had undergone exenteration of the left metatarsal because of metatarsal osteomyelitis at 18 years. Sural nerve biopsy revealed a severe loss of myelinated and unmyelinated nerves. She complained of severe pain in multiple joints, even on having pain impairment. Although non-steroidal anti-inflammatory drugs are generally more effective than acetaminophen for arthritis, in our case, they were ineffective and acetaminophen (2400 mg/day) adequately controlled her pain and improved quality of life. Over 3 months, the numerical rating scale, pain interference scale of the Brief Pain Inventory, and the Pain Catastrophizing Scale decreased from 6/10 to 3/10, from 52/70 to 20/70, and from 22/52 to 3/52 points, respectively.

Conclusions

This is the second reported case of a Japanese patient with WNK/HSN2 gene mutation of HSAN type II and the first reported case of an autonomic disorder in a patient with the WNK/HSN2 gene mutation. Acetaminophen adequately controlled arthropathy related pain in a patient with congenital impairment of pain sensation.

Hypothermic activity of acetaminophen; involvement of GABAA receptor, theoretical and experimental studies

OBJECTIVES

The mechanism of hypothermia action of acetaminophen (APAP) remains unclear even 125 years after its synthesis. Acetaminophen produces hypothermia. The mechanism of this reduction in core body temperature is not clear but evidence shows that it is not dependent on opioid and cannabinoid receptors. Because of strong documents about the roles of GABA and benzodiazepine receptors in hypothemic activity of some drugs such as diazepam, we determined if these receptors also contributes to the hypothermic effect of APAP.

MATERIALS AND METHODS

Diazepam (5 mg/kg, IP) was used for induction of hypothermia. Flumazenil (10 mg/kg, IP) or picrotoxin (2 mg/kg, IP) used for reversal of this effect. Rats injected with APAP (100, 200 or 300 mg/kg, IP). Baseline temperature measurements were taken with a digital thermometer via rectum. To evaluate the structural correlation between APAP and benzodiazepine receptor ligands, numerous models are selected and studied at HF/6-31G* level of theory. Relative energies, enthalpies and Gibbs free energies were calculated for all selected drugs.

RESULTS

Diazepam induced hypothermia was reversed by flumazenil or picrotoxin. Rats injected with APAP displayed dose- and time-related hypothermia. For combined administration, the hypothermic effect of APAP (200 mg/kg) was strongly reduced by pretreatment with picrotoxin or flumazenil P<0.0001and P<0.01, respectively. Selective structural data, bond length, dihedral angles, and related distance in pharmacophore of APAP and BZDR models were the same. Some significant structural analogues were obtained between these drugs.

CONCLUSION

Results suggest hypothermic action of acetaminophen may be mediate by its effect at GABAA benzodiazepine receptor.

Antinociceptive effects of vitexin in a mouse model of postoperative pain

Vitexin, a C-glycosylated flavone present in several medicinal herbs, has showed various pharmacological activities including antinociception. The present study investigated the antinociceptive effects of vitexin in a mouse model of postoperative pain. This model was prepared by making a surgical incision on the right hindpaw and von Frey filament test was used to assess mechanical hyperalgesia. Isobolographical analysis method was used to examine the interaction between vitexin and acetaminophen. A reliable mechanical hyperalgesia was observed at 2 h post-surgery and lasted for 4 days. Acute vitexin administration (3–10 mg/kg, i.p.) dose-dependently relieved this hyperalgesia, which was also observed from 1 to 3 days post-surgery during repeated daily treatment. However, repeated vitexin administration prior to surgery had no preventive value. The 10 mg/kg vitexin-induced antinociception was blocked by the opioid receptor antagonist naltrexone or the GABA_A receptor antagonist bicuculline. The doses of vitexin used did not significantly suppress the locomotor activity. In addition, the combination of vitexin and acetaminophen produced an infra-additive effect in postoperative pain. Together, though vitexin-acetaminophen combination may not be useful for treating postoperative pain, vitexin exerts behaviorally-specific antinociception against postoperative pain mediated through opioid receptors and GABA_A receptors, suggesting that vitexin may be useful for the control of postoperative pain.