Interaction of different antidepressants with acute and chronic methadone in mice, and possible clinical implications

Magnesium Salt, a Simple Strategy to Improve Methadone Analgesia in Chronic Pain: An Isobolographic Preclinical Study in Neuropathic Mice

Analgesic efficacy of methadone in cancer and chronic non-cancer pains is greater than that of other opioids, probably because of its unique pharmacokinetics properties and also because it targets glutamatergic receptors in addition to µ-opioid receptors. However, methadone has drawbacks which are clearly related to dosing and treatment duration. The authors hypothesized that the antinociceptive efficacy of methadone could be synergistically potentiated by magnesium and copper salts in a preclinical mouse model of chronic pain, using the intraplantar formalin test as algesimetric tool. The spared nerve injury mice model was used to generate mononeuropathy. A low dose (0.25%) formalin was injected in the neuropathic limb in order to give rise only to Phase I response, resulting from direct activation by formalin of nociceptive primary afferents. Licking/biting of the formalin-injected limb was evaluated as nociceptive behavior during a 35-min observation period. Dose-response curves for intraperitoneal magnesium sulfate (10, 30, 100, and 300 mg/kg i.p.), copper sulfate (0.1, 0.3, 1, and 3 mg/kg i.p.) and methadone (0.1, 0.3, 1, and 3 mg/kg i.p.) allowed to combine them in equieffective doses and to determine their interaction by isobolographic analysis. Magnesium sulfate, copper sulfate and methadone dose-dependently decreased the nociceptive response evoked by formalin injection, the respective ED₅₀ being 76.38, 1.18, and 0.50 mg/kg i.p. Isobolographic analysis showed a superadditive interaction for magnesium and methadone. Indeed, despite that both ED₅₀ are obviously equieffective, the ED₅₀ for the MgSO4/methadone combination contained less than one third of the methadone having the ED₅₀ for methadone alone. For the CuSO₄/methadone combination, the interaction was only additive. Extrapolated to clinical settings, the results suggest that magnesium salts might be used to improve synergistically the efficacy of methadone in neuropathy, which would allow to reduce the dose of methadone and its associated side effects.

Pharmacological interaction between NSAIDS with clomipramine and risperidone in mice visceral pain

Nonsteroidal anti-inflammatory drugs (NSAIDs) possess as primary action mechanism the inhibition of cyclooxygenases (COX-1, COX-2, and COX-3), thus producing a decreasing prostaglandin synthesis. This study was designed to evaluate whether the antinociception induced by NSAIDs could be modulated by clomipramine or risperidone using a chemical model of inflammatory acute visceral pain, the abdominal acetic acid induced a writhing test in mice. Dose-response curves, intraperitoneal, or intrathecal for the antinociceptive activity displayed by ketoprofen, piroxicam, nimesulide, parecoxib, and paracetamol were analyzed in order to obtain the ED₅₀ of each drug. Pretreatment of mice with either clomipramine or risperidone, increased antinociceptive potency of ketoprofen, piroxicam, nimesulide, parecoxib, and paracetamol, expressed by a decrease in the values of antinociceptive ED_50. The results that were obtained are in line with those where the inhibition of COXs provides a justification for most of the pharmacological actions. Nevertheless, several findings suggest other molecular mechanisms, among which may be mentioned, L-selecting shedding; inhibition of i-NOS; inhibition of NF-Kappa B; suppression metaloproteinasas; inhibition of ß2 integrin activation; activation of α₂ -adrenoceptor; increase of IL-1ß; upregulation IL-6. In conclusion, the data generated in this study demonstrated that risperidone and clomipramine, separately, increase antinociceptive potency of NSAIDs in a chemical model of inflammatory acute visceral tonic pain.

Interaction between methylphenidate, methadone and different antidepressant drugs on antinociception in mice, and possible clinical implications

OBJECTIVES

Methylphenidate (MPH), a psychostimulant used for treatment of attention deficit hyperactivity disorder (ADHD), is widely used by patients on antidepressants and methadone maintenance treatment (MMT). Preclinical studies showed MPH to exert analgesic effects when given alone or with morphine.

METHODS

Using the hotplate assay on mice, we studied the interaction of acute doses of MPH with sub-threshold doses of methadone and different antidepressant medications and the interaction of increasing doses of MPH with chronic methadone.

RESULTS

Adding a sub-threshold dose of venlafaxine, desipramine or clomipramine to MPH produced significant augmentation of MPH antinociception with each medication (P < 0.05). No such interactions were found between escitalopram and acute methadone. However, addition of increasing doses of MPH to chronic methadone given for 2 weeks using ALZET osmotic mini pumps induced augmentation of the antinociceptive effect of chronic methadone exclusively at high dose of MPH (7.5 mg/kg).

CONCLUSIONS

These findings may implicate the need of an excessive attention to the administration of MPH to MMT patients. The no interaction found between MPH and escitalopram may hint to the possibly safe co-administration of MPH and selective serotonin reuptake inhibitors (SSRIs) to depressed ADHD patients. Further studies are needed in order to validate these possible clinical implications.