Abstract

Analgesic and Anti–Inflammatory Effects of Oxycodone with Adjuvant Drugs in an Experimental Study of Nociceptive and Neuropathic Pain

Author(s): Wojciech Leppert, Michal Szulc, Michal Kaczmarek, Martyna Rochowiak, Ewa Kaminska, Przemyslaw L. Mikolajczak

Objective

Opioids are often combined with adjuvants to treat symptoms that accompany pain and with adjuvant analgesics to treat neuropathic pain. Herein, we aim to investigate the analgesic and anti–inflammatory effects of oxycodone and selected adjuvants in rats.

Methods

Analgesic and anti–inflammatory effects of oxycodone were assessed after single subcutaneous (SC) (0.56 mg/kg) injections in rats, with the following drugs: midazolam (0.3 mg/kg), haloperidol (0.45 mg/kg), ketamine (0.3 mg/kg), hyoscine butylbromide (1.7 mg/kg), levomepromazine (0.35 mg/kg), and metoclopramide (1.0 mg/kg). Analgesia was assessed by the tail flick test. Anti–inflammatory activity was evaluated using a plethysmometer after carrageenan–induced edema. For neuropathic pain, analgesia was explored using the tail flick and von Frey tests. Neuropathic pain was induced by vincristine (0.1 mg/kg, i.p.) in male Wistar rats.

Results

All tested combinations of oxycodone with particular adjuvants showed increased analgesia in comparison to oxycodone alone. Compared to oxycodone alone, combinations with midazolam, haloperidol, hyoscine butylbromide, and levomepromazine prolonged analgesia. Anti–inflammatory activities were observed after co– administration of oxycodone paired with haloperidol and ketamine, which is a new aspect of the pharmacological profile of oxycodone. In the neuropathic pain model, vincristine lowered pain threshold in rats and inhibited growth of normal rat body weight. Oxycodone in combination with adjuvant analgesics showed more potent analgesia than oxycodone alone, especially in the tail–flick test. In most cases, the maximum effects were observed for 15–30 min since combined SC administration.

Conclusions

Analgesic and anti–inflammatory effects were observed in oxycodone combined with selected adjuvants in rats; although the mechanism of these interactions is not yet well understood. Further studies should test these combinations after chronic administration and assess the benefits and risks associated with the use of the tested combinations in humans.