Ephedrine enhances analgesic effect of morphine

Can ephedrine pretreatment be effective in alleviating rocuronium injection pain?

OBJECTIVE

The aim of this randomized, double-blind, placebo-controlled study was to evaluate the effect of ephedrine pretreatment on the intensity of rocuronium injection pain when rocuronium was applied by timing principle and also to compare this effect with lidocaine and placebo.

SUBJECTS AND METHODS

120 American Society of Anesthesiology risk score I-II patients scheduled for elective surgery under general anesthesia were randomized into three groups to receive either 70 μg/kg ephedrine (ephedrine group, n = 40) or 0.5 mg/kg lidocaine (lidocaine group, n = 40) or 5 ml NaCl 0.9% (placebo group, n = 40) as pretreatment. Thirty seconds after pretreatment drugs, rocuronium 0.6 mg/kg was administered by the timing principle and rocuronium injection pain scores were recorded. Twenty seconds after rocuronium administration, anesthesia was induced with thiopental and the patient's trachea was intubated. Hemodynamic parameters and adverse effects were recorded.

RESULTS

The overall frequency of having pain was 82.5, 52.5 and 22.5% in placebo, ephedrine and lidocaine groups, respectively. Although the frequency of mild and moderate pain scores was higher in the ephedrine group than in the lidocaine group, this difference was not statistically significant (p = 0.032 and p = 0.001, respectively).

CONCLUSION

Although not as effective as lidocaine 0.5 mg/kg, 70 μg/kg ephedrine pretreatment was able to alleviate rocuronium injection pain when rocuronium was applied by timing principle.

Effects of alpha 2-adrenoceptor agonists dexmedetomidine and guanfacine on morphine analgesia and tolerance in rats

BACKGROUND

Alpha 2 (α(2))-adrenoceptor agonists may be useful for their potential to increase or prolong opioid analgesia while attenuating the development of opioid tolerance. The purpose of this study was to investigate the effects of dexmedetomidine and guanfacine (α(2)-adrenoceptor agonists) on morphine analgesia and tolerance in rats.

METHODS

Adult male Wistar albino rats weighing 195-205 g were used. To constitute morphine tolerance, animals received morphine (50 mg/kg) once daily for 3 days. After the last dose of morphine had been injected on day 4, morphine tolerance was evaluated by analgesia tests. The analgesic effects of dexmedetomidine (20 ug/kg), guanfacine (0.5 mg/kg), MK-467 (0.25 mg/kg), and morphine were estimated at 30-min intervals (0, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests.

RESULTS

Our findings indicate that dexmedetomidine and guanfacine attenuated the expression of morphine tolerance. In addition, administration of dexmedetomidine with morphine increased morphine analgesia. On the contrary, data suggested that MK-467 (an α(2)-adrenoceptor antagonist) decreased morphine analgesia and increased morphine tolerance in analgesia tests.

CONCLUSION

In conclusion, we observed that co-injection of dexmedetomidine or guanfacine with morphine attenuated the expression of tolerance to the analgesic effect of morphine and that dexmedetomidine enhanced the morphine analgesia.

Influence of prazosin and clonidine on morphine analgesia, tolerance and withdrawal in mice

Rapid development of tolerance and dependence limits the usefulness of morphine in long-term treatment. We examined the effects of clonidine (alpha(2)-adrenoceptor agonist) and prazosin (alpha(1)-adrenoceptor antagonist) on morphine analgesia, tolerance and withdrawal. Morphine tolerance was induced using a 3-day cumulative twice-daily dosing regimen with s.c. doses up to 120 mg/kg. Tolerance was assessed on day 4, as loss of the antinociceptive effect of a test dose of morphine (5 mg/kg). After 10 h, morphine withdrawal was precipitated with naloxone (1 mg/kg). Prazosin had no analgesic effect alone but dose-dependently potentiated morphine analgesia in morphine-naive mice. Another alpha(1)-adrenoceptor antagonist, corynanthine, had similar effects. Prazosin also increased the analgesic potency of the morphine test dose in morphine-tolerant mice. Naloxone-precipitated vertical jumping was not affected, but weight loss was reduced by prazosin. Acutely administered clonidine potentiated morphine analgesia and alleviated opioid withdrawal signs, as expected. We conclude that in addition to the already established involvement of alpha(2)-adrenoceptors in opioid actions, also alpha(1)-adrenoceptors have significant modulatory role in opioid analgesia and withdrawal.