Ondansetron Alfentanil

Ondansetron reduces the analgesic efficacy of tramadoi and at ieast double the dose was required in one ciinicai study. This resuited in more vomiting despite the ondansetron. In contrast, in studies in healthy subjects, ondansetron had no effect on the analgesic effects of morphine and alfentanil. 

In a study in healthy subjects single doses of intravenous ondansetron 8 or 16 mg were found to have no effect on the sedation or ventilatory depression due to alfentanil (a continuous infusion of 0.25 to 0.75 micrograms/kg following a 5 microgram/kg bolus dose) and had no effect on the rate of recovery. Similarly, in another study, intravenous ondansetron 8 mg had no effect on the reaction of 8 healthy subjects to pres-... 

On theoretical grounds ondansetron (a S-HTj-receptor antagonist) might be expected to decrease the effects of drugs that reduce pain transmission because serotonin (5-HT) is thought to affect pain responses via presynap-tic 5-HTj receptors in the spinal dorsal horn. This has been demonstrated for tramadol, ch is not a pure opioid and also acts by enhancing the effects of serotonin and noradrenaline (norepinephrine). However, ondansetron had no effect on alfentanil or morphine analgesia in healthy subjects. 

The interaction between ondansetron and tramadol appears to be established and of clinical importance. Ondansetron may double the dose requirement of tramadol, and so result in increased emetic effects, consequently ondansetron does not appear to be the best antiemetic to use with tramadol. Although not tested, other 5-HT3-receptor antagonists would be expected to interact similarly. Ondansetron appears to have no effect on alfentanil or morphine. 

Dershwitz M, Di Biase PM, Rosow CE, Wilson RS, Sanderson PE, Joslyn AF. Ondansetron does not affect alfentanil-induced ventilatory depression or sedation. Anesthesiology (1992) 77,447-52,... 

Petersen-Felix S, Arendt-Nielsen L, Bak P, Bjerring P, Breivik H, Svensson P, Zbinden AM. Ondansetron does not inhibit the analgesic effect of alfentanil. BrJAnaesth (1994) 73,326-30. 

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