Articles: narcotic-antagonists.
-
Randomized Controlled Trial Clinical Trial
Opioid-sparing effects of a low-dose infusion of naloxone in patient-administered morphine sulfate.
A naloxone infusion is effective in reducing epidural and intrathecal opioid-related side effects. The use of naloxone infusion concomitant with intravenous morphine patient-controlled analgesia (PCA) has not been evaluated, probably because of an expected direct antagonism of the systemic opioid effect. The authors compared the incidence of morphine-related side effects and the quality of analgesia from two small doses of naloxone infusion. ⋯ Naloxone is effective in preventing PCA opioid-related side effects. Naloxone infusion at 0.25 microg x kg(-1) x h(-1) not only attenuates these side effects but appears to reduce postoperative (beyond 4-8 h) opioid requirements. This dosing regimen can be prepared with 400 microg naloxone in 1,000 ml crystalloid given in 24 h to a patient weighing 70 kg.
-
Randomized Controlled Trial Clinical Trial Controlled Clinical Trial
Opiate and H1 antagonist effects on histamine induced pruritus and alloknesis.
Itching is a well known side-effect of opiate therapy. To gain insight into the possible contribution of opiate receptors to itching we compared the antipruritic effect of naltrexone (Nemexin), an opiate antagonist, to an H1-receptor antagonist and to placebo. In a double blind cross-over study on 15 healthy volunteers, 25 mg naltrexone or placebo was orally given 60 min prior to a histamine stimulus. ⋯ Both naltrexone and cetirizine significantly diminished histamine induced itching. In contrast to placebo and cetirizine, naltrexone abolished alloknesis completely in four of 15 volunteers and in the others alloknesis was greatly reduced after naltrexone. Since vascular reactions to histamine are of peripheral origin, whereas alloknesis depends on central nervous mechanisms, our findings suggest a pronounced centrally mediated action of naltrexone on histamine induced pruritus.
-
Comparative Study
Opiate receptors in the periaqueductal gray mediate analgesic effect of nitrous oxide in rats.
The site of action and the pathways which are activated by nitrous oxide (N2O) to produce an analgesic effect are not well defined. Experiments were designed to determine whether N2O produces analgesia by activating opiate receptors or alpha2-adrenoceptors in periaqueductal gray. The analgesic effect of N2O was determined using the tail flick response to noxious radiant heat in lightly anesthetized rats. ⋯ The increase in the tail flick latencies produced by N2O was reversed by bilateral microinjection into the ventrolateral part of periaqueductal gray with the opiate receptor antagonist naloxone 2.5 microg/0.5 microl, but not with the alpha2-adrenoceptors antagonist yohimbine 1.5 microg/0.5 microl. These results indicate that the N2O analgesic effect is mediated by activation of opiate receptors, but not alpha2-adrenoceptors, in the periaqueductal gray. Combined with the previous experiments that the N2O analgesic effect is reversed by intrathecal injection of an alpha2-adrenoceptor antagonist but not by an opiate receptor antagonist, it seems likely that N2O causes activation of the opiate receptors in the periaqueductal gray, which in turn activate the noradrenergic descending pathways to the spinal cord to produce the analgesic effect.
-
Randomized Controlled Trial Clinical Trial
Opioid-induced delay in gastric emptying: a peripheral mechanism in humans.
Opioids delay gastric emptying, which in turn may increase the risk of vomiting and pulmonary aspiration. Naloxone reverses this opiate action on gastric emptying, but it is not known whether this effect in humans is mediated by central or peripheral opiate antagonism. The importance of peripheral opioid receptor antagonism in modulating opioid-induced delay in gastric emptying was evaluated using methylnaltrexone, a quaternary derivative of the opiate antagonist naltrexone, which does not cross the blood-brain barrier. ⋯ The attenuation of morphine-induced delay in gastric emptying by methylnaltrexone suggests that the opioid effect is mediated outside the central nervous system. Methylnaltrexone may have the potential to decrease the side effects of opioid medications, which are mediated peripherally, while maintaining the central analgesia effect of the opioid.
-
Randomized Controlled Trial Comparative Study Clinical Trial
Oral naltrexone treatment for cholestatic pruritus: a double-blind, placebo-controlled study.
The efficacy of currently available therapeutic agents for cholestatic pruritus is often disappointing. The aim of this study was to assess the antipruritic effect of naltrexone, an oral opiate receptor antagonist. ⋯ For patients with cholestatic liver disease and itching, refractory to regular antipruritic therapy, oral naltrexone may be an effective and well-tolerated alternative.