Opioid poisoning/overdose

It is inactive orally because of high first pass metabolism in liver. Metabolised by glucuronidation in liver. The main use of naloxone is in the treatment of acute opioid overdose (acute morphine poisoning). It also precipitates withdrawal syndrome when administered to morphine addicts. The constricted pupils of addicts dilate after administration of naloxone. This has been used as a diagnostic tool for opioid addiction. 

The major application of naloxone is in the treatment of acute opioid overdose (see also Chapter 59 Management of the Poisoned Patient). It is very important that the relatively short duration of action of naloxone be borne in mind, because a severely depressed patient may recover after a single dose of naloxone and appear normal, only to relapse into coma after 12 hours. 

Although methadone is used for the management of opioid dependence, symptoms of overdose are similar to those of morphine poisoning. 

Action on receptors provides numerous examples. Beneficial interactions are sought in overdose, as with the use of naloxone for morphine overdose (opioid receptor), of atropine for anticholinesterase, i.e. insecticide poisoning (acetylcholine receptor), of isoproterelol (isoprenaline) for overdose with a P-adrenoceptor blocker (p-adrenoceptor), of phentolamine for the monoamine oxidase inhibitor-sympathomimetic interaction (a-adrenoceptor). 

Propoxyphene is an agonist of opioid fi receptors. It is this opioid effect that is responsible for the central nervous system and respiratory depression seen in overdose. Both propoxyphene and norpropoxyphene are potent blockers of myocardial sodium channels, an effect identical to type lA antidysrhythmic agents. This myocardial sodium channel blockade may result in prolongation of the electrocardiogram QRS complex, arrhythmias, and cardiovascular depression seen in propoxyphene poisoning. 

IV. Diagnosis. Poisoning should be suspected in patients with pinpoint pupils, respiratory depression, hypotension, and bradycardia. Although clonidine overdose may mimic an opioid overdose, it does not usually respond to administration of... 

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