Regarding naloxone/naltrexone. I am not sure if my understanding is correct...is it correct that naloxone or naltrexone is used for opiod overdose but methadone for withdrawal? So basically, do you only use methadone for opiod toxicitiy if the pt is experieincing withdrawals and in all other cases use naloxone? I just can't quite understand when to use one or the other.
Also for alcohol overdose, do you only use benzo's for DT's and then naloxone for overdose without withdrawal symptoms? I hope this questions makes sense...
Just remember two simple rules first:
1. In acute overdose/toxicity, you want to antagonize/block the poison that is in the system.
2. To prevent or treat withdrawal, you want to provide something that acts very much like the poison the system is used to (tincture of opium anyone?).
Next, remember the rule that rapid onset and short half life drugs have rapid onset of severe withdrawal symptoms. Long half life drugs have less severe withdrawal profiles. So if you have to give something to treat withdrawal, try to substitute their "quick" high for one that is less intense and longer lasting, so that when they do stop that "maintenance" drug it is less severe.
Now take the opioid case first, and apply those rules:
1. In acute OD, provide an opioid antagonist. Naloxone and Naltrexone fit that bill. They block opioid receptors.
2. To treat/prevent/slow withdrawals, provide something similar to what they are used to. Methadone is a long acting opioid, so it works well. Less intense high, longer lasting, less severe withdrawal, so it is easy to make the transition to being on nothing.
Now take the alcohol case:
1. In acute alcohol overdose, you would like to provide an alcohol antagonist, but there really isn't one. The closest thing is fomepizole, which blocks the conversion of alcohol to the metabolite that does long term damage - acetaldehyde. But in the short term it is the EtOH that is doing the damage, and you don't want to block its metabolism. There isn't anything I know of that antagonizes EtOH's effects to any great degree. I've never heard about naltrexone having that effect. So you provide supportive care... glucose and thiamine, respiratory support if needed.
2. In alcohol withdrawal, provide something similar to what they are used to. EtOH and benzodiazapines are both sedative/hypnotics, cross-react with one another, and are perceived by the body in much the same way. Diazepam and chlordiazepoxide are both long acting benzo's that can be substituted for alcohol. It is then easier to taper the benzo to abstinence than it would be for alcohol.
Alcohol is also interesting in that you can also give disulfiram, which blocks the further conversion of acetaldehyde to acetic acid. Acetaldehyde irritates the body and causes bad hangovers, so by putting someone on a prescription of disulfiram you just ensure that if they
do drink they seriously regret it the next day.
Note that in ethylene glycol and methanol ingestion, it is the metabolites that do the most damage, not the ethylene glycol or methanol. So you give fomepizole, which blocks their metabolism until they can be cleared safely from the system. If you don't have any handy (and maybe if you do?) you can also give them ethanol, which plays the role of competitive antagonist at the enzyme doing the metabolism (the one fomepizole blocks - alcohol dehydrogenase).
