Aug 29, 2011: If suboxone has naloxone in it, why do patients develop opioid toxicity when they ingest suboxone?

Suboxone is a relatively new treatment strategy for opioid addition and is a combination of buprenorphine and naloxone. Buprenorphine is a semi-synthetic opioid with partial agonist effects and is able to compete with other opioids for binding to the Mu receptor since it has a slow dissociation time from the receptor. It is well absorbed sublingually and less well absorbed orally.  Buprenorphine is metabolized to one active metabolite and several inactive metabolites. The active metabolite can cause respiratory depression like the parent compound.

Buprenorphine alone has been approved by the FDA with the trade name of subutex. Suboxone is buprenorphine with naloxone. The intent of combining the naloxone with the buprenorphine is to reduce the likelihood of a patient dissolving the buprenorphine into solution and injecting it. Intravenous administration of buprenorphine would increase its bioavailability and its associated, desired central opioid effects.

 So why doesn’t the naloxone block the effects of burprenorphine when taken the way it was intended (orally or sublingually)? Naloxone has very poor bioavailability when given by any other route other than intravenously. In other words, naloxone doesn’t really work when taken by mouth. Thus for the opioid addict, suboxone provides the buprenorphine but deters the likelihood of intravenous abuse of the drug. However, for the child with unintentional ingestion (or the drug addict who doesn’t understand the pharmacology), the oral naloxone does not reverse the acute toxicity of opioid poisoning. So these patients require intravenous dosing of naloxone to keep them breathing. High doses of IV naloxone may be required since buprenorphine is a good competitor at the Mu receptor site and has an active metabolite.


This question prepared by: Saralyn Williams, MD   Medical Toxicologist


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Donna Seger, MD

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