Opioid analgesic
Opioid analgesics, also called narcotics, are drugs usually used for treating pain. Opiod analgesics are defined as "all of the natural and semisynthetic alkaloid derivatives from opium, their pharmacologically similar synthetic surrogates, as well as all other compounds whose opioid-like actions are blocked by the nonselective opioid receptor antagonist naloxone.[1]
Pharmacology
There a several opioid receptors. All are are G-protein-coupled cell surface receptors.
Clinically useful analgesic families vary in their receptor effects; they range from pure agonists of all receptor types, to selective agonists, to agonist-antagonists.
| Receptor | Functions |
|---|---|
| Delta | Analgesia, |
| Kappa | Analgesia, inhibition of gastrointestinal motility, psychotropic effect |
| Mu | Analgesia, inhibition of gastrointestinal motility, inhibition of respiration, sedation and physical dependency |
Available opioid analgesics
Current opioid analgesics are below[3] Tables of morphine equivalent daily dose and IV to PO conversion are available to help dosing.[3]
| Specific drug | Receptor action | Comments |
|---|---|---|
| Naturally occurring opium alkaloids | ||
| Morphine | mu, (kappa) | |
| Codeine | mu (partial agonist) | Good oral absorption |
| Semi-synthetic opioids | ||
| Diacetylmorphine (heroin) | Faster blood-brain transfer than morphine but both produce the same primary active metabolite | |
| Buprenorphine | mu, antagonist of delta and kappa | |
| Fully synthetic opioids | ||
| Fentanyl | mu | Transdermal and transmucosal absorption |
| Methadone | mu | Good oral absorption |
| Tramadol | mu | also inhibits norepinephrine reuptake |
Effectiveness
Narcotics are commonly prescribed for pain, and their usage may be increasing.[4] In emergency rooms, non-Hispanic white patients are more likely to receive narcotics than patients of other ethnicities.[4]
Narcotics are effective for both short (1-16 weeks)[5] and long-term (6-24 months) use[6].
Narcotics, with long-term use, 80% of patients may have drug toxicity, most commonly gastrointestinal. In addition, substrance abuse and "aberrant medication-taking behaviors" may occur.[7] Advice for using administering chronic narcotics[8] and for treating acute pain among patients on chronic methadone is available[9].
Usage
Clinical practice guidelines are available.[8]
Tables of morphine equivalent daily dose and IV to PO conversion are available to help dosing.[3]
Adverse effects
Constipation
Constipation may be reduced by methylnaltrexone, a mu-opioid receptor antagonist. In a randomized controlled trial, 48% of patients receiving methylnaltrexone had a bowel movement compared to 15% of patients received placebo (number needed to treat = 3.0. Click here to adjust these results for patients at higher or lower risk.)[10] Although mu-receptors provide analgesia, methylnaltrexone is a charged quaternary amine so that it does not well cross the blood-brain barrier.
Dependency
Substance abuse
With chronic use for treatment of pain, dependency may lead to substance abuse and "aberrant medication-taking behaviors" may occur.[7]
Withdrawal
Adding narcotic antagonists combined with alpha-adrenergic agonists may reduce withdrawal symptoms.[11]
Tolerance
N-methyl-d-aspartate receptor (NMDA) activation may lead to neuropathic pain and tolerance.[12][13] Methadone, which is a NMDA antagonist, may reduce tolerance.
References
- ↑ Katzung, Bertram G. (2006). Basic and clinical pharmacology. New York: McGraw-Hill Medical Publishing Division, 512. ISBN 0-07-145153-6.
- ↑ 2.0 2.1 Masters, Susan B.; Katzung, Bertram G.; Trevor, Anthony J. (2009). “Basic Pharmacology of the Opioid Analgesics”, Basic and Clinical Pharmacology, 11th. New York: McGraw-Hill Medical. ISBN 0-07-160405-7. Cite error: Invalid
<ref>tag; name "isbn0-07-160405-7-=Basic Pharmacology of the Opioid Analgesics" defined multiple times with different content - ↑ 3.0 3.1 3.2 (2003) “78. Management of Cancer Pain”, Cancer medicine 6. Hamilton, Ont.: BC Decker. ISBN 1-55009-213-8.
- ↑ 4.0 4.1 Pletcher MJ, Kertesz SG, Kohn MA, Gonzales R (2008). "Trends in opioid prescribing by race/ethnicity for patients seeking care in US emergency departments". JAMA 299 (1): 70–8. DOI:10.1001/jama.2007.64. PMID 18167408. Research Blogging.
- ↑ Furlan AD, Sandoval JA, Mailis-Gagnon A, Tunks E (2006). "Opioids for chronic noncancer pain: a meta-analysis of effectiveness and side effects". CMAJ 174 (11): 1589–94. DOI:10.1503/cmaj.051528. PMID 16717269. Research Blogging.
- ↑ Kalso E, Edwards JE, Moore RA, McQuay HJ (2004). "Opioids in chronic non-cancer pain: systematic review of efficacy and safety". Pain 112 (3): 372–80. DOI:10.1016/j.pain.2004.09.019. PMID 15561393. Research Blogging.
- ↑ 7.0 7.1 Martell BA, O'Connor PG, Kerns RD, et al (2007). "Systematic review: opioid treatment for chronic back pain: prevalence, efficacy, and association with addiction". Ann. Intern. Med. 146 (2): 116–27. PMID 17227935. [e]
- ↑ 8.0 8.1 Chou R, Fanciullo GJ, Fine PG, Adler JA, Ballantyne JC, Davies P et al. (2009). "Clinical guidelines for the use of chronic opioid therapy in chronic noncancer pain.". J Pain 10 (2): 113-30. DOI:10.1016/j.jpain.2008.10.008. PMID 19187889. Research Blogging.
- ↑ Alford DP, Compton P, Samet JH (2006). "Acute pain management for patients receiving maintenance methadone or buprenorphine therapy". Ann. Intern. Med. 144 (2): 127–34. PMID 16418412. [e]
- ↑ Thomas J, Karver S, Cooney GA, Chamberlain BH, Watt CK, Slatkin NE, Stambler N, Kremer AB, Israel RJ. Methylnaltrexone for opioid-induced constipation in advanced illness. N Engl J Med. 2008 May 29;358(22):2332-43. PMID 18509120
- ↑ Gowing L, Ali R, White JM (2009). "Opioid antagonists with minimal sedation for opioid withdrawal.". Cochrane Database Syst Rev (4): CD002021. DOI:10.1002/14651858.CD002021.pub3. PMID 19821290. Research Blogging.
- ↑ Trujillo KA, Akil H (1991). "Inhibition of morphine tolerance and dependence by the NMDA receptor antagonist MK-801.". Science 251 (4989): 85-7. PMID 1824728.
- ↑ Prommer E (2006). "Rotating methadone to other opioids: a lesson in the mechanisms of opioid tolerance and opioid-induced pain.". J Palliat Med 9 (2): 488-93. DOI:10.1089/jpm.2006.9.488. PMID 16629581. Research Blogging.