Opioid analgesic

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Opioid analgesics, also called narcotics, are drugs usually used for treating pain. Opioid 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.

Opioid receptors[2]
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] although direct conversion is unwise with opioids with complex pharmacodynamics, such as methadone.

A number of oral forms are combined with acetaminophen to reduce the possibility of diversion to injected abuse, although acetaminophen also has a distinct and potentially synergistic analgesic effect. Acetaminophen has been found to be more toxic, with or without opioids, than had been generally believed, and the FDA has recommended restrictions on its uses.[4] The American Pain Foundation is concerned that these recommendations consider the matter carefully, lest there be undertreatment with appropriate opioids. [5]

Combination with aspirin and other non-narcotic agents was common before the widespread use of acetaminophen.


Selected opioids[2]
Specific drug Potency relative to morphine[6]0 Chemical class Receptor action Metabolism[7][8] Comments
Naturally occurring opium alkaloids
Morphine 1 morphine mu, kappa (weak)
Codeine 0.15 morphine mu (partial agonist) Good oral absorption
Semi-synthetic opioids
Diacetylmorphine (heroin) morphine Faster blood-brain transfer than morphine but both produce the same primary active metabolite
Hydrocodone and Oxycodone 1
1.5 		morphine mu (partial)
Hydromorphone (Dilaudid) 4 morphine mu Mostly hepatic Oral bioavailability is approximately 24%[9]
Buprenorphine Thebaine mu, antagonist of delta and kappa
Fully synthetic opioids
Meperidine 0.1 Meperidine mu Good oral absorption; toxic metabolite accumulates on prolonged use
Fentanyl 2.4 Meperidine mu Transdermal and transmucosal absorption
Methadone 3 methadone mu Good oral absorption. Bioavailability of methadone ranges between 36 to 100%.[10] Different half-lives for analgesia and for blocking withdrawal
Tramadol 0.1 codeine mu Also inhibits monoamine oxidase; can raise norepinephrine and serotonin, and cause serotonin syndrome
Propoxyphene 0.23 propoxyphene mu D-isomer is analgesic; L-isomer is antitussive

Effectiveness

Narcotics are commonly prescribed for pain, and their usage may be increasing.[11] In emergency rooms, non-Hispanic white patients are more likely to receive narcotics than patients of other ethnicities.[11]

Narcotics are effective for both short (1-16 weeks)[12] and long-term (6-24 months) use[13].

Usage

Clinical practice guidelines are available.[14]

Tables of morphine equivalent daily dose and IV to PO conversion are available to help dosing, but must be used with caution. Some opioids, such as methadone, do not lend themselves to simple conversion due to greatly differing half-lives. While an antagonist or partial antagonist may have equianalgesic dosing in an opioid-naive patient, switching from, for example, long-term morphine to buprenorphine can cause withdrawal.

Chronic use

Appropriate use may be improved with prescription-drug monitoring programs in which prescribers can track all opioid prescriptions for a patient. This has been studied for the Ohio Automated Rx Reporting System (OARRS).[15] Two additional systems under development are bu the United States Department of Health and Human Services and one by the Department of Justice.[16]

Advice for using administering chronic narcotics[14] and for treating acute pain among patients on chronic methadone is available[17].

Adverse effects

Narcotics, with long-term use, 80% of patients may have drug toxicity, most commonly gastrointestinal. In addition, substance abuse and "aberrant medication-taking behaviors" may occur.[18]

Serious drug toxicity from long-term use may be low according to one systematic review.[19]

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.)[20] Although mu-receptors provide analgesia, methylnaltrexone is a charged quaternary amine so that it does not well cross the blood-brain barrier.

Dietary agents and inert physical agents may help. A high-fiber diet is desirable, possibly with fiber supplements such as psyllium and metacellulose. The stool softener docusate is often prescribed. Stronger laxatives are not desirable.

Dependency

For more information, see: Opiate dependence.

Opioid agonist therapy includes buprenorphine and methadone. Although buprenorphine–naloxone may be less effective than methadone[21], it has more predictable dosing[22], and can be prescribed by qualifying office-based physicians.[23]

Overdose

Chronic use of the equivalent of more than 20 mg/day of morphine may lead to unintentional or intentional overdose.[24]

Substance abuse

With chronic use for treatment of pain, dependency may lead to substance abuse and "aberrant medication-taking behaviors" may occur.[18] Contracts may reduce abuse, but comparative studies provide conflicting results.[25] Most agreements stated, "patients agreed not to abuse illicit drugs or alcohol, obtain opioids from more than 1 provider or pharmacy, or request a refill before the previous prescription should have been completed."

Withdrawal

Adding narcotic antagonists combined with alpha-adrenergic agonists may reduce withdrawal symptoms.[26]

Tolerance

N-methyl-d-aspartate receptor (NMDA) activation may lead to neuropathic pain and tolerance.[27][28] Methadone, which is a NMDA antagonist, may reduce tolerance.

Pruritis

Pruritis from histamine release may occur.[29] Anecdotally, one of the reason for using antihistamines as adjuvants, such as hydroxyzine and promethazine, are to alleviate some of these side effects, as well as nausea. The less sedating hydroxyzine also may potentiate analgesia and have a better antipruritic effect although promethazine may be stronger against nausea.

References

  1. ↑ Katzung, Bertram G. (2006). Basic and clinical pharmacology. New York: McGraw-Hill Medical Publishing Division, 512. ISBN 0-07-145153-6. 
  2. ↑ 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. ↑ 3.0 3.1 (2003) “78. Management of Cancer Pain”, Cancer medicine 6. Hamilton, Ont.: BC Decker. ISBN 1-55009-213-8. 
  4. ↑ [http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterial/Drug/DrugSafetyandRiskManagementAdvisoryCommittee/UCM170188.pdf Joint Meeting of the Drug Safety and Risk Management Advisory Committee, Nonprescription Drugs Advisory Committee, and the Anesthetic and Life Support Drugs Advisory Committee], Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA), June 29-30, 2009
  5. ↑ American Pain Foundation shares Acetaminophen Task Force's Concerns over Recent FDA Advisory Committee Recommendations Regarding Prescription Acetamenophen/Opioid Combination, American Pain Foundation
  6. ↑ Korff MV, Saunders K, Thomas Ray G, Boudreau D, Campbell C, Merrill J et al. (2008). "De facto long-term opioid therapy for noncancer pain.". Clin J Pain 24 (6): 521-7. DOI:10.1097/AJP.0b013e318169d03b. PMID 18574361. Research Blogging.
  7. ↑ Davies G, Kingswood C, Street M (1996). "Pharmacokinetics of opioids in renal dysfunction.". Clin Pharmacokinet 31 (6): 410-22. PMID 8968655.
  8. ↑ Conway BR, Fogarty DG, Nelson WE, Doherty CC (2006). "Opiate toxicity in patients with renal failure.". BMJ 332 (7537): 345-6. DOI:10.1136/bmj.332.7537.345. PMID 16470057. PMC PMC1363915. Research Blogging.
  9. ↑ Hydromorphone - FDA approved drug information (drug label) from DailyMed (U.S. National Library of Medicine).
  10. ↑ Methadone - FDA approved drug information (drug label) from DailyMed (U.S. National Library of Medicine).
  11. ↑ 11.0 11.1 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.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ 14.0 14.1 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.
  15. ↑ Baehren DF, Marco CA, Droz DE, Sinha S, Callan EM, Akpunonu P (2010). "A statewide prescription monitoring program affects emergency department prescribing behaviors.". Ann Emerg Med 56 (1): 19-23.e1-3. DOI:10.1016/j.annemergmed.2009.12.011. PMID 20045578. Research Blogging.
  16. ↑ McLellan AT, Turner BJ (2010). "Chronic noncancer pain management and opioid overdose: time to change prescribing practices.". Ann Intern Med 152 (2): 123-4. DOI:10.1059/0003-4819-152-2-201001190-00012. PMID 20083830. Research Blogging.
  17. ↑ 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]
  18. ↑ 18.0 18.1 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]
  19. ↑ Noble M, Treadwell JR, Tregear SJ, Coates VH, Wiffen PJ, Akafomo C et al. (2010). "Long-term opioid management for chronic noncancer pain.". Cochrane Database Syst Rev (1): CD006605. DOI:10.1002/14651858.CD006605.pub2. PMID 20091598. Research Blogging.
  20. ↑ 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
  21. ↑ Schottenfeld RS, Chawarski MC, Pakes JR, Pantalon MV, Carroll KM, Kosten TR (2005). "Methadone versus buprenorphine with contingency management or performance feedback for cocaine and opioid dependence.". Am J Psychiatry 162 (2): 340-9. DOI:10.1176/appi.ajp.162.2.340. PMID 15677600. Research Blogging. Review in: Evid Based Ment Health. 2005 Nov;8(4):112>
  22. ↑ Simoens S, Matheson C, Bond C, Inkster K, Ludbrook A (2005). "The effectiveness of community maintenance with methadone or buprenorphine for treating opiate dependence.". Br J Gen Pract 55 (511): 139-46. PMID 15720937. PMC PMC1463190.
  23. ↑ Sullivan LE, Fiellin DA (2008). "Narrative review: buprenorphine for opioid-dependent patients in office practice.". Ann Intern Med 148 (9): 662-70. PMID 18458279.
  24. ↑ Dunn KM, Saunders KW, Rutter CM, Banta-Green CJ, Merrill JO, Sullivan MD et al. (2010). "Opioid prescriptions for chronic pain and overdose: a cohort study.". Ann Intern Med 152 (2): 85-92. DOI:10.1059/0003-4819-152-2-201001190-00006. PMID 20083827. Research Blogging.
  25. ↑ Starrels, Joanna L.; William C. Becker, Daniel P. Alford, Alok Kapoor, Arthur Robinson Williams, Barbara J. Turner (2010-06-01). "Systematic Review: Treatment Agreements and Urine Drug Testing to Reduce Opioid Misuse in Patients With Chronic Pain". Annals of Internal Medicine 152 (11): 712-720. DOI:10.1059/0003-4819-152-11-201006010-00004. Retrieved on 2010-06-01. Research Blogging.
  26. ↑ 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.
  27. ↑ 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.
  28. ↑ 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.
  29. ↑ Cherny N, Ripamonti C, Pereira J, Davis C, Fallon M, McQuay H et al. (2001). "Strategies to manage the adverse effects of oral morphine: an evidence-based report.". J Clin Oncol 19 (9): 2542-54. PMID 11331334.
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