|Systematic (IUPAC) name|
|Trade names||Logicin and many others|
|Bioavailability||Maximum plasma conc. attained 4-8 hours after oral dose.|
|Half-life||32-43 hours; volume of distribution is 36-49L/kg.|
|Molecular mass||398.55 g/mol|
|(what is this?)|
Pholcodine is a drug which is an opioid cough suppressant (antitussive). It helps suppress unproductive coughs and also has a mild sedative effect, but has little or no analgesic effects. It is also known as morpholinylethylmorphine and homocodeine.
Pholcodine is found in certain cough lozenges. However, in the UK, the preparation is almost exclusively an oral solution, typically 5 mg / 5 ml. Adult dosage is 5-10ml up to 3-4 times daily. Pholcodine now largely replaces the previously more common codeine linctus, as it has a much lower potential for dependence.
Pholcodine is not prescribed in the United States where it is a Schedule I drug. It is a class B substance in the United Kingdom but can be purchased over-the-counter in most UK pharmacies.
Mechanism of action
Pholcodine is readily absorbed from the gastrointestinal tract and freely crosses the blood–brain barrier. It acts primarily on the central nervous system (CNS), causing depression of the cough reflex, partly by a direct effect on the cough centre in the medulla. It is metabolized in the liver and its action may be prolonged in individuals with hepatic insufficiency (i.e. liver problems). Its use is therefore contraindicated in patients with liver disease, while care is advised in patients with hepatic impairment.
Metabolism and excretion
Pholcodine is slowly biotransformed in the body via oxidation and conjugation to a series of metabolites that are eliminated primarily in the urine. With an average half-life of approximately 2.3 days, steady-state in someone taking the drug chronically would not be reached for nearly 2 weeks. Nearly one-half of a single dose is eventually excreted as free or conjugated parent drug. The most important urinary metabolite is conjugated morphine, which may be detectable for days or weeks after the last dose. This could trigger a positive result for opiates in a urine drug testing program.
Side effects are rare and may include dizziness and gastrointestinal disturbances such as nausea or vomiting. Adverse effects such as constipation, drowsiness, excitation, ataxia and respiratory depression have been reported occasionally or after large doses. The primary safety concerns with pholcodine revolve around death during general anaesthesia.
Anaphylaxis During General Anaesthesia
Administration of pholcodine causes production of antibodies linked with fatalities during surgery, when essential neuromuscular blocking agents (NMBAs) are administered to prevent patient movement under general anaesthesia. These antibody levels gradually fall to low levels several years after last dose of pholcodine. However, the presence of these antibodies causes a 300-fold increase in risk of anaphylaxis during anaesthesia.
The link was suspected when neighbouring Norway and Sweden were found to have tenfold differences of surgical anaphylaxis deaths. Sweden had no products approved containing pholcodine, whereas 40% of the population in Norway had consumed the single approved pholcodine product. Norway withdrew pholcodine from the market in 2007, and the prevalence of anti-suxamethonium antibodies fell by over 80% in two years. A corresponding fall in anaesthesia deaths followed.
A similar disparity exists between NMBA anaphylaxis rates in Australia, where pholcodine consumption is high and the US, where pholcodine is banned. In the US, anaphylaxis rates are so low that some anaesthetists question the existence of such reactions to NMBAs. Conversely, Australian anaesthetists have requested a ban on pholcodine due to the high anaphylaxis rate in the country. However, the Therapeutic Goods Administration declined the request in January 2015, pending further reviews to follow.
- BNF (2007). British National Formulary 54. BMJ Publishing Group Ltd., RPS Publishing, London. Page 175.
- US Food and Drug Administration. (2009) "Legislation - Controlled Substances" http://www.fda.gov/RegulatoryInformation/Legislation/ucm148726.htm
- Maurer, Hans H.; Fritz, Christian F. (1990). "Toxicological detection of pholcodine and its metabolites in urine and hair using radio immunoassay, fluorescence polarisation immunoassay, enzyme immunoassay and gas chromatography-mass spectrometry". International Journal of Legal Medicine 104 (1): 43–6. doi:10.1007/BF01816483. PMID 11453092.
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- Sadleir, P. H. M.; Clarke, R. C.; Bunning, D. L.; Platt, P. R. (2013). "Anaphylaxis to neuromuscular blocking drugs: Incidence and cross-reactivity in Western Australia from 2002 to 2011". British Journal of Anaesthesia 110 (6): 981. doi:10.1093/bja/aes506. PMID 23335568.
- Levy, Jerrold H. (2004). "Anaphylactic Reactions to Neuromuscular Blocking Drugs: Are We Making the Correct Diagnosis?". Anesthesia & Analgesia: 881. doi:10.1213/01.ANE.0000115146.70209.4B.
- Crilly, Helen; Rose, Michael (2014). "Anaphylaxis and anaesthesia–can treating a cough kill?". Australian Prescriber: 74.
- Katelaris, Constance H.; Kurosawa, Motohiro; Moon, Hee-Bom; Borres, Magnus; Florvaag, Erik; Johansson, Stig Gunnar Olof (2014). "Pholcodine consumption and immunoglobulin E-sensitization in atopics from Australia, Korea, and Japan". Asia Pacific Allergy 4 (2): 86. doi:10.5415/apallergy.2014.4.2.86. PMID 24809013.
- "Cough medicine alert over surgery ", The Age, January 5, 2015. http://www.theage.com.au/national/health/cough-medicine-alert-over-surgery-20150105-12i8sq.html
- Australian Therapeutic Goods Admission document on Pholcodine (Rich Text Format)