VETcpd - Pharmacology Peer Reviewed Drug Focus: Tramadol … · 2019-05-20 · Tramadol undergoes...
Transcript of VETcpd - Pharmacology Peer Reviewed Drug Focus: Tramadol … · 2019-05-20 · Tramadol undergoes...
Page 54 - VETcpd - Vol 1 - Issue 4
Drug Focus:Tramadol Hydrochloride
BackgroundTramadol hydrochloride is a synthetic product similar to codeine, licensed for use as an analgesic in humans for moderate to severe pain, including post-operative pain. WHO, the World Health Organisation, classifies it on their ‘analgesic ladder’ as sit-ting between the relatively weak NSAIDs (non-steroidal anti-inflammatory drugs) and the relatively strong morphine type opioids. In humans it is generally consid-ered effective, safe and well tolerated.
It is now listed (since June 2014) as a Schedule 3 Controlled Drug, under the Misuse of Drugs regulations 2001. Tramadol is exempt from Safe Custody regulations, however the RCVS advises that all Schedule 3 drugs are locked away. Although it does not need to be recorded in the Controlled Drugs Register, it is sub-ject to special prescription requirements. For further information go to www.bsava.com/Resources/BSAVAMedicinesGuide/ControlledDrugs.aspx
Currently tramadol is not licensed in any veterinary species, however it has become increasingly popular as an analgesic adjunct in canine (and feline) patients over the past few years. Unfortunately there is very little safety or efficacy data published in these species and most of the information available is anecdotal. Oral and injectable formulations are available.
Debbie Doyle MA VetMB MRCVSDebbie spent 5 years in general practice before going into industry and specialising in the area of pain management. She published a text book on the subject in 2006, commissioned by Elsevier Ltd.
From 2004 to 2007 Debbie was elected Secretary of the British Veterinary Orthopaedic Association and currently works as a free-lance veterinary writer.
E-mail: [email protected]
Tramadol hydrochloride is not licensed in any veterinary species. Therefore it should only be used according to the Prescribing Cascade. For further guidance go to: www.vmd.defra.gov.uk/pdf/vmgn/VMGNote13.pdf
The majority of information available about the safety and efficacy of tramadol in dogs and cats is anecdotal
60% of tramadol activity is due to serotonin and noradrenalin reuptake inhibition40% of tramadol activity is due to mu-opioid receptor agonism
Mode of Action (Fox 2010)Tramadol is a centrally acting analge-sic with both opioid and non-opioid mechanisms of action. The drug comprises of two independently acting enantiom-ers, both of which are required for full analgesic activity: • R-enantiomer - inhibits noradrenalin
reuptake, which provides 40% of the drug’s overall analgesic effect.
• S-enantiomer - acts as both a mu opioid receptor agonist and a serotonin (5-HT) reuptake inhibitor, producing 40% and 20% respectively of the drugs overall analgesic effect.
The combination of the two enantiom-ers is synergistic, i.e. they produce a greater effect than the additive effect of each enantiomer used alone. There is no evidence of any COX (cyclo-oxygenase) inhibition by tramadol.
Interestingly, a study in human patients with knee osteoarthritis demonstrated that both tramadol and its active metabo-lite penetrate into joint fluid, significantly reducing synovial fluid levels of sub-stance P (Bianchi, Broggini, Balzarini et al 2003). Substance P is involved in potentiating nociceptive signals arising from inflamed joints. The study found not only did tramadol significantly reduce the intensity of joint pain, but the data also suggested that the activity of tramadol might also involve the modula-tion of inflammatory mediators (Bianchi, Broggini, Balzarini et al. 2003).
MetabolismTramadol undergoes extensive hepatic metabolism and the metabolites produced are hugely variable between individuals. At least 32 different metabolites have been identified in dogs (Fox 2010). Laboratory studies (Fox 2014), demonstrated that approximately 16% of tramadol is demeth-ylated to O-desmethyl-tramadol (M1 demethylated metabolite) in dogs, which appears to have a much greater binding affinity for mu-opioid receptors than the parent drug. Therefore it’s likely the metabolite is providing a significant anal-gesic effect. However, the M1 metabolite
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