Agonist & antagonist substitution

• What is an example of an agonist drug?

  Methadone-treats opioid addictions & is produced synthetically to mimic some effects of heroin. Part of maintenance treatment. Reduces cravings & prevents withdrawal symptoms.
• What is agonist substitution?

  Chemical binds to postsynaptic receptor & activates receptor to produce response. Imitate action of another substance, e.g, heroin.
• What is antagonist substitution?

  Antagonist binds to receptor- doesn't cause reaction; blocks usual function of particular substance.
• What is an example of an antagonist drug?

  Naltrexone-primarily used in abstinence stage of recovery from addiction. Blocks euphoric & pleasurable effects from opioids & makes them less rewarding.
• NICE guidelines UK (naltrexone) :


  Should be used by people who have stopped opioids. Oral medication, implant or depot injection (medication injected but released slowly over period of weeks). Alcohol addiction alongside psychological intervention & should be used after withdrawal of alcohol. Can be used for up to 6-month period & kept under supervision to check they haven't drunk again.
• NICE guidelines UK (methadone) :

  Suggest initial dose of 10-40mg each day, which is increased by up to 10mg daily until no signs of withdrawal or intoxication seen. Individual reaches a maintenance dose of 60-120mg a day. Usually given orally as a green liquid-available as tablet or injection. Orally avoids risks with needle use & injections.
• How is methadone use supervised?

  Dr sees patients each day first 3 months until able to continue without supervision. Helps ensure dosage is right & people don't take multiple doses at once or sell methadone. Recommended alongside other psychosocial support. Dosage reduced over time (detoxification) until individual stops using it completely (abstinence).
• Gyngell (2011) :


  Report by centre for policy studies said prescribing methadone was 'expensive failure' & costs society money, not only for methadone but for 320,000 problem drug users on benefits. Greater success would be achieved by funding rehabilitation units encouraging abstinence.
• Doward (2011) :


  Charity DrugScope disputed claims in report saying it overestimated cost of prescribing methadone. Also highlighted that National Audit office had described drug treatment as good value for money for taxpayer, as many people on methadone become able to function in society as result of making their addiction manageable.
• Gyngell (2011) :


  Centre for policy studies report claimed drug-related reoffending has continued to rise despite availability of drug treatments like methadone.
• Report by National Treatment Agency (2009) :


  Treating heroin users with methadone has immediate positive effect on society by reducing their criminality. Suggest rates of offending are reduced by half when addicts are in treatment.
• Setting up methadone programmes centred on a particular area, groups of addicts are convening in a particular place- people concerned about possible increases in crime & antisocial behaviour in neighbourhood.
• Boyd et al (2012) :


  Researched treatment centres in Baltimore & found crime rates around them were similar to the surrounding areas.
• What are the side effects of naltrexone?

  Greater risk of overdose-if individual chooses to return to taking a drug they'll need more of it to feel same effects & are therefore more likely to overdose. Carefully monitored for issues with liver function & if they're still opioid dependent it can cause withdrawal symptoms as naltrexone can displace opioids still in system from their receptors.
• What are the ethical issues with methadone?

  Methadone may interact with other drugs (e.g, alcohol & antidepressants) to cause respiratory problems. Danger of overdose if an addict combines methadone with other drugs. Office for National statistics reported in 2013, methadone was responsible for 429 deaths in UK. Creates another addiction-many remain on methadone for prolonged periods of time & without right support will struggle to make it to detoxification & abstinence stage.
• Van den Brink & Haasen (2006) :


  1 meta-analysis of studies into effectiveness of a range of treatments concluded that as long as dosage is adequate then methadone is effective as a maintenance treatment.
• Effectiveness of methadone (NICE) :

  Assessed 31 reviews of its effectiveness, including 27 randomised controlled trials. Found higher levels of retention for people using methadone than placebo or no treatment & lower rates of illicit opioid use.
• Lahti et al (2010) :


  Tested effectiveness of naltrexone on small sample of gamblers who were instructed to take it before gambling or when they felt urge to. Found significant decreases in gambling levels, although they highlight that further research is needed, e.g, with placebo for comparison.
• Effectiveness of naltrexone (NICE) :


  Reviewed 17 studies concerning effectiveness of naltrexone for heroin addiction. Found conflicting results overall, & many of the randomised controlled trials showed no significant difference between naltrexone & a control treatment for retention on the treatment programme. When results were pooled they found naltrexone was associated with reduction in relapse rates, particularly in those highly motivated, & where patients were closely monitored & offered extra support.
• What is buprenorphine?

  Alternative to methadone. Milder & has both agonist & antagonist properties. Activates opioid receptors to produce an opiate effect like methadone (agonist) but also blocks euphoria in similar way to naltrexone (antagonist). Less risk of overdose due to its 'ceiling effect' - after certain amount taken, taking anymore doesn't increase effects of drug.
• Marteau et al (2015) :


  Analysed data for a 5-year period & concluded that buprenorphine was 6 times safer than methadone. Methadone is preferred treatment option in UK- more effective in retaining patients in treatment, possibly as addict prefers feeling they get from methadone so more likely to continue treatment (Whelan & Remski, 2012).