Substance Misuse - Prescribing methadone for opioid addiction

Dr Carsten Grimm says controlled use of this potentially dangerous substance can be beneficial and dispels some myths about methadone.

The Standard concentration of methadone is 1mg/ml oral solution
The Standard concentration of methadone is 1mg/ml oral solution

Opioids, such as methadone and diamorphine, have a reputation as 'bad' drugs. Some consider them dangerous and addictive, and only to be used if there is no alternative.

It is true that prescribing opioids can be dangerous, but dosage is really the main pitfall, as the side-effects and interactions are similar for all opioids.

Pharmacologists often discriminate between different opioids based on the brain receptors they target, but this is not relevant in practice. The common effects of opioids are discussed further below.

Pain control
Opioids are very good painkillers and work well in controlling both chronic and acute pain.

Depending on the level and nature of pain, different preparations can be used, ranging from short-acting, low potency opioids, such as codeine to more potent ones like diamorphine. Further pain relief can be provided by long-acting opioids, such as methadone and buprenorphine.

This is the main reason opioids are misused; they create a 'high'. Patients describe feeling happy, relaxed and detached from reality.

Drowsiness and respiratory depression

Higher doses of opioids can make patients fall asleep and reduce respiratory drive, which can result in airway obstruction and death. Overdoses can be treated by either reducing the dose of prescribed opioid or, if necessary, by giving naltrexone.

This occurs when opioids are given rapidly for acute pain. It can be relieved by an antiemetic such as cyclizine.

This is a common side-effect of all opioids; loperamide, which is widely used to control diarrhoea, is nothing but an opioid that does not cross the blood-brain barrier. Constipation can be treated with laxatives like lactulose.

Addiction and withdrawal
Any opioid given over a long period of time can create a physical and psychological addiction. The longer the drug is prescribed and the higher the potency used, the more likely it is to become addictive.

However, in some situations, development of addiction is irrelevant, for example, in palliative care.

It is important to remember that withdrawal of opioids is not dangerous, but it can be very unpleasant.

Why is methadone prescribed?
The idea behind prescribing methadone for opioid misusers is simply to reduce harm. Heroin has a much shorter half-life than methadone and has to be taken several times a day to achieve a steady blood concentration.

Withdrawal sensations occur when blood levels start to drop. Methadone prevents this from happening by stabilising blood concentration. By creating a steady level, methadone also decreases the risk of overdose, resulting in fewer deaths.

Methadone can be given safely as a long-acting painkiller to replace other, shorter acting opioids, or as maintenance treatment in opioid misuse.

Methadone is typically taken once daily. The standard concentration is 1mg/ml oral solution; higher concentrations are available but rarely used. A typical maintenance dose is in between 30ml and 120ml daily.

Common myths

  • Methadone affects bones and teeth.

Methadone does not accumulate in bones and it does not ruin teeth. However, the sugar used in the liquid to counter the bitter taste might do this.

  • Methadone is a potent painkiller so someone taking it does not require additional analgesia.

Methadone is indeed a potent painkiller, but if it is prescribed for opioid misuse it does not raise pain tolerance, therefore patients do need additional analgesia, and often more to get the same effect as someone who is opioid-naive.

To give an example, someone on a stable dose of methadone who breaks their leg will need more morphine than someone not on methadone; the exact amount is a clinical decision and needs close supervision and assessment. Any opioid can be used on top of methadone apart from buprenorphine.

  • Methadone is more addictive than heroin.

It is difficult to rate the addictiveness of methadone or any drug. Heroin is often consumed via inhalation or injection, and the rapid rise in blood level is possibly responsible for its euphoric effects.

Methadone works slowly on the same brain receptors, and although patients report a sedating effect, it does not have the same potency as heroin.

  • Withdrawing from methadone is worse than from heroin.

There is some truth to this: the higher the dose of methadone taken, the worse is the withdrawal when it is stopped.

However, the symptoms of withdrawal from either drug are the same: sweating, tachycardia, nausea and vomiting, sleeplessness and a plethora of other symptoms. Clinically, it does not appear much worse than a flu-like illness and patients are never in danger from opioid withdrawal.

  • Methadone kills as many people as heroin.

This was true when methadone was first prescribed 30 years ago, but is not the case any more.

Patients were given methadone unsupervised, leading to uncontrolled consumption. These days, the starting dose should not exceed 30mg. Following review, the dose can be increased by a maximum of 10mg a day until withdrawal symptoms have ceased.

Higher doses of methadone (above 60mg) have been shown to be more effective at stopping heroin use in the long term.

  • Dr Grimm is a GP in West Yorkshire, GPSI in substance misuse and clinical lead for the RCGP alcohol certificate.

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