Drugs Used in the Treatment of Opioid Dependence
Opioid-dependent patients must receive opioids to prevent withdrawal while in hospital (see Withdrawal Prevention Algorithm ) and may require higher doses of opioids to produce analgesia (see Analgesia in Patients with Opioid Dependence), owing to opioid tolerance.
Opioid substitution therapy involves providing controlled doses of long-acting opioids to maintain blood levels within a narrow range, such that patients experience minimal intoxication and minimal withdrawal, thus reducing the sensations driving opioid drug seeking and drug misuse.
Methadone is the first line prescribed treatment for opioid dependence (NICE 2015) and the most appropriate opioid to prevent withdrawal as it has a long half-life, controls addictive behaviour, reduces drug hunger and is less likely to produce euphoria than other opioids.
On Methadone maintenance treatment (MMT)
Methadone is a long-acting opioid agonist which reduces addictive behaviour. It induces opioid tolerance which then makes pain management in these patients difficult as they require higher doses of opioid to provide analgesia. It is important to understand that the patient will not gain any meaningful analgesia from the methadone, and that withdrawal prevention and analgesia provision should be treated as separate entities.
If the maintenance methadone dose is known (and confirmed with the GP and pharmacy) and has been reliably taken for the past 3 days, it is safe to continue that dose while in hospital, either as a single dose or in two or three divided doses.
However, methadone can cause prolongation of the corrected electrocardiographic QT interval, which may predispose patients to the ventricular arrhythmia torsades de pointes. Acute illness and co-prescription of acute medicines may increase the risk of cardiac arrhythmia in hospital in patients who may have previously been stable. Circumstances include electrolyte abnormalities such as hypokalaemia or hypomagnesaemia; impaired liver function; and the use of drugs with QT–prolonging properties, for example antibiotics and benzodiazepines.
If the methadone dose is not certain and cannot easily be confirmed (e.g. over a weekend), or if there is doubt as to whether the patient has been taking that dose, then there is a risk of overdose. In this case the patient should be started on a methadone dose of up to 20mg as recommended in the withdrawal prevention algorithm ( Withdrawal Prevention Algorithm) and given more later as necessary according to the COWS ( Clinical Opioid Withdrawal Scale (COWS)) assessment. No patient should ever be given a dose of methadone if there is a suspicion of intoxication.
On Buprenorphine (Subutex) maintenance treatment
Buprenorphine is a partial opioid agonist with a high affinity for opioid receptors but a low intrinsic activity. It takes around 15 hours to dissociate from opioid receptors during which time it can essentially act as an opioid antagonist.
For patients who need inpatient pain management, the buprenorphine dose should be confirmed with the GP or community pharmacy. Patients have better outcomes if the buprenorphine is continued during the hospital stay but given in two or three divided doses rather than as a single daily dose. This allows an increase in free opioid receptors for the effective use of short acting morphine or oxycodone for acute pain.
Patients not on an opioid substitution programme, but taking unknown amounts of illicit drugs.
These patients will also be opioid tolerant and at risk of withdrawal, but their opioid replacement needs will be harder to assess.