Methadone or buprenorphine can be used for OST
The rationale behind opioid substitution stems from the fact that the majority of patients who have been dependent on
opioids for a year or longer, will not be able to remain abstinent from opioids, even with optimal support.
Methadone and buprenorphine are used as opioid substitutes.18 These medicines both have gradual onsets of
effect with longer durations of action than the opioids being misused, e.g. oxycodone and morphine, resulting in more
stable serum levels. As a result of this, patients taking methadone or buprenorphine do not experience a “rush” or marked
withdrawal symptoms, and have a reduced desire to use other opioids. For patients with pain, this longer action ameliorates
the sudden onset and rapid wearing off of pain relief of shorter acting opioids and therefore improves pain cover.
Methadone is the more commonly used substitute, as it is more effective in retaining patients in treatment, has been
available for longer and is substantially cheaper than buprenorphine. Buprenorphine is a useful alternative choice, although
its partial agonist action means that it may not achieve enough protection against relapse in all patients. In New Zealand,
only the buprenorphine combined with naloxone (Suboxone) is funded, subject to Special Authority criteria. The naloxone
does not act unless injected – its inclusion in Suboxone is to deter injection (although some drug users will do so anyway).
Long-acting morphine and sustained relapse oxycodone preparation are not effective opioid substitutes.
When patients first begin OST, the opioid substitute is dispensed daily as this becomes an external control that takes
the place of the patient’s diminished internal control. This phase of treatment may last for three to six months. Dispensing
restriction is then gradually relaxed to aid rehabilitation as the patient regains the confidence and ability not to use
doses in advance or by injection.
Patients usually require a minimum of two years of opioid substitution for it to be effective, reflecting how profoundly
opioid dependence affects individuals. Any duration of treatment less than one year would be considered to represent an
opioid detoxification, where the chance of relapse is high. For these reasons alone, prevention of opioid dependence by
careful opioid prescribing is far more preferable than having to treat dependence.
General care of patients undergoing OST
Most general practitioners will not be involved in the day-to-day administration of OST, but there are a number of potential
issues to be aware of when patients receiving OST present in general practice.
Methadone is associated with a number of significant adverse effects. Patients have an increased risk of methadone overdose
in the first two weeks of treatment.18 Titration to an effective dose of methadone can take two to six weeks,
and during this time patients may resort to using alternative supplies, with the potential for fatal misjudgement of dose.
Loss of consciousness through cardiorespiratory depression will require emergency treatment with injectable naloxone.
The most troublesome adverse effects associated with methadone include excessive sweating, dental cavities resulting
from decreased saliva production, sleep apnoea, constipation, osteoporosis, drowsiness and reduced sexual function through
either impotence or loss of libido.18 In general, these adverse effects can be managed symptomatically or
with dose reduction.18 QT prolongation is a recognised risk of methadone treatment, especially in patients
with a family history of QT prolongation, those taking higher doses of methadone and those concurrently taking other QT
prolongating medicines, e.g. antidepressants and antipsychotics. The risk of QT prolongation is also increased in females,
and with increasing age.20
Buprenorphine is not generally associated with overdose, unless the patient is opioid naïve (i.e. inappropriately in
OST). Adverse effects include constipation, nausea, reduced sexual function and drowsiness.
Methadone and buprenorphine have potentially significant interactions with a number of other medicines such as antibiotics
(e.g. ciprofloxacin and erythromycin), antifungals (e.g. fluconazole) and antivirals (e.g. ritonavir).18
Refer to the New Zealand Formulary for full details: www.nzf.org.nz
Not all patients receiving OST will be given “take away” doses. However, those that do should be educated on safe storage
of their medicine. Even small doses of methadone in children can be life-threatening and deaths have been reported in
adolescents who have inadvertently taken methadone when looking for an analgesic at home. Pharmacists should dispense
all opioids in child-resistant packing whenever possible.
Be aware that methadone and buprenorphine provide little, if any, analgesia for acute pain due to increased opioid tolerance
or hyperalgesia. As a result, opioid analgesics are often less effective in managing acute pain in patients undergoing
OST and these patients require higher doses more frequently than usual.18 If a patient has a need for acute
pain relief for a clearly defined condition, discuss appropriate options with their OST provider.
The partial agonist action and high opioid receptor affinity of buprenorphine creates particular challenges for using
additional opioids for analgesia. Because stopping the buprenorphine can destabilise the opioid substitution control,
prescribers are usually faced with providing sufficient short-acting opioids to achieve analgesia. Given that this may
involve substantial doses, inpatient oversight is commonly required.
The 2014 New Zealand Practice Guidelines for OST contain practical and evidence-based information for clinicians on
the clinical assessment and treatment of people with opioid dependence. This document is available from:
The Alcohol & Drug Helpline (0800 787 797) and DHBs can advise on local availability of addiction support.
Community and Alcohol Drug Services (CADS) are offered in most main centres around New Zealand. Resources are also available
Addiction support is also be available through non-government organisations, including the Salvation Army, CareNZ, 12-Step
Programmes (e.g. Narcotics Anonymous, Alcohol Anonymous & Al-Anon) and Tranx.