Mental Health  |  OST Prescribing Pathway - Split Methadone or Suboxone dosing

Mental Health

OST Prescribing Pathway - Split Methadone or Suboxone dosing

For the vast majority of patients adequate stability can be achieved on a once daily dose of methadone or suboxone.


BOPAS is reluctant to institute split dosing of methadone or suboxone without strong indications. Split dosing may initially involve twice daily consumption at the pharmacy or where increased takeaways are given, an increased risk of diversion of methadone or suboxone. There must be clinical evidence that split dosing is indicated for a particular patient. (See serum levels). However where patients are stable this may be a positive and safe intervention in some situations (as outlined below).

If the peak/trough serum level ratio is greater than 2 or 2.5:1 then the patient may be considered to have fast metabolism and/or elimination of methadone or suboxone and split dosing should be considered. (The patient will often complain of post-dose sedation and poor sleep plus marked withdrawal symptoms for some hours pre-dose.) A natural fast metaboliser is likely to remain so.

Partial splitting of the dose may also be considered for stable pregnant patients in the latter half of pregnancy in order to avoid the necessity for increase in the dose, especially for those on doses below 60mg. A single daily dose should be reinstituted following delivery (see Pregnancy and OST).


A small number of women become fast metabolizers of methadone or suboxone in pregnancy. Where this is suspected, obtain trough and peak serum levels and discuss with the BOPAS before instituting split dosing. These women are at greater risk of destabilization in pregnancy and timely assessment and management can prevent this.

Split dosing may also be considered for stable patients in the latter part of a planned withdrawal from methadone or suboxone (usually at doses of 30mg or less) in order to reduce pre-dose withdrawal symptoms and to increase the likelihood of successful completion of withdrawal from methadone or suboxone.

Split dosing may be considered for stable patients to better manage physical pain symptoms by twice-daily peak serum levels.


Split dosing (including the proportions of each dose) requires the approval of the BOPAS

*See Section 5.6 Split Methadone Doses page 40 of New Zealand Practice Guidelines for Opioid Substitution Treatment 2014"


Last updated : Friday, August 21, 2015
Next review date : Saturday, August 20,2016

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