Evaluation of inpatient conversion from high dose methadone to long-acting injectable buprenorphine (LAIB)

Background
Oral opiate substitution therapy (OST) for opiate dependence has been the mainstay of treatment in the UK since the 1980s and is effective. Methadone and buprenorphine are recommended by the National Institute for Health and Care Excellence (NICE) guidelines. However, buprenorphine has some distinct advantages in that it can be titrated more quickly than methadone and, due to its ‘partial-agonist’ effect, has a reduced risk of a fatal overdose and it’s higher affinity for opiate receptors giving a ceiling effect. It causes less respiratory depression which may be helpful in patients with chronic lung conditions. 
When converting from methadone to buprenorphine, NICE recommends reducing the dose of methadone down to 30mg/ day beforehand. However this can be very time consuming for those patients on high doses of methadone, carries an increased risk of relapse to illicit opiate use. On the inpatient unit, we have long offered an option for converting from relatively high doses of methadone to buprenorphine and this was adapted to include long-acting injectable buprenorphine (LAIB). 
Method
The cohort was made up of a case series - the first 20 consecutive patients admitted for an inpatient methadone to buprenorphine conversion. 
The site was a specialist 12 bedded inpatient addiction unit.
Two methods were devised. The first was more straight-forward where the starting methadone dose was <80mg and the second was for those on higher doses of methadone, were anxious about the procedure or needed a managed medical withdrawal from additional substances such as alcohol. 
Endpoints included successful completion of the treatment, any adverse events and the time taken from admission to their first long-acting buprenorphine injection.
Results
95% (19/20) completion rate, no adverse events and an average number of days to their first buvidal injection of 5.3. The average starting dose of methadone was 64mg.  The proportion requiring multi-substance intervention was 40%.
Conclusions
This evaluation confirmed that the inpatient conversion from relatively large doses of methadone to LAIB is safe and well tolerated, with only 1/20 failing to complete the treatment, however that patient left the same day that they arrived.
There was an association between the starting dose of methadone and the first weekly dose of LAIB given (24mg v 32mg), with the boundary around 50-60mg of methadone.  Those on higher doses of methadone took a few days longer to stabilise and receive their first LAIB.
Since we first started to offer this procedure, we have seen referral numbers rapidly increase. We have also seen dramatic improvements in some physical conditions that are adversely affected by large doses of methadone, such as severe COPD. And we look forward to studying that going forward.