Methadone to opioid (opiate) equivalences

Opioid : Methadone equivalent dosages

It will be necessary to seek expert advice before prescribing in opioid abuse unless a prescriber is a clinician with specialist knowledge in this area.

The following is a guide to the pharmacological equivalents of opioids compared to methadone. It must be emphazised that daily dosages in practice may not be the same ratios. This is because drug half-lives must also be taken into account, so that relatively higher dosages are required of shorter-acting drugs - including dihydrocodeine, morphine and diamorphine - where repeated dosing in a day is required.

* this is what is generally required clinically - given that usually purity of street heroin is 20-30%

Notes:

• direct equivalence between buprenorphine and methadone is difficult to estimate and is not a linear relationship, 12 to 16 mg buprenorphine is approximately as effective as 50 to 80 mg methadone in reducing heroin use and retaining patients in treatment (2)
• for patients who are using other opioids it is sometimes necessary to stabilise them onto methadone or buprenorphine (3)
  • it is not possible to accurately predict equivalent doses in most cases. This is especially true for street drugs where purity is notoriously variable. It is also problematic to convert from one drug to another when the half lives are not equivalent
  • clinicians must apply careful clinical judgment and monitor the progress of treatment carefully, especially during the early stages of treatment. Reference to any conversion table is insufficient on its own, and can only ever be a partial contribution to the necessity of ongoing clinical assessment and monitoring

Reference:

• (1) Seivewright N (2000). Community treatment of drug misuse: more than methadone. Cambridge University Press.
• (2) RCGP (2004). Guidance for the use of buprenorphine for the treatment of opioid dependence in primary care.
• (3) RCGP (2007). Drug misuse and dependence: UK guidelines on clinical management