Methadone or suboxone serum levels are indicated when the clinical picture does not agree with expected/typical responses to a given dose of methadone or suboxone and when this additional clinical information would be of use in making decisions regarding changes in the methadone or suboxone dose.
The serum methadone or suboxone level for a given dose will vary between individuals because of individual tolerance and the influence of other factors (e.g. other medications, pregnancy, individual variations in hepatic metabolism and renal clearance).
Research to date on the clinical application of serum methadone or suboxone levels is inconsistent, generally indicating that the overall clinical picture must be the foundation for any decisions regarding adequacy of methadone or suboxone dose. Serum levels may not provide conclusive information.
Indications for serum level testing:
Clinical situations where serum levels may be useful are:
Serum level testing:
This procedure should be undertaken in liaison with the dispensing pharmacist:
The patient must consume their methadone or suboxone at the pharmacy at approximately the same time for 4 days (usually Mon-Thurs) prior to the blood test/s (on Fri). This is to ensure they reach a steady state for a known dose consumed daily under observation.
On the day of the blood test the patient presents to the laboratory for their trough blood level to be taken before they consume their dose and at the same time they have been consuming for previous four days.
If clinically indicated (see split dosing) a peak blood level is taken 3 ½ to 4 hours after the patient has consumed their dose, and before any takeaway doses are dispensed.
Serum methadone or suboxone levels can be measured using capillary blood samples when venous access is difficult. A 1ml SST tube is sufficient.
Serum level interpretation and guidelines:
Serum methadone or suboxone trough level:
Level to provide 24-hour relief of withdrawal symptoms is 150 to 400 ngm/ml. Many OST patients require a level of 300 to 400 to obtain satisfactory relief of symptoms. Consult BOPAS, if considering increasing the dose of a patient with a trough level above 400 ngm/ml. A small number of patients may need a higher trough level in order to achieve adequate 24-hour relief of withdrawal symptoms.
Serum methadone or suboxone trough and peak levels:
Where the peak: trough ratio is 2 or 2.5:1 or greater then split dosing may be indicated in a stable patient. Consult with the BOPAS, prior to instituting split dosing. See Split methadone or suboxone dosing.
*See Section 5.5 Measuring Methadone Serum Levels page 39 of " New Zealand Practice Guidelines for Opioid Substitution Treatment 2014"
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