Methadone
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Introduction
Methadone is a synthetic opioid used for pain contril and for treating opioid addiction. It is especially helpful for cancer pain and neuropathic pain. However, it can also be very dangerous, given its long half-life, and many deaths have been reported from respiratory depression (often when used in concert with benzodiazepines).
Similar to diabetes being a state of insulin deficiency, withdrawal is a state of opioid deficiency.
It is highly lipophilic and can be be taken PO, IM, IV, SC, PR, epidurally, and intrathecally.
It is metabolized in the liver, with no active metabolites. It is not dialyzable, making it well-suited for patients with renal failure.
Methadone is a mu agonist. It also inhibits monoamine reuptake and inhibits NMDA receptors.
Indications include:
- uncontrolled pain
- opioid toxicity or allergy
- neuropathic pain
History
There are key questions to ask regarding methadone use:
- what is the daily dose?
- when was your last dose?
- are they at a stable dose (for the past week?)
- is their dose working for you?
- withdrawal symptoms (see below), including diurnal variation
- are they clean?
- if they are using, what are they using? What route?
- do they have hepatitis C?
- do they have a concurrent disorder - depression, anxiety, PTSD?
- do they have carries?
Asking questions to people who are on methadone needs to be done sensitively. They often have low self-esteem and are sensitized by family and friends.
Take whatever you think about something and set it aside.
Methadone Dosing
Normally, for addicition treatment, daily dosing is 50-120mg. Dosing, however, is not correlated with the severity of their condition. Equivalency cannot be calculated.
If methadone is being used to treat addiction, tolerance does not exist. A successful dose will remain a successful dose.
If methadone is being used to treat pain, by and large, tolerance does not exist. If escalating pain is experienced, be on the lookout for depression or somatic manifestations.
Dose escalation is very dangerous, especially with the presence of other medications.
As endorphins are stress hormones, doses often need to be increased during times of significant stress.
When dosing in hospital, it should be given in juice and should be witnessed.
Half-life is 22 hours.
Duration of action is typically 3-6 hours on initiation and 8-12 hours with repeated dosing. Plasma steady-state levels are usually reached in 5-7 days.
Methadone works for 8-12h for analgesia
24h for addiction
Conversion from other opioids
It is very important to beware of sedation during conversion. Some providers increase the dose every three days rather than daily.
The dose equivalency of morphine:methadone is 10-20:1 - if the patient is on a total daily dose (TDD) of <1000mg of morphine, divide by 10; if the TDD is >1000mg of morphine, divide by 20.
Withdrawal
Almost all methadone patients want to get off methadone.
A taper downwards can lead to stepwise appearance of withdrawal symptoms
- irritation
- insomnia
- anxiety
- headaches
- abdominal cramping
Pregnancy can increase withdrawal.
Interactions
Cocaine, gravol
A good drug interaction tool should be used.
Opioid antagonists or partial agonists
Inducers of Cyt P-450
- dilantin
Inhibitors of CYT P-450
- grapefruit juice
Synergism
- benzodiazepines
pain-topics.org/pdf/Methadone-Drug_Intx_2006.pdf
Overdose
Opioid relapse rate is 50%
Testing
12 Lead ECG: can have prolonged QT
urine testing is done on the metabolite EDDP.
Resources and References
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