Mr. M, age 46, has opioid use disorder (OUD). He is currently stabilized on methadone 80 mg/d but presents to your hospital with uncontrolled atrial fibrillation. After Mr. M is admitted, the care team looks to start amiodarone; however, they receive notice of a drug-drug interaction that may cause QTc prolongation. Mr. M agrees to switch to another medication to treat his OUD because he is tired of the regulated process required to receive methadone. The care team would like to taper him to a different OUD medication but would like Mr. M to avoid cravings, symptoms of withdrawal, and potential relapse.
The opioid epidemic has devastated the United States, causing approximately 130 deaths per day.1 The economic burden of this epidemic on medical, social welfare, and correctional services is approximately $1 trillion annually.2 Research supports opioid replacement therapy for treating OUD.1 Multiple types of opioid replacement therapies are available in multiple dosage forms; all act on the mu-opioid receptor. These include full agonist treatment (eg, methadone) and partial agonist treatment (eg, buprenorphine).3 Alternatively, opioid antagonist therapies (eg, naltrexone) have also been found to be effective for treating OUD.1,2,4 This article focuses on partial agonist treatment for OUD, specifically using a buprenorphine microdosing strategy to transition a patient from methadone to buprenorphine.
Buprenorphine for OUD
Buprenorphine binds with high affinity to the mu-opioid receptor, resulting in partial agonism of the receptor.1,2 Buprenorphine has a higher therapeutic index and lower intrinsic agonist activity than other opioids and a low incidence of adverse effects. Due to the partial agonism at the mu receptor, its analgesic effects plateau at higher doses and exhibit antagonist properties.1,2 This distinct “ceiling” effect, combined with a lower risk of respiratory depression, makes buprenorphine significantly safer than methadone.4 Additionally, it has a lower potential for misuse when used with an abuse deterrent such as naloxone.
Common reasons for transitioning a patient from methadone to buprenorphine include intolerable adverse effects of methadone, variable duration of efficacy, drug-drug interactions, or limited access to an opioid treatment program. Traditional buprenorphine induction requires moderate withdrawal before initiating therapy. Due to buprenorphine’s high affinity and partial agonism at the mu receptor, it competes with other opioids (eg, heroin, methadone) and will abruptly displace the receptor’s full agonist with a lower affinity, resulting in precipitated withdrawal.1,3,5 To avoid precipitated withdrawal, it is recommended to leave a sufficient amount of time between full opioid agonist treatment and buprenorphine treatment, a process called “opioid washout.”1,5 Depending on the duration, amount, and specific opioid used, the amount of time between ending opioid agonist treatment and initiating buprenorphine treatment may vary. As a result, many patients who attempt to transition from methadone to buprenorphine remain on methadone due to their inability to tolerate withdrawal. Additionally, given the risk of precipitating withdrawal, initiating buprenorphine may negatively impact pain control.1
Recently, buprenorphine “microdosing” inductions, which do not require patients to be in opioid withdrawal, have been used to overcome some of the challenges of transitioning patients from methadone to buprenorphine.2
Buprenorphine microdosing techniques
Multiple methods of microdosing buprenorphine have been used in both inpatient and outpatient settings.
Bernese method. In 1997, Mendelson et al6 completed a trial with 5 patients maintained on methadone. They found that IV buprenorphine 0.2 mg every 24 hours did not produce a withdrawal effect and was comparable to placebo.6 Haamig et al5 hypothesized that repetitive administration of buprenorphine at minute doses in adequate dosing intervals would not cause withdrawal. Additionally, because of its high receptor binding affinity, buprenorphine will accumulate over time at the mu receptor. Thus, eventually the full mu agonist (eg, methadone) will be replaced by buprenorphine at the mu receptor as the receptor becomes saturated.4,5
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