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Zorluk: ZorPharmacologic Interventions

A 3939-year-old man presents to the addiction medicine clinic complaining of severe muscle aches, abdominal cramping, diarrhea, and rhinorrhea over the past 33 days. He has a history of opioid use disorder and has been stable on a fixed daily dose of oral methadone for the past 22 years without any illicit drug use. Three weeks ago, he was diagnosed with a latent tuberculosis infection after a positive interferon-gamma release assay. He was subsequently started on a daily regimen of oral rifampin, which is planned for a 44-month duration. His vital signs today include a blood pressure of 145/92145/92 mmHg, a heart rate of 110110/min, and a temperature of 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}). Physical examination reveals diaphoresis, pupillary dilation, and hyperactive bowel sounds. A urine toxicology screen is negative for all illicit substances. Which of the following is the most appropriate pharmacologic intervention for this patient's current symptoms?

  1. A
    Administer intramuscular naloxone
  2. B
    Decrease the daily dose of methadone
  3. C
    Discontinue methadone and initiate sublingual buprenorphine-naloxone
  4. Increase the daily dose of methadoneCevap
  5. E
    Maintain the current methadone dose and add oral clonidine

Cevap

Increase the daily dose of methadone
The correct intervention is to increase the daily dose of methadone. Rifampin is a potent inducer of hepatic cytochrome P450 enzymes (specifically CYP3A4 and CYP2B6), which are heavily involved in the metabolism of methadone. When rifampin is initiated for the treatment of latent or active tuberculosis in a patient maintained on methadone, it significantly accelerates methadone clearance. This leads to subtherapeutic plasma levels and precipitates acute opioid withdrawal (characterized by myalgias, gastrointestinal distress, diaphoresis, and pupillary dilation). The standard clinical management is to monitor the patient and titrate the methadone dose upward (often by 25%25\% to 50%50\%) until withdrawal symptoms resolve.

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1
Identify the patient's clinical syndrome based on history and physical exam.
The patient exhibits classic signs of acute opioid withdrawal, including diaphoresis, mydriasis, diarrhea, rhinorrhea, and tachycardia.
Recognizing the acute syndrome is necessary to determine if the patient is experiencing drug toxicity, an unrelated infection, or withdrawal.
2
Determine the etiology of the withdrawal syndrome in a previously stable patient.
The recent addition of rifampin, a potent cytochrome P450 (CYP3A4) inducer, has accelerated the hepatic metabolism of methadone.
Understanding the pharmacokinetic interaction between rifampin and methadone explains why subtherapeutic levels have developed despite strict medication adherence.
3
Select the appropriate pharmacologic intervention to resolve the syndrome.
The methadone dose must be increased to overcome the enhanced hepatic clearance.
Restoring therapeutic plasma levels of methadone is the definitive treatment for inducer-precipitated withdrawal.

Anahtar Kavram

Drug-drug interactions involving cytochrome P450 induction (e.g., rifampin) can accelerate the metabolism of methadone, necessitating an upward dose titration to prevent or treat opioid withdrawal.
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Pharmacologic Interventions

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