**Question:** True statement regarding methadone are all except:

A. Methadone is a potent opiate agonist.
B. Methadone is primarily eliminated by the liver.
C. Methadone can cause respiratory depression.
D. Methadone is typically used as a pain reliever in palliative care.

**Core Concept:**
Methadone is a synthetic opioid analgesic drug used in pain management and addiction treatment. It acts as an agonist at the mu-opioid receptors, binding to these receptors and mimicking the effects of naturally occurring opioids like morphine and heroin. Methadone has a long half-life, allowing for once-daily administration. It is primarily eliminated by the liver, which is why understanding the pharmacokinetics of methadone is essential for safe prescribing.

**Why the Correct Answer is Right:**
Option A is correct because methadone is also a μ-opioid receptor antagonist, meaning it can reverse the effects of other opioids and is often used for opioid detoxification.

Option B is incorrect because methadone's primary elimination pathway is through the lungs, not the liver. It is primarily eliminated via pulmonary clearance, particularly by diffusion into the alveolar air and subsequent clearance by the respiratory system.

Option C is correct because methadone can indeed cause respiratory depression due to its opioid effects and potential interactions with other drugs.

Option D is correct because methadone is commonly used in opioid substitution therapy for chronic pain management, particularly in palliative care settings.

**Why Each Wrong Option is Incorrect:**
Option B is incorrect because methadone's primary elimination pathway is through the lungs, not the liver. It is primarily eliminated via pulmonary clearance, particularly by diffusion into the alveolar air and subsequent clearance by the respiratory system.

Option C is incorrect because methadone can cause respiratory depression due to its opioid effects and potential interactions with other drugs. Methadone's long half-life allows for once-daily administration, but this can lead to respiratory depression in cases of overdose, underdosing, or patient-specific factors like underlying respiratory illness or drug interactions.

Option D is incorrect because methadone is typically used as a long-acting opioid for chronic pain management, particularly in palliative care settings. It is often used in substitution therapy for opioid addiction and is a vital part of the treatment for patients with severe chronic pain due to its long acting properties and low incidence of side effects like nausea or vomiting.

Option A is incorrect because methadone serves as both an agonist and antagonist. While it can be used as an agonist (agonizing opioid receptors) for pain management, it can also act as an antagonist (blocking the effects of other opioids) during opioid detoxification procedures.

**Core Concept:** Methadone is a synthetic opioid analgesic drug with dual pharmacological properties (agonist and antagonist). It acts as an agonist at the μ-opioid receptors, blocking the effects of other opioids (antagonist) during opioid detoxification procedures.

**Why Each

✓ Correct Answer: D. The onset of analgesia is 30-60 minutes after parenteral administration and 1-2 hours after oral administration