Pentazocine, a mixed agonist-antagonist opioid, is contraindicated in patients with myocardial infarction requiring analgesia. This is primarily because pentazocine:

• A Increases pulmonary artery pressure and cardiac workload via kappa receptor agonism and sigma receptor activity ✓
• B Causes direct myocardial depression exceeding that of morphine
• C Is a full mu agonist with higher respiratory depression risk than morphine
• D Inhibits platelet aggregation and increases bleeding risk in acute coronary syndrome

Explanation

Pentazocine is a kappa receptor agonist and sigma receptor agonist. This combination increases pulmonary artery pressure and systemic vascular resistance, thereby increasing cardiac workload. In myocardial infarction, this increased oxygen demand is harmful. It is not a full mu agonist and does not cause more respiratory depression than morphine. The cardiac workload effect is the primary contraindication.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.