A 24-year-old man with schizophrenia develops palpitations and a syncopal episode. ECG shows a corrected QT interval of 540 ms. He was recently switched from haloperidol to another antipsychotic. The agent most likely responsible is:
- A Thioridazine ✓
- B Trifluoperazine
- C Fluphenazine
- D Loxapine
Correct answer: A. Thioridazine
Explanation
Among antipsychotics, thioridazine produces the greatest degree of QT prolongation and carries the highest risk of torsades de pointes, which led to its withdrawal from many markets and restriction to second-line use. Among newer agents, ziprasidone also markedly prolongs QT. High-potency piperazine phenothiazines such as trifluoperazine and fluphenazine cause more extrapyramidal symptoms but less QT prolongation. Any patient developing marked QT prolongation on an antipsychotic warrants drug review and electrolyte correction.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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