Sulfaphenazole and Aficamten: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Aficamten
No brand names on recordSulfaphenazole
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased aficamten exposure and an increased risk of aficamten-related adverse reactions
Interaction Deep Dive
Concomitant use of aficamten with sulfaphenazole (strong CYP2C9 inhibitor) may increase aficamten exposure, which may increase the risk of developing heart failure due to systolic dysfunction. Initiate aficamten at 5 mg in patients on stable therapy with sulfaphenazole. In patients who initiate sulfaphenazole, reduce the dose of aficamten (20 mg to 10 mg; 15 mg to 5 mg; 10 mg to 5 mg). For patients currently receiving aficamten 5 mg, maintain the 5 mg dose. Assess LVEF and LVOT-G 2 to 8 weeks after inhibitor initiation and titrate the dose of aficamten: LVEF greater than or equal to 55%, Valsalva LVOT-G greater than or equal to 30 mmHg: increase the dose by 5 mg (up to the maximum dose of 20 mg once daily). For LVEF greater than or equal to 55%, Valsalva LVOT-G less than 30 mmHg or LVEF less than 55% and greater than or equal to 50%, Valsalva LVOT-G (any): maintain dose. For LVEF less than 50% and greater than or equal to 40%, Valsalva LVOT-G (any): reduce dose by 5 mg (if already on 5 mg, interrupt treatment for at least 7 days). LVEF less than 40%. Valsalva LVOT-G (any): interrupt treatment for 7 days1.
Why it happens (mechanism)
Inhibition of CYP2C9-mediated metabolism of aficamten
Common questions
Can I take Sulfaphenazole and Aficamten together?
Increased aficamten exposure and an increased risk of aficamten-related adverse reactions Always confirm with your pharmacist or prescriber before making any change.
How serious is the Sulfaphenazole and Aficamten interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Sulfaphenazole or Aficamten need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: MYQORZO™ oral tablets, aficamten oral tablets. Cytokinetics, Incorporated (per Manufacturer), South San Francisco, CA, 2025. DailyMed
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