Nafcillin Injection and Mavacamten: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Mavacamten
Nafcillin Injection
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
Reduced mavacamten exposure and reduced efficacy of mavacamten
Interaction Deep Dive
Concomitant use of mavacamten with a moderate or strong CYP3A4 inducer is contraindicated as it may reduce mavacamten exposure which may also reduce efficacy of mavacamten. Discontinuation of the inducer may increase the risk of heart failure due to systolic dysfunction1.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of mavacamten
Literature reports
1 report — tap to read
a) In a drug interaction study, concomitant use of mavacamten (a single 15 mg dose) with a strong CYP3A4 inducer (rifAMPin 600 mg daily dose) is predicted to decrease mavacamten AUC(0 to inf) and Cmax by 87% and 22%, respectively, in CYP2C19 normal metabolizers, and by 69% and 4%, respectively, in CYP2C19 poor metabolizers 1.
Common questions
Can I take Nafcillin Injection and Mavacamten together?
Reduced mavacamten exposure and reduced efficacy of mavacamten Always confirm with your pharmacist or prescriber before making any change.
How serious is the Nafcillin Injection and Mavacamten interaction?
It is rated contraindicated. These should generally not be used together.
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 Nafcillin Injection or Mavacamten 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: CAMZYOS(R) oral capsules, mavacamten oral capsules. Bristol-Myers Squibb Company (per Manufacturer), Princeton, NJ, 2025. DailyMed
Keep reading about Mavacamten
Keep reading about Nafcillin Injection
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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