What the FDA labels say about taking them together
Elbasvir/grazoprevir and nafcillin
Elbasvir/grazoprevir's FDA label of March 13, 2026 names nafcillin in its drug interactions section; the nafcillin labels PlainMeds reads (2) do not name elbasvir/grazoprevir. The elbasvir/grazoprevir label: “Co-administration of ZEPATIER with nafcillin may lead to reduced therapeutic effect of ZEPATIER. Co-administration is not recommended.”
Check it at the source: the elbasvir/grazoprevir FDA label on DailyMed (effective March 13, 2026, Merck Sharp & Dohme LLC); the nafcillin FDA label on DailyMed (effective March 9, 2026, ONESOURCE SPECIALTY PHARMA LIMITED).
What does the elbasvir/grazoprevir label say about nafcillin?
Elbasvir/grazoprevir label, drug interactionsConcomitant Drug Class/Drug Name: Antibiotics: Nafcillin; Effect on Concentration ↓ = decrease, ↑ = increase: ↓ EBR ↓ GZR; Clinical Comment: Co-administration of ZEPATIER with nafcillin may lead to reduced therapeutic effect of ZEPATIER. Co-administration is not recommended.
Source: FDA drug label (ZEPATIER), Merck Sharp & Dohme LLC, effective March 13, 2026 (SPL set 164dc02a-9180-426a-b8b5-04ab39d2bbd4), via openFDA; the full label on DailyMed
What does the nafcillin label say about elbasvir/grazoprevir?
Nafcillin's label (effective March 9, 2026) and its 1 other brand-application label do not name elbasvir/grazoprevir in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (NAFCILLIN SODIUM), ONESOURCE SPECIALTY PHARMA LIMITED, effective March 9, 2026 (SPL set 4b3b8e52-df96-4886-e063-6294a90ac63f), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Elbasvir/grazoprevir | Nafcillin | |
|---|---|---|
| Labeled for | Hepatitis C | n/a |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | n/a | n/a |
| Shortage now | A presentation being discontinued | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once