What the FDA labels say about taking them together
Nelfinavir and trastuzumab emtansine
Trastuzumab emtansine's FDA label of April 1, 2026 names nelfinavir in its drug interactions section; the nelfinavir label PlainMeds reads does not name trastuzumab emtansine. The trastuzumab emtansine label: “Concomitant use of strong CYP3A4 inhibitors with KADCYLA should be avoided due to the potential for an increase in DM1 exposure and toxicity.”
Check it at the source: the nelfinavir FDA label on DailyMed (effective December 11, 2025, AGOURON); the trastuzumab emtansine FDA label on DailyMed (effective April 1, 2026).
What does the nelfinavir label say about trastuzumab emtansine?
Nelfinavir's label (effective December 11, 2025) does not name trastuzumab emtansine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (VIRACEPT), AGOURON, effective December 11, 2025 (SPL set e72c2bc6-9462-4a2e-8e1d-b97592376cbd), via openFDA; the full label on DailyMed
What does the trastuzumab emtansine label say about nelfinavir?
Trastuzumab emtansine label, drug interactionsConcomitant use of strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, clarithromycin, atazanavir, indinavir, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, and voriconazole) with KADCYLA should be avoided due to the potential for an increase in DM1 exposure and toxicity.
Source: FDA drug label (KADCYLA), Genentech, Inc., effective April 1, 2026 (SPL set 23f3c1f4-0fc8-4804-a9e3-04cf25dd302e), 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
| Nelfinavir | Trastuzumab emtansine | |
|---|---|---|
| Labeled for | HIV | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | n/a |
| Shortage now | No current entry | 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