What the FDA labels say about taking them together
Ketoconazole and trastuzumab emtansine
Trastuzumab emtansine's FDA label of April 1, 2026 names ketoconazole in its drug interactions section; the ketoconazole 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 ketoconazole FDA label on DailyMed (effective January 28, 2026, E. Fougera & Co. a division of Fougera Pharmaceuticals, LLC); the trastuzumab emtansine FDA label on DailyMed (effective April 1, 2026).
What does the ketoconazole label say about trastuzumab emtansine?
Ketoconazole's label (effective January 28, 2026) 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 (ketoconazole), E. Fougera & Co. a division of Fougera Pharmaceuticals, LLC, effective January 28, 2026 (SPL set cad7c647-34a9-4e4e-83b3-8d78e58f588f), via openFDA; the full label on DailyMed
What does the trastuzumab emtansine label say about ketoconazole?
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
| Ketoconazole | Trastuzumab emtansine | |
|---|---|---|
| Labeled for | Fungal infections | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.249 per gram 2% cream | 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