What the FDA labels say about taking them together
Ritonavir and trastuzumab emtansine
Trastuzumab emtansine's FDA label of April 1, 2026 names ritonavir in its drug interactions section; the ritonavir 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 ritonavir FDA label on DailyMed (effective July 23, 2026, AbbVie Inc.); the trastuzumab emtansine FDA label on DailyMed (effective April 1, 2026).
What does the ritonavir label say about trastuzumab emtansine?
Ritonavir's label (effective July 23, 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 (Norvir), AbbVie Inc., effective July 23, 2026 (SPL set 2849298e-de6e-47bb-8194-56e075b33fc3), via openFDA; the full label on DailyMed
What does the trastuzumab emtansine label say about ritonavir?
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
| Ritonavir | Trastuzumab emtansine | |
|---|---|---|
| Labeled for | HIV | Breast cancer |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.607 per tablet 100 mg tablet | 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