What the FDA labels say about taking them together
Isavuconazonium and ritonavir
Isavuconazonium's FDA label of April 25, 2025 names ritonavir in its contraindications section; the ritonavir label PlainMeds reads does not name isavuconazonium. The isavuconazonium label: “Coadministration of CRESEMBA with strong CYP3A4 inhibitors such as ketoconazole or high-dose ritonavir and strong CYP3A4 inducers such as rifampin, carbamazepine, St. …”
Check it at the source: the isavuconazonium FDA label on DailyMed (effective April 25, 2025, Astellas Pharma US, Inc.); the ritonavir FDA label on DailyMed (effective July 23, 2026, AbbVie Inc.).
What does the isavuconazonium label say about ritonavir?
Isavuconazonium label, contraindicationsCoadministration of strong CYP3A4 inhibitors, such as ketoconazole or high-dose ritonavir (400 mg every 12 hours), with CRESEMBA is contraindicated because strong CYP3A4 inhibitors can significantly increase the plasma concentration of isavuconazole [see Drug Interactions ( 7 ) and Clinical Pharmacology ( 12.3 )].
Isavuconazonium label, drug interactionsThe Effect of CRESEMBA on the Pharmacokinetics of Other Drugs Recommendation Comments Lopinavir/ritonavir 400 mg of lopinavir in combination with 100 mg of ritonavir.
Isavuconazonium label, warnings and precautionsCoadministration of CRESEMBA with strong CYP3A4 inhibitors such as ketoconazole or high-dose ritonavir and strong CYP3A4 inducers such as rifampin, carbamazepine, St. John’s wort, or long acting barbiturates is contraindicated [see Contraindications ( 4 ) and Drug Interactions ( 7 )].
Source: FDA drug label (CRESEMBA), Astellas Pharma US, Inc., effective April 25, 2025 (SPL set 8f7f73b8-586a-4df0-935f-fecd4696c16c), via openFDA; the full label on DailyMed
What does the ritonavir label say about isavuconazonium?
Ritonavir's label (effective July 23, 2026) does not name isavuconazonium 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
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
| Isavuconazonium | Ritonavir | |
|---|---|---|
| Labeled for | n/a | HIV |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $114.00 per capsule 186 mg capsule | $0.607 per tablet 100 mg tablet |
| Shortage now | No current entry | A presentation being discontinued |
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