What the FDA labels say about taking them together
Cyclophosphamide and natalizumab
Cyclophosphamide's FDA label (Frindovyx) of August 26, 2026 names natalizumab in its drug interactions section, and natalizumab's label names cyclophosphamide too. The cyclophosphamide label: “Natalizumab Paclitaxel: Increased hematotoxicity has been reported when cyclophosphamide was administered after paclitaxel infusion.”
Check it at the source: the cyclophosphamide FDA label on DailyMed (effective January 19, 2026, Amneal Pharmaceuticals LLC); the natalizumab FDA label on DailyMed (effective March 21, 2025, Biogen Inc.).
What does the cyclophosphamide label say about natalizumab?
Frindovyx label (AVYXA Pharma, LLC, August 26, 2026), drug interactionsACE inhibitors can cause leukopenia. ● Natalizumab ● Paclitaxel: Increased hematotoxicity has been reported when cyclophosphamide was administered after paclitaxel infusion. ● Thiazide diuretics ● Zidovudine Increased cardiotoxicity ● Anthracyclines ● Cytarabine ● Pentostatin ● Radiation therapy of the cardiac region ● Trastuzumab Increased pulmonary toxicity ● Amiodarone ● G-CSF, GM-CSF (granulocyte colony-stimulating factor, granulocyte macrophage colony-stimulating factor) Increased nephrotoxicity ● Amphotericin B ● Indomethacin:
Cyclophosphamide label (Eugia US LLC, April 21, 2025), drug interactionsNatalizumab Paclitaxel: Increased hematotoxicity has been reported when cyclophosphamide was administered after paclitaxel infusion.
Source: FDA drug label (Frindovyx, NDA210852), AVYXA Pharma, LLC, effective August 26, 2026 (SPL set 5ad8ea65-4c98-487a-9c8d-df778765ec5e), via openFDA
Source: FDA drug label (Cyclophosphamide, NDA210735), Eugia US LLC, effective April 21, 2025 (SPL set 3c1eb470-0bba-457d-94e3-b9508f0d398a), via openFDA
Source: FDA drug label (Cyclophosphamide), Amneal Pharmaceuticals LLC, effective January 19, 2026 (SPL set 520bfe39-dfd5-4a20-9a37-80078afded0d), via openFDA; the full label on DailyMed
What does the natalizumab label say about cyclophosphamide?
Natalizumab label, warnings and precautionsPrior treatment with an immunosuppressant (e.g., mitoxantrone, azathioprine, methotrexate, cyclophosphamide, mycophenolate mofetil).
Source: FDA drug label (TYSABRI), Biogen Inc., effective March 21, 2025 (SPL set c5fdde91-1989-4dd2-9129-4f3323ea2962), 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
| Cyclophosphamide | Natalizumab | |
|---|---|---|
| Labeled for | Leukemia, lymphoma and myeloma | Multiple sclerosis |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $1.67 per capsule 50 mg capsule | 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