What the FDA labels say about taking them together
Methotrexate and sapropterin
Sapropterin's FDA label of August 26, 2024 names methotrexate in its drug interactions section; the methotrexate labels PlainMeds reads (4) do not name sapropterin. The sapropterin label: “Inhibitors of Folate Synthesis Clinical Impact In vitro and in vivo nonclinical data suggest that drugs that inhibit folate synthesis may decrease the bioavailability of endogenous BH4 by inhibiting the enzyme …”
Check it at the source: the methotrexate FDA label on DailyMed (effective May 27, 2026, Accord Healthcare Inc.); the sapropterin FDA label on DailyMed (effective August 26, 2024, BioMarin Pharmaceutical Inc.).
What does the methotrexate label say about sapropterin?
Methotrexate's label (effective May 27, 2026) and its 3 other brand-application labels do not name sapropterin in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Methotrexate), Accord Healthcare Inc., effective May 27, 2026 (SPL set 874c7f43-a3be-4236-89cc-24c44e3c5813), via openFDA; the full label on DailyMed
What does the sapropterin label say about methotrexate?
Sapropterin label, drug interactionsInhibitors of Folate Synthesis (e.g., methotrexate, valproic acid, phenobarbital, trimethoprim) Clinical Impact In vitro and in vivo nonclinical data suggest that drugs that inhibit folate synthesis may decrease the bioavailability of endogenous BH4 by inhibiting the enzyme dihydrofolate reductase, which is involved in the recycling (regeneration) of BH4. This reduction in net BH4 levels may increase Phe levels. Intervention Consider monitoring blood Phe levels more frequently during concomitant administration. An increased dosage of KUVAN may be necessary to achieve a biochemical response.
Source: FDA drug label (Kuvan), BioMarin Pharmaceutical Inc., effective August 26, 2024 (SPL set af38711e-8873-4790-a92d-4d583e23fb89), 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
| Methotrexate | Sapropterin | |
|---|---|---|
| Labeled for | Rheumatoid arthritis, Psoriasis, Leukemia, lymphoma and myeloma, Breast cancer | n/a |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.158 per tablet 2.5 mg tablet | n/a |
| Shortage now | In shortage | 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