What the FDA labels say about taking them together
Siltuximab and theophylline
Siltuximab's FDA label of August 27, 2024 names theophylline in its drug interactions section; the theophylline label PlainMeds reads does not name siltuximab. The siltuximab label: “Upon initiation or discontinuation of SYLVANT, in patients being treated with CYP450 substrates with a narrow therapeutic index, perform therapeutic monitoring of effect (e.g., warfarin) or drug concentration as needed …”
Check it at the source: the siltuximab FDA label on DailyMed (effective August 27, 2024); the theophylline FDA label on DailyMed (effective March 10, 2026, Strides Pharma Science Limited).
What does the siltuximab label say about theophylline?
Siltuximab label, drug interactionsUpon initiation or discontinuation of SYLVANT, in patients being treated with CYP450 substrates with a narrow therapeutic index, perform therapeutic monitoring of effect (e.g., warfarin) or drug concentration (e.g., cyclosporine or theophylline) as needed and adjust dose.
Source: FDA drug label (Sylvant), Recordati Rare Diseases, Inc., effective August 27, 2024 (SPL set 8d663642-f52e-49c0-a023-2da083fdfc0b), via openFDA; the full label on DailyMed
What does the theophylline label say about siltuximab?
Theophylline's label (effective March 10, 2026) does not name siltuximab in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Theophylline), Strides Pharma Science Limited, effective March 10, 2026 (SPL set b7a90ccf-9c32-40cc-9008-7e55b3da4dfd), 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
| Siltuximab | Theophylline | |
|---|---|---|
| Labeled for | n/a | Asthma |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.330 per tablet 300 mg tablet |
| 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