What the FDA labels say about taking them together
Phenobarbital and theophylline
Theophylline's FDA label of March 10, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name theophylline. The theophylline label: “30% increase Phenobarbital (PB) Similar to aminoglutethimide.”
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the theophylline FDA label on DailyMed (effective March 10, 2026, Strides Pharma Science Limited).
What does the phenobarbital label say about theophylline?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name theophylline in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), via openFDA; the full label on DailyMed
What does the theophylline label say about phenobarbital?
Theophylline label, drug interactions30% increase Phenobarbital (PB) Similar to aminoglutethimide.
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
| Phenobarbital | Theophylline | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Asthma |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $0.330 per tablet 300 mg tablet |
| 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