What the FDA labels say about taking them together
Sulfamethoxazole/trimethoprim and warfarin
Sulfamethoxazole/trimethoprim's FDA label of December 30, 2024 names warfarin in its drug interactions section; the warfarin label PlainMeds reads does not name sulfamethoxazole/trimethoprim. The sulfamethoxazole/trimethoprim label: “Warfarin Monitor prothrombin time and INR It has been reported that BACTRIM may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin (a CYP2C9 substrate).”
Check it at the source: the sulfamethoxazole/trimethoprim FDA label on DailyMed (effective December 30, 2024, Sun Pharmaceutical Industries, Inc); the warfarin FDA label on DailyMed (effective May 29, 2026, Amneal Pharmaceuticals LLC).
What does the sulfamethoxazole/trimethoprim label say about warfarin?
Sulfamethoxazole/trimethoprim label, drug interactionsWarfarin Monitor prothrombin time and INR It has been reported that BACTRIM may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin (a CYP2C9 substrate).
Sulfatrim label (Preferred Pharmaceuticals, Inc., September 2, 2026), drug interactionsIt has been reported that sulfamethoxazole and trimethoprim may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin.
Source: FDA drug label (Sulfatrim, NDA018615), Preferred Pharmaceuticals, Inc., effective September 2, 2026 (SPL set cd4932ce-0856-4e99-8baf-70afce1d7ffd), via openFDA
Source: FDA drug label (Bactrim), Sun Pharmaceutical Industries, Inc, effective December 30, 2024 (SPL set f59d0c04-9c66-4d53-a0e1-cb55570deb62), via openFDA; the full label on DailyMed
What does the warfarin label say about sulfamethoxazole/trimethoprim?
Warfarin's label (effective May 29, 2026) does not name sulfamethoxazole/trimethoprim in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Warfarin Sodium), Amneal Pharmaceuticals LLC, effective May 29, 2026 (SPL set 558b7a0d-5490-4c1b-802e-3ab3f1efe760), 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
| Sulfamethoxazole/trimethoprim | Warfarin | |
|---|---|---|
| Labeled for | Bacterial infections, Urinary tract infections, Diarrhea | Blood clots (DVT and PE), Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.0448 per tablet Sulfamethoxazole-tmp ds tablet | $0.093 per tablet 2 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