What the FDA labels say about taking them together
Metformin and sulfamethoxazole/trimethoprim
Sulfamethoxazole/trimethoprim's FDA label of December 30, 2024 names metformin in its drug interactions section; the metformin labels PlainMeds reads (3) do not name sulfamethoxazole/trimethoprim. The sulfamethoxazole/trimethoprim label: “… are metabolized by CYP2C8 or CYP2C9 or eliminated renally via OCT2 (e.g., metformin). Additional monitoring of blood glucose may be warranted.”
Check it at the source: the metformin FDA label on DailyMed (effective September 3, 2026, Granules India Ltd); the sulfamethoxazole/trimethoprim FDA label on DailyMed (effective December 30, 2024, Sun Pharmaceutical Industries, Inc).
What does the metformin label say about sulfamethoxazole/trimethoprim?
Metformin's label (effective September 3, 2026) and its 2 other brand-application labels do 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 (METFORMIN HYDROCHLORIDE), Granules India Ltd, effective September 3, 2026 (SPL set 73197cb5-3e23-4ac0-b189-f9bc848bce66), via openFDA; the full label on DailyMed
What does the sulfamethoxazole/trimethoprim label say about metformin?
Sulfamethoxazole/trimethoprim label, drug interactionsDrug (s): Oral Hypoglycemics; Recommendation: Monitor blood glucose more frequently; Comments: Like other sulfonamide-containing drugs, BACTRIM potentiates the effect of oral hypoglycemic that are metabolized by CYP2C8 (e.g., pioglitazone, repaglinide, and rosiglitazone) or CYP2C9 (e.g., glipizide and glyburide) or eliminated renally via OCT2 (e.g., metformin). Additional monitoring of blood glucose may be warranted.
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
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
| Metformin | Sulfamethoxazole/trimethoprim | |
|---|---|---|
| Labeled for | Type 2 diabetes | Bacterial infections, Urinary tract infections, Diarrhea |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0145 per tablet 500 mg tablet | $0.0448 per tablet Sulfamethoxazole-tmp ds 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