What the FDA labels say about taking them together
Dofetilide and trimethoprim
Dofetilide's FDA label of April 21, 2026 names trimethoprim in its contraindications section; the trimethoprim label PlainMeds reads does not name dofetilide. The dofetilide label: “The concomitant use of verapamil or the cation transport system inhibitors cimetidine, trimethoprim, or ketoconazole with TIKOSYN is contraindicated, as each of these drugs cause a substantial increase in dofetilide …”
Check it at the source: the dofetilide FDA label on DailyMed (effective April 21, 2026, Pfizer Laboratories Div Pfizer Inc); the trimethoprim FDA label on DailyMed (effective January 26, 2024, Dr. Reddy's Labratories Inc.).
What does the dofetilide label say about trimethoprim?
Dofetilide label, contraindicationsThe concomitant use of verapamil or the cation transport system inhibitors cimetidine, trimethoprim (alone or in combination with sulfamethoxazole), or ketoconazole with TIKOSYN is contraindicated (see WARNINGS and PRECAUTIONS, Drug-Drug Interactions ), as each of these drugs cause a substantial increase in dofetilide plasma concentrations.
Dofetilide label, warningsThe magnitude of the effect on renal elimination by cimetidine, trimethoprim, and ketoconazole (all contraindicated concomitant uses with dofetilide) suggests that all renal cation transport inhibitors should be contraindicated.
Source: FDA drug label (Tikosyn), Pfizer Laboratories Div Pfizer Inc, effective April 21, 2026 (SPL set 02438044-d6a3-49e9-a1ac-3aad21ef2c8c), via openFDA; the full label on DailyMed
What does the trimethoprim label say about dofetilide?
Trimethoprim's label (effective January 26, 2024) does not name dofetilide in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Trimethoprim), NDA018679 (Dr Reddys Labs Sa), as published by Dr. Reddy's Labratories Inc., effective January 26, 2024 (SPL set 73ccebc1-7412-2424-d62c-a5180ec52d81), 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
| Dofetilide | Trimethoprim | |
|---|---|---|
| Labeled for | Atrial fibrillation | Bacterial infections, Urinary tract infections |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.203 per capsule 125 mcg capsule | $1.31 per tablet 100 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