Cephalexin and Dofetilide: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Dofetilide
Cephalexin
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased dofetilide exposure and an increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest)
Interaction Deep Dive
Concurrent administration of dofetilide is contraindicated with renal cation transport inhibitors1, such as cephalexin 23, as concomitant use of drugs that interfere with the renal elimination of dofetilide may increase the risk of arrhythmias such as Torsade de Pointes 1. If coadministration is required, monitor for adverse effects associated with dofetilide, such as cardiac arrhythmias 4.
Why it happens (mechanism)
Inhibition of renal cation transport of dofetilide by cephalexin
Literature reports
1 report — tap to read
a) Metformin and dofetilide are both eliminated in the kidneys by cationic secretion 1; cephalexin is also an inhibitor of renal cation transport 2. The coadministration of single doses of metformin 500 mg and cephalexin 500 mg increased metformin Cmax by 34% and AUC by 24%, and decreased metformin renal clearance by 14% compared with metformin and placebo in a pharmacokinetic study of healthy volunteers (N=12). Following coadministration with cephalexin, renal clearance of metformin was significantly reduced for up to 8 hours. Metformin is excreted through the organic cationic transporter system of the proximal tubules and cephalexin is excreted completely in the urine as unchanged drug. The mechanism of reduced renal clearance of metformin was suspected to be inhibition of tubular secretion via the organic cationic system by cephalexin 3.
Common questions
Can I take Cephalexin and Dofetilide together?
Increased dofetilide exposure and an increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Cephalexin and Dofetilide interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Cephalexin or Dofetilide need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Product Information: TIKOSYN(R) oral capsules, dofetilide oral capsules. Pfizer Labs (per FDA), New York, NY, 2019. DailyMed
- Ivanyuk A, Livio F, Biollaz J, et al: Renal drug transporters and drug interactions. Clin Pharmacokinet 2017; 56(8):825-892. PubMed
- Jayasagar G, Krishna Kumar M, Chandrasekhar K, et al: Effect of cephalexin on the pharmacokinetics of metformin in healthy human volunteers. Drug Metabol Drug Interact 2002; 19(1):41-48. PubMed
- Yamreudeewong W, DeBisschop M, Martin LG, et al: Potentially significant drug interactions of class III antiarrhythmic drugs. Drug Saf 2003; 26(6):421-438. PubMed
Keep reading about Dofetilide
Keep reading about Cephalexin
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist