Cephalexin: uses, dosing, side effects & brands

The label's §8.1 Pregnancy Risk Summary states that available data from decades of epidemiologic studies and pharmacovigilance case reports with cephalosporins, including cephalexin, in pregnant women have not established drug-associated risks of major birth defects, miscarriage, or adverse maternal or fetal outcomes. It notes these studies have methodologic limitations and cannot definitively establish the absence of risk. Animal reproduction studies in mice and rats showed no evidence of fetal harm. All pregnancies carry a background risk (the label cites a 2%-4% birth-defect and 15%-20% miscarriage background risk in the U.S. general population). Discuss use during pregnancy with your prescriber. This is what cephalexin's FDA label says; whether to use it in pregnancy is your prescriber's decision.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run cephalexin against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 4 cephalexin-containing products in the U.S.: Cephalexin, Keflet, Keflex and Keftab. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, cephalexin is currently marketed as capsule, powder and tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Yes. Our catalog lists 1 generic cephalexin product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.

The FDA's Enforcement database lists at least 5 recall records whose product description mentions cephalexin. The most recent: Cephalexin for Oral Suspension (May 23, 2025). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.

Cephalexin reaches peak blood levels within about an hour, but you feel better over days, not minutes. Expect noticeable improvement in fever, pain, or redness within 2-3 days. If you're not improving by then, contact your prescriber. Finish the entire course even once you feel well — stopping early lets the infection rebound and fuels antibiotic resistance.

Other medicines: we hold source-cited interaction answers for Can you drink alcohol while taking cephalexin (Keflex)?. This is what the FDA label and our cited sources say — it is not a complete list. Your pharmacist can check your own combination.

No — cephalexin (Keflex) is a cephalosporin antibiotic, a different (though related) class from penicillins. Most people with a penicillin allergy can take it, but because the two classes share some structure, a small cross-reactivity risk exists — tell your prescriber about any penicillin allergy.

The most common are diarrhea, nausea, and stomach upset; some people also get mild indigestion or a vaginal yeast infection from the antibiotic. These are usually mild and resolve when the course ends, and taking it with food helps with nausea.

The main serious risk is an allergic reaction, hives, swelling of the face, lips, or throat, and trouble breathing are a medical emergency (anaphylaxis). Because cephalexin is a cephalosporin, people with a severe penicillin allergy have a small risk of cross-reaction, so tell your prescriber about any drug allergies. Also seek care for severe or bloody diarrhea (C. difficile, which can appear even weeks after finishing) and for any blistering or peeling rash.

Tell your doctor, but a reaction is unlikely for most people. Cephalexin is a first-generation cephalosporin, and the cross-reaction rate with penicillin is low, roughly 1 to 2 percent, and mainly a concern if your penicillin reaction was severe, such as anaphylaxis. In that case your prescriber may choose a different antibiotic; a mild past rash usually isn't a barrier.

Mild diarrhea, nausea, or stomach upset during the course are expected and usually don't mean stopping. Stop and get help for any rash, itching, facial or throat swelling, or wheezing (allergy); for watery or bloody diarrhea with cramps; or for yellowing skin. Finish the full prescribed course even if you feel better, unless your doctor tells you to stop.