Rx required in the US, UK, and Canada

Cephalexin

Also called Keflex. First-generation cephalosporin.

Some skin, throat, ear, and urinary infections caused by susceptible bacteria. Often used for non-purulent cellulitis.

Last reviewed 2 November 2026. RxNorm 2231. SNOMED CT substance 387304003.

What cephalexin treats

Primary uses clinicians actually reach for this drug for. Local resistance and your own history can take a use off the list.

Non-purulent cellulitis and some other skin infections caused by streptococci, when the area is not an emergency.
Some streptococcal throat infections, often for about 10 days when a cephalosporin is chosen.
Some ear and respiratory infections, and some urinary infections when the local bacteria are still susceptible. E. coli resistance limits its use as a UTI default.

Clinicians sometimes use the twice-daily skin schedule rather than four times a day. That is a prescribing choice, not a schedule to invent because four times a day is inconvenient.

What it does not treat

Colds, flu, COVID-19, and bronchitis
MRSA skin infections as a default. Cephalexin does not cover MRSA.
A boil that needs drainage
A viral sinus infection in the first week
A tooth abscess instead of a dentist

Forms, dosing examples, and how to take it

Forms

Capsules, commonly 250 mg and 500 mg
Tablets
Oral suspension

Adult examples

Adult labeling clusters around a few schedules. The daily maximum on many labels is 4 grams. You do not use that maximum to “cover” a missed diagnosis.

Educational examples only. Not a dosing instruction for a named patient.
Situation	Example adults may see on a label or guideline	Limit
Many adult infections on labeling	250 mg every 6 hours	A common starting pattern. Duration depends on the site.
Some streptococcal throat and skin infections	500 mg every 12 hours	Often about 10 days for strep when this drug is selected.
More severe infections on labeling	500 mg every 6 hours	Spreading redness, fever, or severe pain belongs in an exam room, not in a higher self-selected dose.

Food, minerals, and administration

Cephalexin can be taken with or without food. Food helps if it nauseates you.
Space the doses as evenly as the label says. A four-times-daily plan that becomes “whenever I remember” underdoses the infection.
Tell the clinician about kidney disease, warfarin, and any penicillin or cephalosporin reaction.
Suspension needs the pharmacy measuring device.

Can an online doctor prescribe cephalexin?

Yes only inside the narrow band below. The same visit is supposed to refuse the drug outside that band.

When a prescription is plausible

Yes for some limited skin infections and other susceptible infections a remote clinician can see well enough, often with a photo or video, when there is no fever and the redness is not racing.
A boil, a diabetic foot, or redness that is moving is an in-person visit.

What the visit should cover

Penicillin and cephalosporin reaction details, including whether there was anaphylaxis.
How fast the skin is changing, and whether there is pus, fever, or red streaking.
Kidney function, pregnancy, and other medicines.
Whether MRSA is likely. Cephalexin will not treat that pattern.

When the clinician should refuse

A history of anaphylaxis to penicillin or to a cephalosporin, unless a clinician who understands the side-chain issue documents a different plan.
Purulent MRSA-type infections, rapidly spreading redness, purple skin, or fever with a skin infection.
A cold or a request for Keflex “just in case.”
A dental abscess with no dental follow-up.

How same-day e-prescriptions and local pickup work. If the drug is prescribed, use a pharmacy you can reach today. Mail order is the wrong speed for an acute infection.

Side effects, allergies, pregnancy, and alcohol

Often mild

Nausea
Diarrhea
Stomach discomfort
Yeast infection

Get care

Allergic swelling, wheezing, or fainting
Severe watery diarrhea
A blistering rash
Bloody or prolonged diarrhea after the course ends

Allergies and cross-reaction

Older teaching said about 10 percent of penicillin-allergic people react to cephalosporins. Better data put the overall cross-reaction much lower, but it is not zero. Cephalexin shares a similar side chain with amoxicillin, so the risk is more relevant than it is for many later-generation cephalosporins. After hives, wheezing, or anaphylaxis, do not test cephalexin at home.

Pregnancy

Cephalexin is often used in pregnancy when a susceptible infection needs a cephalosporin. The prescriber still chooses it. Do not borrow a partner’s capsules.

Alcohol

No disulfiram-style warning. Alcohol can worsen nausea and dizziness. It does not turn a viral illness into a cephalexin indication.

Severe watery diarrhea during or after any antibiotic can be C. difficile. Mouth or throat swelling is an emergency: call 911 or 999.

Generic, coupon, and telehealth pickup

These are budgeting bands for a common U.S. generic fill, not a national average and not a GoodRx quote. Discount-card prices change by pharmacy and ZIP code, and a card usually cannot be combined with insurance on the same fill. A telehealth visit is a separate bill, often advertised around $29 to $129 in late October 2026. The medicine is extra. Ask the pharmacy for today’s cash price and today’s coupon price before you travel.

Average-style planning bands for budgeting. Confirm the live cash price and the live coupon.
Product	U.S. cash planning band	Discount-card band, GoodRx-type	Telehealth plus local pickup
Generic cephalexin 500 mg, about 20 to 28 capsules	Often about $10–$30	Often about $6–$20	Visit fee plus local generic pickup.
Brand Keflex	Often several times the generic price	Rarely worth it for the same ingredient	Ask the pharmacist to fill generic cephalexin unless a specific product was required.

Questions about cephalexin

Can I take Keflex if I am allergic to penicillin?

Maybe, and maybe not. A mild, remote, non-severe reaction is a different story from anaphylaxis. Cephalexin is one of the cephalosporins most likely to cross-react with amoxicillin because of a similar side chain. Tell the clinician exactly what happened. Do not try one capsule as a test.

Can telehealth prescribe cephalexin for a skin infection?

Sometimes, for a small warm patch that is not spreading and not paired with fever. Photos miss depth and speed. Fever, pus, a diabetic foot, or redness that moves the same day should be seen in person.

Does cephalexin treat a tooth infection?

Only as an adjunct, and only if a clinician chooses it. The tooth still needs a dentist. Face or neck swelling is an emergency.

What should I do if I miss a dose?

Take a missed dose when you remember unless it is close to the next dose. Skip it then. Do not take two doses at once. If you vomit soon after a dose, ask the pharmacist before you repeat it. The label and the pharmacist outrank this sentence.

Can I drink alcohol with cephalexin?

There is no Flagyl-type reaction. Drinking while nauseated or dizzy is still a bad idea, and alcohol does not treat cellulitis.

Labels: DailyMed. Stewardship: CDC. Pharmacy checks: FDA BeSafeRx. Codes were read from RxNav on 2 November 2026 for ingredient RxCUI 2231.