Cephalexin dosage, forms, and strengths

Cephalexin is an antibiotic (also known as antimicrobial) that is FDA-approved to treat bacterial respiratory tract infections, ear infections, bone infections, skin infections, and genitourinary tract infections. Cephalexin is a generic drug that is part of a class of medicines called cephalosporin antibiotics. It works by preventing bacteria from making cell walls, causing the bacteria to die. 

Related: Learn more about cephalexin 

Cephalexin dosage, forms, and strengths

The chart below shows some common uses for cephalexin, along with standard dosages. These are general guidelines. The duration of treatment is generally 7 to 14 days. However, individual factors such as type and severity of infection, as well as kidney function, are taken into consideration when the healthcare provider determines the appropriate dosage and duration of treatment.

* Dosage and duration may vary by type and severity of infection; the duration of treatment is generally 7 to 14 days.

Cephalexin is available in the following dosage forms:

• Capsules: 250 mg, 500 mg, 750 mg

• Tablets: 250 mg, 500 mg

• Oral suspension: 125 mg/5 mL, 250 mg/5 mL

Cephalexin dosage for adults

Cephalexin is typically taken as a capsule by mouth two, three, or four times daily with or without food. Cephalexin should only be used for bacterial infections. Antibiotics such as cephalexin cannot treat viral infections like the common cold, flu, or COVID-19. Cephalexin dosing depends on the type of infection it is treating. 

Cephalexin dosage for adults:

• Bacterial infections (varies by type and severity of infection): 1000 to 4000 mg by mouth daily divided every 6 or 12 hours

• Streptococcal pharyngitis (strep throat): 500 mg by mouth every 12 hours or 

250 mg by mouth every 6 hours

• Uncomplicated urinary tract infection: 500 mg by mouth every 12 hours or 250 mg by mouth every 6 hours

• Bacterial skin or skin structure infection: 500 mg by mouth every 6 hours

Maximum cephalexin dosage for adults:

The maximum adult dosage is 4000 mg per 24 hours (in two to four equally divided doses). However, older adults or people with kidney disease may have a lower maximum dosage.

Cephalexin dosage for children

The following chart provides information about cephalexin dosage by age and indication. For more information, consult your child’s healthcare provider.

Cephalexin dosage for adults and children over 15 years old with kidney impairment

People with impaired renal function may need a dosage adjustment based on creatinine clearance (CrCl).

• CrCl ≥ 60 mL/min: No adjustment required

• CrCl 30 to 59 mL/min: No adjustment required, but the maximum daily dosage should be 1 gram or less

• CrCl 15 to 29 mL/min: 250 mg every 8 hours or 250 mg every 12 hours

• CrCl 5 to 14 mL/min (not on dialysis): 250 mg every 24 hours

• CrCl 1 to 4 mL/min (not on dialysis): 250 mg every 48 hours or every 60 hours

• There is not enough data to make dosage adjustments for people who are on hemodialysis.

Cephalexin dosage for adults aged 65 years and older

Cephalexin is excreted by the kidneys. People with impaired renal function are at a higher risk of reaction to cephalexin. Also, some drugs in the cephalosporin drug class have been associated with causing seizures, especially in people with kidney problems who took the full dose. Because older adults are more likely to have impaired kidney function, the manufacturer recommends that “care should be taken in dose selection.” 

Cephalexin dosage for bacterial infections

Adults: 1000 to 4000 mg by mouth daily divided every 6 or 12 hours (varies by type and severity of infection)

Pediatric patients: 25 to 50 mg/kg/day by mouth divided every 6 to 12 hours (varies by type and severity of infection)

Patients with kidney impairment: Varies by CrCl—see CrCl section above

Cephalexin dosage for strep throat

Adults: 500 mg by mouth every 12 hours or 250 mg by mouth every 6 hours

Pediatric patients (>1 year old): 20 mg/kg/dose by mouth every 12 hours

Patients with kidney impairment: Varies by CrCl—see CrCl section above

Cephalexin dosage for middle ear infection

Adults: dosage not specified; see bacterial infection dosage for adults

Pediatric patients: 75 to 100 mg/kg/day by mouth divided every 6 or 8 hours

Patients with kidney impairment: Varies by CrCl—see CrCl section above

Cephalexin dosage for uncomplicated UTI

Adults: 500 mg by mouth every 12 hours or 250 mg by mouth every 6 hours 

Pediatric patients: 

• 1 year to 2 years of age: 50 to 100 mg/kg/day by mouth divided every 6 hours

• 3 years to 17 years old: 25 to 50 mg/kg/day by mouth in 2 to 4 divided doses, or for severe infections 50 to 100 mg/kg/day by mouth in 3 to 4 divided doses

Patients with kidney impairment: Varies by CrCl—see CrCl section above

Cephalexin dosage for skin or skin structure infection

Adults: 500 mg by mouth every 6 hours

Pediatric patients: 25 to 50 mg/kg/day by mouth divided every 6 or 12 hours

Patients with kidney impairment: Varies by CrCl—see CrCl section above

Cephalexin dosage for pets

Rilexine is a chewable form of cephalexin indicated for use in dogs only. Rilexine can NOT be used in humans. Rilexine is available as 150 mg, 300 mg, and 600 mg chewable tablets. The usual dose is 22 mg/kg (or 10 mg/lb) of body weight twice a day for 28 days, although dosage and duration may vary based on the veterinarian’s assessment. A lower dose may be given for dogs with kidney problems.

Some veterinarians may prescribe the human form of cephalexin for dogs or cats. The usual dosage is 22 to 40 mg/kg (10 to 18 mg/lb) every 6 to 12 hours, and the duration will depend on the veterinarian's recommendation. 

Regardless of the formulation, a lower dose may be given for pets with kidney problems.

Never give medication to your pet unless under the care of a veterinarian.

RELATED: Is cephalexin safe for dogs?

How to take cephalexin

Cephalexin should be taken as directed by your healthcare professional. 

• Your healthcare provider will tell you how much medicine to use. Do not use more than directed.

• Read and follow the patient instructions for this medicine. If you have any questions, talk to your healthcare provider or pharmacist.

• You can take cephalexin with or without food. Taking your medicine with food or milk may help avoid stomach upset.

• Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses. 

• Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

• Capsule or tablet: Store at room temperature away from heat, moisture, and direct light.

• Oral liquid: Store in the refrigerator for up to 14 days. After 14 days, throw away any unused medicine. Do not freeze.

• Oral liquid: Shake well just before use. Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup. Do not use kitchen measuring tools to measure medication, as they are not as accurate.

Cephalexin dosage FAQs

What are the most common side effects of cephalexin?

The most common adverse reactions of cephalexin are gastrointestinal problems like nausea, vomiting, diarrhea, dyspepsia (heartburn), and abdominal pain (stomach pain). Other common side effects are headache and dizziness.

What is the brand name for cephalexin?

The brand name associated with cephalexin is Keflex. However, Keflex is no longer available in the United States as a brand-name drug. Healthcare providers often still write prescriptions for Keflex, but pharmacies will fill the prescription with generic cephalexin.

What warnings are associated with cephalexin?

• Hypersensitivity to cephalexin or other cephalosporins is a contraindication to using cephalexin. This means it should not be used. If you have a penicillin allergy, consult your healthcare provider for medical advice regarding cephalexin use.

• Allergic or hypersensitivity reactions may occur. A severe allergic reaction (anaphylaxis) is rare. If you take cephalexin and have hives, difficulty breathing, or swelling of the lips, tongue, or face, seek emergency medical treatment right away.

• Clostridium difficile-associated diarrhea (CDAD) is a type of diarrhea that is associated with antibiotics. It can range in severity from mild diarrhea to life-threatening or fatal colitis. CDAD can occur during treatment or up to several months after treatment. Seek medical attention if you experience diarrhea.

• Some drugs in the cephalosporin class may cause seizures, especially in people with kidney problems.

• Tell your healthcare provider if you are pregnant, planning to become pregnant, or breastfeeding. Cephalexin is excreted into breast milk.

How long does it take cephalexin to work?

Pharmacokinetics is the study of how the body processes a drug. Cephalexin is absorbed quickly and reaches its peak level in one hour. However, it may take a few days to start feeling better. And, as mentioned above, it is important to finish the full course of treatment, even if you do start to feel better. 

Cephalexin can be taken without regard to meals, as food does not affect its absorption. Other factors, such as age, kidney function, or other medical conditions, may affect how cephalexin is absorbed. 

How long does cephalexin stay in your system?

The half-life of a drug is how long it takes for half of the drug to clear out of the body. In people with normal kidney function, the half-life of cephalexin is one hour. It takes about five half-lives, or about five hours, for a dose of cephalexin to be eliminated from the body. 

For people with severe kidney problems, the drug stays in the system much longer, and the half-life can be up to 19 to 22 hours. This means a dose of medication can take up to 110 hours (almost 5 days) to be eliminated from the body.

What happens if I miss a dose of cephalexin?

If you miss a dose of cephalexin, take it as soon as you remember. However, if it is almost time for the next dose, wait until then and take your regular dose. Do not double up or take extra medicine to make up for a missed dose. If you are uncertain about what to do, consult your healthcare provider. 

How do I stop taking cephalexin?

Take cephalexin at the dosage and for the duration recommended by your healthcare provider. Do not stop taking the medication early if you start to feel better. Antibiotics must be taken for the full course to prevent the bacteria from coming back and prevent antibiotic resistance. Once you finish the prescribed course of cephalexin, you can stop taking it. There is no need to taper off the medication. 

What is the maximum dosage for cephalexin?

The maximum dosage of cephalexin for adults is 4000 mg (or 4 grams) per day, in divided doses. Children, older adults (65 years and older), or people with decreased kidney function may have a lower maximum dose, which the prescriber can determine.

What interacts with cephalexin?

Food interactions:

Cephalexin is not impacted by food and can be taken without regard to meals. If it is hard on your stomach, you can take it with food, and ask your doctor if you should take probiotic supplements.

Drug Interactions:

• Drugs such as metformin and probenecid can increase the side effects of cephalexin.

What kind of bacteria does cephalexin work against?

Cephalexin works against infectious diseases caused by certain gram-positive bacteria, including:

• Staphylococcus aureus (methicillin-susceptible)

• Streptococcus pneumoniae (penicillin-susceptible)

• Streptococcus pyogenes

And certain gram-negative bacteria, including:

• Escherichia coli (E. coli)

• Haemophilus influenzae

• Klebsiella pneumoniae

• Moraxella catarrhalis

• Proteus mirabilis

Sources

• Cephalexin, DailyMed (2018)

• Cephalexin, PDR

• Cephalexin, MedlinePlus (2016)

• Cephalexin (Rx), Medscape

• Cephalexin, StatPearls (2023)

• Rilexine, DailyMed (2021)

• Cephalexin for dogs and cats, PetPlace Drug Library (2022)