Cephalexin Brand names: Keflex, Keftabs, Biocef
July 22 2016 by Ray Sahelian, M.D.

Cephalexin belongs to a class of antibiotics called cephalosporins. They are similar to penicillin in action and side effects. They stop or slow the growth of bacterial cells by preventing bacteria from forming the cell wall that surrounds each cell. The cell wall protects bacteria from the external environment and keeps the contents of the cell together. Without a cell wall bacteria are not able to survive. Bacteria that are susceptible to cephalexin include Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, E. coli and several others.

How is this antibiotic available?
Cephalexin is prescribed as Tablets: 250 and 500 mg, and 1 g. Capsules: 250, 333, 500 and 750 mg. Cephalexin Powder for Suspension: 125, and 250 mg/5 ml.

Medical and infections conditions where this drug is prescribed

Cephalexin is used to treat infections caused by bacteria that are susceptible to the effects of cephalexin. Common infections that are treated with cephalexin include infections of the middle ear, tonsils, throat, larynx (laryngitis), bronchi (bronchitis) and pneumonia. It also is used for treating urinary tract, skin and bone infections.

Cephalexin Dosage

The dose of cephalexin for adults is 1 to 4 grams in divided doses. Children are treated with 25-100 mg/kg/day in divided doses.

Cephalexin and Pregnancy, Nursing

Based on limited evidence, cephalosporins, including cephalexin, appear to be safe when used during pregnancy. Most cephalosporins are excreted in breast milk. Nursing mothers should avoid using cephalosporins or stop breastfeeding while taking a cephalosporin.

Cephalexin side effects

The most common side effects of cephalexin are diarrhea, nausea, abdominal pain, vomiting, headaches, dizziness, skin rash, fever, abnormal liver tests and vaginitis. Individuals who are allergic to penicillin may also be allergic to it.


Cross-reactivity between penicillins and cephalosporins may be as high as 11% for first-generation cephalosporins and 1% for third-generation cephalosporins, possibly due to the involvement of similar side chains.