Keflex (cephalexin)

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, and 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. Cephalexin was approved by the FDA in January 1971.

Cephalexin is used to treat infections caused by bacteria that are susceptible to the effects of cephalexin. Common infections that cephalexin is used for include:

• Middle ear infections (otitis media)
• Tonsillitis
• Throat infections
• Laryngitis
• Bronchitis
• Pneumonia
• Urinary tract (UTIs)
• Skin
• Bone infections

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 cephalexin. Serious but rare reactions include seizures, severe allergic reactions (anaphylaxis), and low platelet or red blood cell count.

Cephalexin, like almost all antibiotics, may cause mild or severe cases of pseudomembranous colitis, a mild to severe inflammation of the colon. Antibiotics, including cephalexin alter the types of bacteria in the colon and permit overgrowth of a bacterium called Clostridium difficile. Studies indicate that toxins produced by Clostridium difficile are a primary cause of pseudomembranous colitis.

• The dose of cephalexin for adults is 1 to 4 grams in divided doses.
• The usual adult dose is 250 mg every 6 hours.
• Some infections may be treated with 500 mg every 12 hours.
• Children are treated with 25-100 mg/kg/day in divided doses.
• The dosing interval may be every 6 or 12 hours depending on the type and seriousness of the infection.

Cephalexin may reduce the effect of BCG and typhoid vaccines. Cephalexin should not be combined with BCG or typhoid vaccine unless there are no other options.

Cephalexin is excreted in breast milk. Cephalexin should be used with caution or stopped when breastfeeding.

• Cephalexin is available in generic form. You need a prescription to obtain cephalexin.
• Keflex is the brand name available for cephalexin in the US.
• Cephalexin is available as:
  • Tablets of 250 and 500 mg.
  • Capsules: 250, 500 and 750 mg.
  • Powder for Suspension: 125 and 250 mg/5 ml.
• Cephalexin tablets and capsules should be stored at room temperature, 15 C to 30 C (59 F to 86 F). Suspensions should be refrigerated and discarded 14 days after they have been prepared from the powder.