Keflex Side Effects

Generic Name: cephalexin

Note: This page contains information about the side effects of cephalexin. Some of the dosage forms included on this document may not apply to the brand name Keflex.

Not all side effects for Keflex may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to cephalexin: oral capsule, oral powder for suspension, oral tablet, oral tablet for suspension

In addition to its needed effects, some unwanted effects may be caused by cephalexin (the active ingredient contained in Keflex). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking cephalexin:

More common
  • Diarrhea
Rare
  • Abdominal or stomach pain
  • blistering, peeling, or loosening of the skin
  • chills
  • clay-colored stools
  • cough
  • dark urine
  • diarrhea
  • dizziness
  • fever
  • general tiredness and weakness
  • headache
  • itching
  • joint or muscle pain
  • light-colored stools
  • loss of appetite
  • nausea and vomiting
  • rash
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • sore throat
  • sores, ulcers, or white spots in the mouth or on the lips
  • unpleasant breath odor
  • unusual tiredness or weakness
  • upper right abdominal or stomach pain
  • vomiting of blood
  • yellow eyes or skin
Incidence not known
  • Abdominal or stomach cramps or tenderness
  • back or leg pains
  • black, tarry stools
  • bleeding gums
  • bloating
  • blood in the urine or stools
  • chest pain
  • coughing up blood
  • diarrhea, watery and severe, which may also be bloody
  • difficulty with breathing or swallowing
  • fast heartbeat
  • general body swelling
  • hives
  • increased menstrual flow or vaginal bleeding
  • increased thirst
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
  • loss of appetite
  • nosebleeds
  • pain
  • painful or difficult urination
  • pale skin
  • paralysis
  • pinpoint red spots on the skin
  • prolonged bleeding from cuts
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • red or black, tarry stools
  • red or dark brown urine
  • shortness of breath
  • swollen or painful glands
  • tightness in the chest
  • unusual bleeding or bruising
  • unusual weight loss
  • watery or bloody diarrhea
  • wheezing

Some of the side effects that can occur with cephalexin may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

Incidence not known
  • Acid or sour stomach
  • anxiety
  • belching
  • burning feeling in the chest or stomach
  • difficulty with moving
  • dry mouth
  • heartburn
  • hives or welts
  • hyperventilation
  • indigestion
  • irregular heartbeats
  • irritability
  • itching of the vagina or genital area
  • muscle pain or stiffness
  • nervousness
  • pain during sexual intercourse
  • pain, swelling, or redness in the joints
  • redness of the skin
  • restlessness
  • seeing, hearing, or feeling things that are not there
  • shaking
  • stomach upset
  • trouble with sleeping
  • white or brownish vaginal discharge

For Healthcare Professionals

Applies to cephalexin: oral capsule, oral powder for reconstitution, oral tablet, oral tablet dispersible

General

Cephalexin is generally well-tolerated. Large studies report an overall 6% incidence of side effects, some of which may not be related to cephalexin (the active ingredient contained in Keflex)

Hypersensitivity

Up to 20% of patients with a penicillin allergy may be allergic to cephalexin (the active ingredient contained in Keflex)

Hypersensitivity side effects have included fever, urticaria, rash, eosinophilia, anaphylaxis, angioedema, contact dermatitis, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, acute paronychia, and hepatitis.

Gastrointestinal

Gastrointestinal side effects have included diarrhea, nausea, vomiting, dyspepsia, abdominal cramping, anorexia, and anal pruritus. Diarrhea due to Clostridium difficile colitis has been reported with some cephalosporins.

If diarrhea occurs and it does not resolve with discontinuation of the drug and/or institution of standard antidiarrheal therapy, pseudomembranous colitis should be suspected.

Hepatic

Hepatic side effects have included transient elevations of liver function tests, transient hepatitis, and rare cases of cholestatic jaundice.

Renal

Renal side effects have rarely included interstitial nephritis. Reversible fever, azotemia, pyuria and eosinophiluria are the hallmarks of cephalosporin-induced interstitial nephritis. Acute tubular necrosis has also been reported.

Hematologic

Hematologic side effects have included eosinophilia, neutropenia, thrombocytopenia and hemolytic anemia.

Nervous system

Nervous system side effects have included dizziness, fatigue, headache, agitation, confusion, and hallucinations. Reversible ototoxicity and vertigo, apparently due to labyrinthine disease, have been reported in a few patients with renal disease.

Genitourinary

Genitourinary side effects have included genital pruritus, genital moniliasis, vaginitis, and vaginal discharge.

Musculoskeletal

Musculoskeletal side effects have included arthralgia, arthritis, and joint disorder.

Dermatologic

Dermatologic side effects have included urticaria, rash, contact dermatitis, erythema multiforme, and toxic epidermal necrolysis. Acute generalized exanthematous pustulosis has been reported.

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