Keflex Side Effects

Generic name: cephalexin

Medically reviewed by Drugs.com. Last updated on Oct 2, 2023.

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

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

Serious side effects of Keflex

Along with its needed effects, cephalexin (the active ingredient contained in Keflex) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while 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 or rash
• joint or muscle pain
• light-colored stools
• loss of appetite
• nausea and vomiting
• 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
• swollen or painful glands
• tightness in the chest
• unusual bleeding or bruising
• unusual weight loss
• watery or bloody diarrhea

Other side effects of Keflex

Some side effects of cephalexin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

• Acid or sour stomach
• anxiety
• belching
• burning feeling in the chest or stomach
• difficulty with moving
• dry mouth
• heartburn
• 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 sleeping
• white or brownish vaginal discharge

For Healthcare Professionals

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

General

The most commonly reported side effects included diarrhea, dyspepsia, gastritis, nausea, and vomiting.^[Ref]

Gastrointestinal

Frequency not reported: Diarrhea, nausea, vomiting, dyspepsia, gastritis, abdominal pain, anal pruritus, Clostridium difficile-associated diarrhea/colitis/pseudomembranous colitis

Postmarketing reports: Colitis^[Ref]

Hematologic

Frequency not reported: Direct Coombs' test seroconversion, decreased prothrombin activity/prolonged prothrombin time, eosinophilia, neutropenia, thrombocytopenia, hemolytic anemia

Postmarketing reports: Aplastic anemia, pancytopenia, leukopenia, agranulocytosis^[Ref]

Dermatologic

Frequency not reported: Urticaria, rash, erythema multiforme, Stevens Johnson syndrome, toxic epidermal necrolysis/exanthematic necrolysis^[Ref]

Hepatic

Frequency not reported: Transient hepatitis, cholestatic jaundice, AST and ALT elevations

Postmarketing reports: Increased bilirubin^[Ref]

Hypersensitivity

Frequency not reported: Hypersensitivity/allergic reactions, angioedema, anaphylaxis^[Ref]

Allergic reactions (including urticaria and angioedema) usually subsided upon treatment discontinuation.^[Ref]

Genitourinary

Frequency not reported: Genital pruritus, genital candidiasis, vulvovaginitis/vaginitis and vaginal discharge^[Ref]

Nervous system

Frequency not reported: Seizure, dizziness, headache^[Ref]

Psychiatric

Frequency not reported: Agitation, confusion, hallucinations^[Ref]

Musculoskeletal

Frequency not reported: Arthralgia, arthritis, joint disorder^[Ref]

Renal

Frequency not reported: Reversible interstitial nephritis

Postmarketing reports: Renal dysfunction, toxic nephropathy, increased blood urea nitrogen, increased creatinine^[Ref]

Other

Frequency not reported: Fatigue

Postmarketing reports: Fever^[Ref]

Immunologic

Frequency not reported: Development of drug-resistant bacteria development^[Ref]

Metabolic

Postmarketing reports: Increased alkaline phosphatase, increased lactate dehydrogenase (LDH)^[Ref]

Cardiovascular

Postmarketing reports: Hemorrhage^[Ref]

Frequently asked questions

• What are the best antibiotics for a tooth infection?
• What is the best antibiotic to treat strep throat?
• Can Cephalexin treat an abscess in the mouth or gum infection?
• If people are allergic to amoxicillin can they take cephalexin?
• Can you take cephalexin for a spider bite?
• Can you take antibiotics while pregnant?
• Cephalexin - is this a drug that can be abused by teens?

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

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