Keflex - Interactions | Dosage | Side Effects

This article was medically reviewed by M.Pharm, Marko Tanaskovic on August 12, 2018. To read more about an author, click here.

Keflex containts active substance called Cephalexin. Mechanism of action of this medicine is based on interfering with synthesis of bacteria cell wall, which leads to elimination of bacteria. It is one of the most commonly used medicine in the treatment of infections, such as:

  • Upper and lower respiratory tract infections (sinusitis, tonsillitis, pharyngitis, laryngitis and pneumonia);
  • Middle ear inflammation (so-called otitis media);
  • Skin and soft tissue infections. It is one of the most effective medicines in the treatment of skin and soft tissue infections caused by staphylococci and streptococci.1 Research results have shown that it should be considered as first-line therapy.
  • Kidney infections
  • Bladder infections
  • Other genitourinary tract infections
  • Dental infections
  • Acne vulgaris5. Some studies have shown promising results of this medicine for acne treatment.


Keflex may cause allergic reaction. Tell your doctor if you have had allergic reaction to any medicine. Do not use this medicine without your doctor's advice.

You should avoid use of this medicine if you are allergic to any of below listed medicines:

  • Other cephalosporins, such as:
    • cephradine,
    • cefixime,
    • cefepime,
    • cefotetan,
    • cefoperazone,
    • cefazolin,
    • cefaclor,
    • cefprozil,
    • cefoxitin,
    • cefdinir,
    • cefpodoxime,
    • cefpirome and others.
  • Penicillin antibiotics (because of possible cross allergy). Nearly 1 % of patients allergic to penicillin will have an allergic reaction if they take cephalosporin.2

Fortunately, Keflex causes very low incidence of allergy.3

Because most of Keflex is excreted in urine via the kidneys (7 - 100 %), patients with kidney damage require a reduction in Keflex dosage. Also, Keflex may cause acute tubular necrosis (kidney damage)4, and you should be aware of renal impairment symptoms (urinating less often than usual, blood in the urine, difficulty urinating and others). If you are experiencing any of those, you should go to the hospital immediately.


Recommended dosage regimen in adults:

Type of infection Recommended dosage
Bacterial Endocarditis Prophylaxis One dose of 2000 mg
Middle ear infection 500 mg four times a day. Treatment should last 10-14 days.
Skin and soft tissue infections 500 mg three times a day for 7-14 days.
Pharyngitis 500 mg three times a day for at least 7 days.
Cystitis 500 mg three times a day for 7-14 days.
Prostatitis 500 mg four times a day for at least 14 days.
Tonsillitis 500 mg three times a day for 7 days.

Take the tablet one hour before a meals or two hours after meals.


Medicines that should not be used at the same time as Keflex, include:

  • Quinapril (used to treat hypertension, heart failure and to prevent heart attacks). Quinapril decreases levels of Keflex in the blood, thus decrease its efficacy.
  • Warfarin. Concomitant use of Keflex with this medicine may lead to an increase in INR.
  • Metformin (medicine used to treat diabetes). Concomitant use of Keflex with this medicine inhibits renal excretion which causes icnreased concentration of metformin in the blood and increases risk of hypoglicemia.

Side effects

Tell your doctor if you are experiencing any of the following side effects:

  • Painful white patches in the mouth or tongue (oral candidiasis)
  • Vaginal ithcing, and / an abnromal vaginal discharge (vaginal yeast infection)
  • Diarrhea
  • Nausea
  • Vomiting
  • Dizziness
  • Unusual tiredness
  • Exhaustion
  • Abdominal pain
  • Headache

You must inform your doctor if you experience:

  • Skin rash;
  • Swelling of the face, lips, tongue or neck which may cause difficulty breathing;
  • Fever;
  • Swelling of the joints;
  • Yellowing of the skin and eyes;
  • Joint pain;
  • Confusion
  • Hallucinations
  • Bleeding
  • Easy bruising.

This list includes serious side effects that require immediate medical attention.

Brand names: References:

  1. Derrick CW, Reilly K. The role of cephalexin in the treatment of skin and soft-tissue infections. Postgrad Med J. 1983: 59: 43-6.
  2. Campagna JD, Bond MC, Schabelman E, and others. The use of cephalosporins in penicillin-allergic patients: a literature review. J Emerg Med. 2012: 42 (5): 612-20.
  3. Griffith RS. The pharmacology of cephalexin. Postgrad Med J. 1983: 59: 16-27.
  4. Longstreth KL, Robbins SD, Smavatkul C, and others. Cephalexin-induced acute tubular necrosis. Pharmacotherapy. 2004: 24 (6): 808-11.
  5. Fenner JA, Wiss K, Levin NA. Oral cephalexin for acne vulgaris: clinical experience with 93 patients. Pdeiatr Dermatol. 2008: 25 (2): 179-83.

Information on this website are provided for educational purposes only and are not intended for medical advice, diagnosis or treatment.

If you have any concerns or questions about your health, you should always consult with a physician or other health-care professional.

We and our partners use technology such as cookies on our site to personalise content and ads, provide social media features, and analyse our traffic. Click below to consent to the use of this technology across the web. You can change your mind and change your consent choices at anytime by returning to this site.