Keflex (cephalexin) is a first-generation cephalosporin antibiotic prescribed for the treatment of a wide spectrum of bacterial infections. It operates by interfering with the synthesis of the bacterial cell wall, leading to bacterial cell death. This medication is a cornerstone in outpatient management due to its reliable efficacy, favorable safety profile, and excellent oral bioavailability, making it a trusted choice for clinicians combating susceptible pathogens.

Features

• Active Pharmaceutical Ingredient: Cephalexin (as monohydrate)
• Drug Class: First-generation cephalosporin antibiotic
• Administration: Oral (capsules, tablets, and oral suspension)
• Standard Strengths: 250 mg, 500 mg, and 750 mg capsules/tablets; 125 mg/5 mL and 250 mg/5 mL oral suspension
• Mechanism of Action: Bactericidal; inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs)

Benefits

• Effectively eradicates a broad range of susceptible Gram-positive and some Gram-negative bacteria.
• Provides rapid onset of action, with peak serum concentrations occurring within one hour of administration.
• Offers convenient oral dosing, facilitating outpatient treatment and improving patient compliance.
• Demonstrates a well-established and generally favorable safety and tolerability profile for most patient populations.
• Serves as a first-line or alternative treatment for common community-acquired infections, helping to reduce complications and hospital visits.

Common use

Keflex is indicated for the treatment of infections caused by susceptible strains of designated microorganisms. Its primary uses include:

• Respiratory Tract Infections: Pharyngitis, tonsillitis, and acute bronchitis caused by Streptococcus pyogenes (Group A beta-hemolytic streptococci). Note: Penicillin is the usual drug of choice in the treatment and prevention of streptococcal infections, including the prophylaxis of rheumatic fever. Keflex is generally effective in the eradication of streptococci from the nasopharynx; however, substantial data establishing the efficacy of Keflex in the subsequent prevention of rheumatic fever are not available at present.
• Skin and Skin Structure Infections: Uncomplicated cellulitis, furuncles, carbuncles, and abscesses typically caused by Staphylococcus aureus (including penicillinase-producing strains) and/or Streptococcus pyogenes.
• Bone Infections: Osteomyelitis caused by S. aureus and/or Proteus mirabilis.
• Genitourinary Tract Infections: Acute and chronic prostatitis caused by Escherichia coli, P. mirabilis, and Klebsiella pneumoniae. Also used for uncomplicated cystitis.
• Otitis Media: Caused by S. pneumoniae, Haemophilus influenzae, staphylococci, streptococci, and Moraxella catarrhalis.

It is crucial to note that culture and susceptibility testing should be performed to guide therapy, as bacterial resistance is a significant concern.

Dosage and direction

Dosage is based on the specific infection being treated, its severity, and the patient’s renal function. The following are general guidelines for patients with normal renal function (creatinine clearance ≥ 80 mL/min).

• Adults: The usual adult dose is 250 mg to 1 gram every 6 hours, or 500 mg every 12 hours for some indications. A typical regimen for many mild to moderate infections is 500 mg every 12 hours. For more severe infections, 500 mg every 6 hours or 1 gram every 12 hours may be required. The maximum daily dose is 4 grams.
• Children: The recommended total daily dose for children is 25 to 50 mg/kg/day divided into two or four equally spaced doses. For otitis media, a dose of 75 to 100 mg/kg/day divided every 6 hours is recommended. The maximum daily dose for children should not exceed 4 grams.
• Administration: Keflex can be taken with or without food. If gastrointestinal upset occurs, administration with food may be beneficial. The oral suspension should be shaken well before each use. It is imperative that patients complete the entire prescribed course of therapy, even if symptoms subside before the medication is finished, to prevent the development of antibiotic-resistant bacteria.

Dosage must be adjusted in patients with impaired renal function. For creatinine clearance rates of 10-50 mL/min, a maximum dose of 500 mg every 8-12 hours is recommended. For rates below 10 mL/min, a maximum dose of 500 mg every 12-24 hours is advised.

Precautions

• Clostridium difficile-Associated Diarrhea (CDAD): Antibiotic use, including Keflex, can disrupt colon flora and permit overgrowth of C. difficile, leading to diarrhea ranging from mild to life-threatening colitis. This can occur during or months after antibiotic therapy. If diarrhea occurs, evaluate for CDAD.
• Renal Impairment: Keflex is excreted by the kidneys. Patients with significantly impaired renal function require careful dosage adjustment to prevent drug accumulation and potential toxicity.
• Prolonged Use: May result in the overgrowth of non-susceptible organisms, including fungi. Constant observation of the patient is essential. If superinfection occurs during therapy, appropriate measures should be taken.
• Penicillin Allergy: Use with caution in patients with a history of hypersensitivity to penicillins and other beta-lactam antibiotics due to the potential for cross-sensitivity. Cross-allergenicity between penicillins and cephalosporins is estimated to be 5-10%.
• Pregnancy and Lactation: Keflex should be used during pregnancy only if clearly needed. Cephalexin is excreted in human milk in low concentrations. Caution should be exercised when Keflex is administered to a nursing woman.
• Drug-Specific Tests: In individuals with diabetes, a false-positive reaction for glucose in the urine may occur with Benedict’s or Fehling’s solutions or with Clinitest® tablets but not with enzyme-based tests like Tes-Tape®.

Contraindications

Keflex is contraindicated in patients with a known hypersensitivity to cephalexin or any other cephalosporin antibiotic. A history of a severe immediate-type hypersensitivity reaction (e.g., anaphylaxis) to any cephalosporin is an absolute contraindication.

Possible side effect

As with all pharmaceuticals, Keflex can cause side effects, although not everybody gets them. The most common are gastrointestinal in nature and are usually mild and self-limiting.

• Common (≥1%): Diarrhea, nausea, vomiting, dyspepsia, gastritis, abdominal pain.
• Uncommon (0.1% - 1%): Dizziness, fatigue, headache, genital pruritus, vaginitis and vaginal discharge, transient elevations in hepatic enzymes.
• Rare (<0.1%): Allergic reactions (skin rash, urticaria, angioedema), reversible hyperactivity, nervousness, insomnia, confusion, hallucinations, arthralgia, arthritis, joint disorder, eosinophilia, neutropenia, thrombocytopenia, and slight elevations in BUN and serum creatinine. Severe skin reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis) and anaphylaxis are very rare but serious potential side effects.

Drug interaction

• Metformin: Cephalexin may increase the serum concentration of metformin. Monitor for increased metformin effects and potential for lactic acidosis.
• Probenecid: Concomitant administration of probenecid competitively inhibits the renal tubular secretion of cephalexin, resulting in increased and prolonged cephalexin blood levels.
• Warfarin: Some cephalosporins have been associated with a potential to enhance the effect of warfarin and other oral anticoagulants, leading to increased prothrombin time and risk of bleeding. Monitor INR closely.
• BCG Vaccine Live / Cholera Vaccine Live: Antibiotics like Keflex may diminish the therapeutic effect of these live bacterial vaccines.

Missed dose

If a dose is missed, it should be taken as soon as possible. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Do not double the dose to make up for a missed one.

Overdose

Symptoms of overdose are primarily extensions of the drug’s adverse effects and would likely include severe nausea, vomiting, epigastric distress, diarrhea, and hematuria. Serum levels of cephalexin can be reduced by hemodialysis and peritoneal dialysis. Treatment of overdose should be symptomatic and supportive.

Storage

• Store Keflex capsules and tablets at room temperature, 20°C to 25°C (68°F to 77°F), in a tight, light-resistant container. Protect from moisture.
• Store the constituted oral suspension in a refrigerator between 2°C and 8°C (36°F and 46°F). Discard any unused portion after 14 days. Do not freeze.

Disclaimer

This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any new treatment. Never disregard professional medical advice or delay in seeking it because of something you have read here.

Reviews

• Clinical Efficacy (5/5): “As a primary care physician for over 20 years, cephalexin remains a workhorse in my practice for uncomplicated skin and soft tissue infections. Its predictable spectrum against common community pathogens like S. aureus and S. pyogenes and its tolerability make it a first-line choice.” – Dr. A. Reynolds, MD
• Patient Tolerability (4/5): “Prescribed a 10-day course for cellulitis. The infection cleared up completely within a week. Experienced some mild nausea for the first couple of days, but taking it with food completely resolved the issue. Finished the full course without any other problems.” – Mark T.
• Pediatric Use (4/5): “My pediatrician prescribed the suspension for my daughter’s ear infection. The dosing was straightforward with the provided syringe, and she liked the strawberry flavor. Her fever and discomfort resolved within 48 hours. We did notice some loose stools towards the end of the course, but it was manageable.” – Sarah L.
• Convenience (5/5): “The twice-daily dosing schedule for my prostatitis was much easier to adhere to compared to other antibiotics I’ve been on that required four times a day. It fit seamlessly into my daily routine.” – James K.