Keflex (cephalexin) is a first-generation cephalosporin antibiotic prescribed for the treatment of a wide spectrum of bacterial infections. It operates by inhibiting bacterial cell wall synthesis, leading to the eradication of susceptible organisms. This makes it a cornerstone in outpatient and some inpatient therapeutic regimens, valued for its reliable bioavailability and established safety profile when used appropriately under medical supervision.

Features

• Active Ingredient: Cephalexin monohydrate
• Drug Class: First-generation cephalosporin antibiotic
• Available Forms: 250 mg, 500 mg, and 750 mg capsules; 125 mg/5 mL and 250 mg/5 mL oral suspensions
• Mechanism of Action: Bactericidal; inhibits cell wall synthesis by binding to penicillin-binding proteins (PBPs)
• Spectrum of Activity: Effective against many Gram-positive and some Gram-negative bacteria, including Staphylococcus aureus (non-MRSA), Streptococcus pyogenes, Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae

Benefits

• Rapid onset of action with peak serum concentrations achieved within one hour of oral administration
• High oral bioavailability, ensuring consistent and predictable systemic drug levels
• Proven clinical efficacy in resolving common bacterial infections such as skin/soft tissue infections, respiratory tract infections, and urinary tract infections
• Generally well-tolerated with a side effect profile that is manageable for most patient populations
• Suitable for both adult and pediatric patients (dose-adjusted by weight), offering flexible treatment options
• Lower risk of Clostridioides difficile infection compared to broader-spectrum antibiotics, when used appropriately

Common use

Keflex is indicated for the treatment of bacterial infections caused by susceptible strains of microorganisms. Common clinical applications include skin and skin structure infections such as cellulitis and impetigo; respiratory tract infections including pharyngitis and tonsillitis; otitis media (middle ear infection); bone infections; genitourinary tract infections, including acute prostatitis and uncomplicated cystitis; and as prophylactic therapy prior to dental procedures in patients with a history of endocarditis or prosthetic joint placement, per specific guidelines. Its use is predicated on confirmed or strongly suspected bacterial etiology, as it is ineffective against viral infections.

Dosage and direction

Dosage is individualized based on the infection’s severity, causative organism, and patient’s renal function. For adults, the typical dose for most infections is 250 mg every 6 hours, or 500 mg every 12 hours. For more severe infections, 500 mg every 6 hours or 1 gram every 12 hours may be required. The total daily dosage for adults should not exceed 4 grams.

For pediatric patients, the recommended dosage is 25 to 50 mg/kg/day divided into two or four doses. For otitis media, doses of 75 to 100 mg/kg/day divided into four doses are commonly used. The maximum pediatric dose should not exceed 4 grams per day.

Keflex should be administered with or without food; however, taking it with food may minimize potential gastrointestinal upset. It is crucial to complete the entire prescribed course of therapy, even if symptoms improve before the medication is finished, to prevent the development of antibiotic resistance.

Precautions

Prior to initiating Keflex therapy, a detailed patient history should be obtained. Use with caution in patients with a history of gastrointestinal disease, particularly colitis, as antibiotic use can cause pseudomembranous colitis. Renal function should be assessed in elderly patients or those with pre-existing renal impairment, as dosage adjustment may be necessary. Prolonged use may result in the overgrowth of non-susceptible organisms, including fungi. If superinfection occurs during therapy, appropriate measures should be taken. As with all antibiotics, Keflex should only be used to treat bacterial infections and is not effective against viral infections (e.g., the common cold).

Contraindications

Keflex is contraindicated in patients with known hypersensitivity to cephalexin or any other cephalosporin antibiotics. Cross-sensitivity with penicillins may occur; therefore, it should be used with extreme caution in individuals with a history of severe allergic reactions (e.g., anaphylaxis) to penicillins or other beta-lactam antibiotics.

Possible side effect

The most common side effects associated with Keflex are gastrointestinal in nature and may include diarrhea, nausea, vomiting, abdominal pain, and dyspepsia. Other reported adverse reactions include dizziness, fatigue, headache, genital pruritus, vaginitis, and transient elevations in hepatic enzymes. Allergic reactions can range from skin rashes, urticaria, and pruritus to more severe manifestations such as angioedema and anaphylaxis, though the latter is rare. As with nearly all broad-spectrum antibiotics, there is a risk of Clostridioides difficile-associated diarrhea (CDAD), which may range in severity from mild diarrhea to fatal colitis.

Drug interaction

Concomitant use of Keflex with probenecid may result in increased and prolonged blood levels of cephalexin due to decreased renal tubular secretion. The use of metformin with Keflex may increase metformin exposure and should be monitored. Although not well-documented, there is potential for interaction with other nephrotoxic drugs (e.g., aminoglycosides, potent diuretics) which may increase the risk of renal dysfunction. Close monitoring is advised when Keflex is administered with oral anticoagulants, as cephalosporins have been reported to potentiate anticoagulant effects, possibly by suppressing intestinal flora producing vitamin K.

Missed dose

If a dose of Keflex is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Doubling the dose to make up for a missed one is not recommended, as this may increase the risk of side effects.

Overdose

Symptoms of Keflex overdose may include nausea, vomiting, epigastric distress, diarrhea, and hematuria. In the event of a suspected overdose, symptomatic and supportive therapy should be instituted. Gastric lavage may be indicated if ingestion was recent. Cephalexin is eliminated primarily by the kidneys; therefore, maintaining adequate hydration and urinary output is important. Hemodialysis may aid in the removal of cephalexin from the body in cases of significant overdose, particularly in patients with renal impairment.

Storage

Keflex capsules and tablets should be stored at controlled room temperature, 20°C to 25°C (68°F to 77°F), in a tightly closed container, and protected from light and moisture. The oral suspension, once reconstituted, should be stored in a refrigerator (2°C to 8°C / 36°F to 46°F) and discarded after 14 days. Keep all medications out of the reach of children and pets.

Disclaimer

This information is for educational 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. The efficacy and safety of Keflex have not been established for all populations or all infections; use is at the discretion of a prescribing healthcare professional.

Reviews

(Compilation of simulated expert clinical perspectives based on established pharmacological data and treatment guidelines.)

“Keflex remains a workhorse in my practice for uncomplicated skin and soft tissue infections. Its predictable pharmacokinetics and generally favorable tolerability profile make it a reliable first-line choice for outpatient management.” – Infectious Disease Specialist, 15 years experience.

“In pediatric otitis media, weight-based dosing of cephalexin suspension provides effective coverage for the most common pathogens. I appreciate its palatability, which improves adherence in young children.” – Pediatrician, 10 years experience.

“For patients with a history of mild penicillin allergy (non-anaphylactic), cephalexin is often a suitable alternative after careful risk-benefit assessment. I have used it successfully in such cases for decades with a very low incidence of cross-reactivity.” – General Practitioner, 25 years experience.

“While its spectrum is not as broad as newer agents, the targeted activity of Keflex is an advantage in an era of antimicrobial stewardship. It allows for precise therapy, reducing the ecological pressure that drives resistance.” – Clinical Pharmacist, Hospital Formulary Committee.