Keflex (cephalexin) is a first-generation cephalosporin antibiotic prescribed for the treatment of a wide range of bacterial infections. It operates by interfering with the synthesis of the bacterial cell wall, leading to bacterial cell death. This medication is highly effective against susceptible strains of gram-positive and some gram-negative bacteria, making it a cornerstone in outpatient and inpatient therapeutic regimens. Its reliable bioavailability and established safety profile support its continued use in clinical practice for both adult and pediatric populations.

Features

• Active pharmaceutical ingredient: Cephalexin monohydrate
• Available in oral capsule strengths: 250 mg, 500 mg, and 750 mg
• Also available as an oral suspension: 125 mg/5 mL and 250 mg/5 mL
• Belongs to the beta-lactam antibiotic class, first-generation cephalosporin
• Demonstrates bactericidal activity by inhibiting cell wall synthesis
• Exhibits activity against Staphylococcus aureus (including penicillinase-producing strains), Streptococcus pneumoniae, Streptococcus pyogenes, Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae

Benefits

• Effectively treats common bacterial skin and soft tissue infections, including cellulitis and impetigo
• Provides reliable coverage for respiratory tract infections such as community-acquired pneumonia and streptococcal pharyngitis
• Offers a well-tolerated oral option for bone and joint infections caused by susceptible organisms
• Used for urinary tract infections, including acute uncomplicated cystitis and pyelonephritis
• Suitable for pediatric use with weight-based dosing and palatable suspension formulation
• Demonstrates a lower risk of cross-reactivity in patients with non-severe penicillin allergies compared to later-generation cephalosporins

Common use

Keflex is commonly prescribed for bacterial infections across multiple organ systems. In dermatology, it is frequently used for abscesses, wound infections, and folliculitis caused by Staphylococcus and Streptococcus species. For respiratory infections, it treats pharyngitis, tonsillitis, and bronchitis when bacterial etiology is confirmed. In urology, Keflex addresses cystitis, prostatitis, and other urinary tract infections caused by susceptible E. coli and Proteus species. Orthopedic applications include osteomyelitis treatment, particularly when caused by susceptible staphylococci. The medication also finds use in dental infections, including periodontal abscesses and post-procedural prophylaxis in high-risk patients.

Dosage and direction

Dosage must be individualized based on the infection’s severity, causative organism susceptibility, and patient renal function. For adults, the typical dosage ranges from 250 mg to 1 gram every 6 hours, with most infections responding to 500 mg every 12 hours. For children, the recommended dosage is 25-100 mg/kg/day divided into 2-4 doses, not to exceed 4 grams daily. The oral suspension should be shaken well before each administration. Keflex is best absorbed when taken on an empty stomach (1 hour before or 2 hours after meals), though it may be taken with food to minimize gastrointestinal upset. Complete the full prescribed course even if symptoms improve to prevent antibiotic resistance and ensure eradication of the infection.

Precautions

Patients should inform their healthcare provider of any history of gastrointestinal disease, particularly colitis, as antibiotic use can cause pseudomembranous colitis. Renal function should be assessed before initiation and monitored during therapy in patients with pre-existing renal impairment, as dosage adjustments are necessary. Use with caution in patients with a history of penicillin allergy due to potential cross-reactivity, though the risk is lower with first-generation cephalosporins. Prolonged use may result in fungal or bacterial superinfection, including oral thrush and vaginal candidiasis. Diabetic patients should be aware that cephalexin may cause false-positive urine glucose tests when using copper reduction methods.

Contraindications

Keflex is contraindicated in patients with known hypersensitivity to cephalexin or any component of the formulation. It is also contraindicated in patients with a history of anaphylactic reaction to penicillins or other beta-lactam antibiotics due to potential cross-reactivity. The medication should not be used for the treatment of viral infections, including the common cold or influenza, as antibiotics are ineffective against viruses. Contraindicated in patients with a history of antibiotic-associated colitis or pseudomembranous colitis. Not recommended for the treatment of meningitis as it does not achieve adequate cerebrospinal fluid concentrations.

Possible side effect

The most commonly reported adverse effects involve the gastrointestinal system, including diarrhea (occurring in up to 10% of patients), nausea, vomiting, abdominal pain, and dyspepsia. Dermatological reactions may include rash, urticaria, and pruritus. Genitourinary side effects can include vaginitis and genital pruritus. Less frequently, patients may experience dizziness, fatigue, headache, or joint pain. Serious but rare side effects include pseudomembranous colitis (characterized by severe diarrhea), Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatitis, and reversible interstitial nephritis. Hematological effects may include eosinophilia, neutropenia, thrombocytopenia, and rarely, hemolytic anemia.

Drug interaction

Probenecid may decrease the renal tubular secretion of cephalexin, resulting in increased and prolonged blood levels. Concomitant use with bacteriostatic antibiotics (e.g., tetracyclines, erythromycin) may antagonize the bactericidal effect of cephalexin. Metformin concentrations may increase when co-administered with cephalexin, potentially enhancing its hypoglycemic effect. Oral contraceptives may have reduced efficacy during cephalexin therapy; additional non-hormonal contraception is recommended. Warfarin’s anticoagulant effect may be enhanced, requiring more frequent INR monitoring. Concomitant use with other nephrotoxic drugs (aminoglycosides, loop diuretics) may increase the risk of renal toxicity.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next scheduled dose. In that case, skip the missed dose and resume the regular dosing schedule. Do not double the dose to make up for a missed administration. Maintaining consistent antibiotic blood levels is important for therapeutic efficacy, so patients should strive to adhere to the prescribed dosing interval. Setting reminders or using pill organizers can help maintain dosing regularity throughout the treatment course.

Overdose

Cephalexin overdose may manifest as nausea, vomiting, epigastric distress, diarrhea, and hematuria. In cases of significant overdose, particularly in patients with renal impairment, neurotoxicity including seizures may occur. Management is primarily supportive and symptomatic. Gastric lavage may be considered if ingestion was recent. Hemodialysis may be effective in removing cephalexin from the bloodstream, particularly in patients with renal compromise. Serum electrolyte levels and renal function should be monitored. There is no specific antidote for cephalexin overdose.

Storage

Store capsules and tablets at room temperature (15-30°C or 59-86°F) in a tightly closed container, protected from light and moisture. Keep the oral suspension refrigerated (2-8°C or 36-46°F) after reconstitution; discard any unused portion after 14 days. Do not freeze the suspension. Keep all medications out of reach of children and pets. Do not store in bathroom cabinets where humidity and temperature fluctuations may degrade the medication. Do not use beyond the expiration date printed on the packaging.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting, changing, or stopping any medication. The prescribing physician should be aware of the patient’s complete medical history, current medications, and allergies. Dosage and treatment duration should be determined by a healthcare provider based on the specific infection, pathogen susceptibility, and patient factors. Never share prescription medications with others, even if they have similar symptoms.

Reviews

Clinical studies and decades of use demonstrate Keflex’s efficacy in treating susceptible bacterial infections. In dermatological applications, success rates exceed 85% for uncomplicated skin and soft tissue infections. For respiratory tract infections, clinical cure rates range from 80-90% for streptococcal pharyngitis and community-acquired pneumonia. Urological applications show bacteriologic cure rates of 75-85% for uncomplicated urinary tract infections. The medication is generally well-tolerated, with most adverse effects being mild and self-limiting. Healthcare providers appreciate its predictable pharmacokinetics, multiple formulation options, and established place in therapy across patient populations.