Keflex: Effective First-Line Cephalosporin Antibiotic Therapy
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Keflex, known generically as cephalexin, is a first-generation cephalosporin antibiotic prescribed for the treatment of a wide range of bacterial infections. It operates by interfering with the bacteria’s cell wall synthesis, leading to osmotic instability and cell death. This oral medication is a cornerstone in outpatient management due to its reliable bioavailability and broad-spectrum activity against many Gram-positive and some Gram-negative pathogens. Its established efficacy and favorable safety profile make it a frequently selected agent for both adult and pediatric populations in appropriate clinical scenarios.
Features
- Active pharmaceutical ingredient: Cephalexin monohydrate
- Available in oral formulations: 250 mg, 500 mg, and 750 mg capsules; 125 mg/5 mL and 250 mg/5 mL oral suspensions
- Pharmacologic class: First-generation cephalosporin antibiotic
- Mechanism of action: Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs)
- Spectrum of activity: Effective against many Gram-positive cocci (including penicillin-susceptible Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae) and some Gram-negative bacteria (e.g., Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae)
- Bioavailability: Well-absorbed from the gastrointestinal tract, with peak serum concentrations achieved within 1 hour
- Half-life: Approximately 0.5–1.2 hours in adults with normal renal function
- Excretion: Primarily renal, with approximately 80–100% excreted unchanged in urine within 8 hours
Benefits
- Provides rapid bactericidal action against susceptible pathogens, facilitating prompt clinical improvement.
- Offers high oral bioavailability, ensuring effective systemic concentrations without the need for intravenous administration in many cases.
- Demonstrates a well-documented efficacy profile for common community-acquired infections, supporting evidence-based prescribing.
- Features a generally favorable tolerability profile, with most adverse effects being mild and self-limiting.
- Available in multiple dosage forms and strengths, allowing for precise dosing across different age groups and clinical indications.
- Serves as a suitable alternative for patients with non-anaphylactic penicillin allergies, following appropriate clinical assessment.
Common use
Keflex is indicated for the treatment of bacterial infections caused by susceptible strains of designated microorganisms. Common clinical applications include:
- Respiratory tract infections (e.g., pharyngitis, tonsillitis, bronchitis, and community-acquired pneumonia caused by susceptible Streptococcus pneumoniae and Streptococcus pyogenes)
- Skin and skin structure infections, including cellulitis, abscesses, and wound infections, particularly those caused by Staphylococcus aureus (including penicillinase-producing strains) and Streptococcus pyogenes
- Bone infections (osteomyelitis) caused by Staphylococcus aureus and/or Proteus mirabilis
- Genitourinary tract infections, such as acute and chronic prostatitis, cystitis, and pyelonephritis, primarily due to Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae
- Otitis media caused by Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Streptococcus pyogenes, and Moraxella catarrhalis
It is imperative that therapy is directed only against pathogens demonstrated to be susceptible by culture and sensitivity testing, or, when such data are not available, against pathogens known to be commonly susceptible based on epidemiological and microbiological patterns.
Dosage and direction
The dosage of Keflex must be individualized based on the infection’s severity, the causative organism’s susceptibility, and the patient’s renal function.
Adults: The usual adult dose is 250 mg every 6 hours, or 500 mg every 12 hours. For more severe infections, doses may be increased to 500 mg every 6 hours or 1 gram every 12 hours. The maximum daily dose for adults is 4 grams.
Pediatric Patients: The recommended total daily dose for children is 25 to 50 mg/kg/day divided into two or four equal doses. For otitis media, the recommended dose is 75 to 100 mg/kg/day divided into four doses. The maximum daily dose for children should not exceed 4 grams.
Patients with Renal Impairment: Dosage adjustments are necessary. For patients with a creatinine clearance of 10-50 mL/min, the dosing interval should be extended to every 12-24 hours. For patients with a creatinine clearance of less than 10 mL/min, the dosing interval should be extended to every 24-48 hours. Hemodialysis patients should receive a supplementary dose following dialysis.
Administration: Keflex capsules should be swallowed whole with a full glass of water. The oral suspension must be shaken vigorously before each administration to ensure uniform dosing. It can be taken with or without food; however, administration with food may minimize potential gastrointestinal upset. The entire prescribed course must be completed, even if symptoms resolve earlier, to prevent the development of antibiotic resistance.
Precautions
- General: Prescribe with caution to patients with a history of gastrointestinal disease, particularly colitis, as antibiotic use is associated with Clostridium difficile-associated diarrhea (CDAD).
- Renal Impairment: Since Keflex is primarily excreted by the kidneys, careful clinical observation and appropriate dosage adjustments are mandatory in patients with impaired renal function to prevent drug accumulation and potential toxicity.
- Superinfection: Use may result in overgrowth of nonsusceptible organisms, including fungi. Constant observation of the patient is essential. If superinfection occurs during therapy, appropriate measures should be taken.
- Phenylketonurics: The oral suspension contains aspartame, which is metabolized to phenylalanine. This must be considered when administering to patients with phenylketonuria (PKU).
- Laboratory Tests: In patients receiving prolonged therapy, periodic assessment of renal, hepatic, and hematopoietic function is advisable.
- Drug Resistance: To reduce the development of drug-resistant bacteria and maintain the effectiveness of Keflex and other antibacterial drugs, this drug should be used only to treat or prevent infections proven or strongly suspected to be caused by susceptible bacteria.
Contraindications
Keflex is contraindicated in patients with known hypersensitivity to cephalexin or any other cephalosporin antibiotic. A thorough patient history concerning previous hypersensitivity reactions to cephalosporins, penicillins, or other drugs must be obtained before initiating therapy. Cross-hypersensitivity among beta-lactam antibiotics has been well-documented; therefore, Keflex should be administered with extreme caution to any patient who has demonstrated some form of allergy, particularly to drugs.
Possible side effect
As with all pharmacological agents, Keflex can cause adverse reactions. The most common side effects involve the gastrointestinal system and are generally mild and transient.
- Gastrointestinal: Diarrhea, nausea, vomiting, dyspepsia, abdominal pain, and anorexia have been reported. Clostridium difficile-associated diarrhea (CDAD) has been reported with nearly all antibacterial agents and may range in severity from mild diarrhea to fatal colitis.
- Hypersensitivity Reactions: Maculopapular rash, urticaria, pruritus, and drug fever have been observed. These reactions may necessitate discontinuation of therapy. Serious acute hypersensitivity reactions, including anaphylaxis, though rare, have been reported.
- Central Nervous System: Dizziness, fatigue, headache, and confusion have occurred, particularly in elderly patients or those with renal impairment.
- Hepatic: Transient elevations in hepatic enzymes (AST, ALT, alkaline phosphatase) and jaundice have been reported.
- Renal: Reversible interstitial nephritis has been rarely reported.
- Hematologic: Eosinophilia, neutropenia, thrombocytopenia, and slight elevations in prothrombin time have been observed.
- Other: Genital pruritus, vaginitis, and candidiasis.
Patients should be advised to report any severe or persistent side effects to their healthcare provider immediately.
Drug interaction
Concurrent administration of Keflex with other medications may alter its effectiveness or increase the risk of adverse reactions.
- Probenecid: Coadministration with probenecid may result in increased and prolonged blood levels of cephalexin by competitively inhibiting renal tubular secretion.
- Metformin: Cephalexin may increase the serum concentration of metformin. Close monitoring of blood glucose and metformin-related side effects is recommended.
- Oral Anticoagulants (Warfarin): There are postmarketing reports of increased prothrombin time with concomitant use of cephalosporins and warfarin. Monitoring of prothrombin time or INR is advisable.
- Nephrotoxic Drugs: Concurrent use of Keflex with potent diuretics (e.g., furosemide, ethacrynic acid) or other nephrotoxic agents (e.g., aminoglycosides, polymyxins) may increase the potential for nephrotoxicity. Renal function should be carefully monitored.
- Bacteriostatic Antibiotics (e.g., tetracyclines, erythromycin): The bactericidal action of cephalexin may be antagonized by bacteriostatic antibiotics. This combination should be avoided unless deemed necessary.
A comprehensive review of the patient’s complete medication regimen, including prescription, over-the-counter, and herbal products, is essential before initiating therapy.
Missed dose
If a dose 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. Patients should be instructed not to double the dose to make up for a missed one, as this increases the risk of adverse effects. Maintenance of a consistent serum concentration is important for efficacy, so patients should be encouraged to adhere strictly to the prescribed dosing schedule.
Overdose
Symptoms of overdose are primarily extensions of the drug’s adverse effects and may include nausea, vomiting, epigastric distress, diarrhea, and hematuria. In the event of a suspected overdose, symptomatic and supportive care is the mainstay of treatment. Gastric lavage may be considered if ingestion was recent. Keflex is eliminated by hemodialysis; this may be employed in cases of significant overdose, particularly in patients with renal impairment. Management should include maintenance of glomerular filtration rate and careful monitoring of renal, hepatic, and hematopoietic function.
Storage
Keflex capsules 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 between 2°C and 8°C (36°F and 46°F) and discarded after 14 days. Keep all medications out of the reach of children and pets. Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Proper disposal through a medicine take-back program is the preferred method.
Disclaimer
This information is intended 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. The content has been compiled from various sources believed to be accurate and reliable at the time of writing; however, no warranty, express or implied, is made regarding accuracy, adequacy, completeness, legality, reliability, or usefulness of any information.
Reviews
Clinical efficacy and patient feedback consistently affirm Keflex’s role as a reliable oral antibiotic. In clinical studies, it has demonstrated high success rates in eradicating susceptible pathogens across its indicated uses. Patient-reported outcomes often cite a rapid resolution of symptoms, such as reduced fever, diminished pain, and improved overall well-being, typically within 48-72 hours of initiating therapy. The tolerability profile is generally rated favorably, with most adverse effects being mild gastrointestinal disturbances that seldom require discontinuation. Healthcare professionals value its predictable pharmacokinetics, multiple formulation options for precise dosing, and its established position in treatment guidelines for common community-acquired infections. Its utility as an alternative for patients with non-severe penicillin allergies is frequently highlighted in clinical practice. As with all antibiotics, the necessity for susceptibility testing and appropriate duration of therapy to combat resistance is a recurring theme in expert reviews.