What it's for (Indications)
- Cephalexin is indicated for the treatment of infections caused by susceptible strains of microorganisms.
- Common indications include respiratory tract infections, such as pharyngitis, tonsillitis, and sinusitis, skin and skin structure infections, including cellulitis, abscesses, and furunculosis, and urinary tract infections, such as cystitis and pyelonephritis, when caused by susceptible Gram-positive and some Gram-negative bacteria.
- It is also used in the management of otitis media, bone and joint infections, and dental infections.
- Before initiating treatment, appropriate susceptibility testing should be performed to confirm the efficacy of cephalexin against the causative pathogen.
- The selection of cephalexin should always consider local epidemiological patterns of bacterial resistance and official treatment guidelines to ensure optimal patient outcomes and minimize the development of antimicrobial resistance.
- Its broad spectrum against common community-acquired pathogens makes it a frequently prescribed oral antibiotic, especially when Gram-positive coverage is a priority.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | The dosage of cephalexin varies significantly depending on the severity and type of infection, the patient's age, weight, renal function, and the specific formulation (e.g., capsules, oral suspension). For adults, typical oral doses range from 250 mg to 500 mg every 6 to 12 hours. For children, the recommended dosage is usually based on body weight, commonly 25 to 50 mg/kg/day, administered in divided doses. In more severe infections, the dosage may be increased. For example, some severe infections might require up to 100 mg/kg/day for pediatric patients or up to 4 grams per day for adults, divided into multiple doses. It is crucial to complete the full prescribed course of therapy, even if symptoms improve, to prevent relapse and the development of antibiotic resistance. Dosage adjustments are necessary for patients with impaired renal function, and monitoring of kidney function may be advisable. Healthcare professionals should always refer to the specific product monograph and clinical guidelines for precise dosing instructions, particularly for pediatric dosing where the 'Keflex 60 ml Suspension' would be relevant. |
Safety & Warnings
Common Side Effects
- As with most antibiotics, cephalexin can cause various side effects, although many are mild and transient.
- The most commonly reported adverse reactions involve the gastrointestinal system and include nausea, vomiting, diarrhea, abdominal pain, and dyspepsia.
- Hypersensitivity reactions are also possible, ranging from mild rashes, urticaria, and pruritus to more severe manifestations such as angioedema, anaphylaxis, and Stevens-Johnson syndrome, necessitating immediate medical attention.
- Other potential side effects include dizziness, headache, fatigue, candidiasis (oral or vaginal thrush), and transient elevations in liver enzymes.
- Rarely, more serious adverse events like Clostridioides difficile-associated diarrhea (CDAD), pseudomembranous colitis, neutropenia, eosinophilia, thrombocytopenia, and renal impairment have been reported.
- Patients should be advised to seek immediate medical attention if they experience signs of a severe allergic reaction or persistent, severe diarrhea.
- Comprehensive patient counseling regarding potential side effects is essential to ensure patient safety and adherence to treatment.
Serious Warnings
- Black Box Warning: Cephalexin does not carry a formal FDA Black Box Warning. However, several serious warnings and precautions are critical for safe and effective use. Severe and occasionally fatal hypersensitivity reactions, including anaphylaxis, have been reported with cephalosporin antibiotics, including cephalexin. Prior to initiating therapy, careful inquiry must be made regarding previous hypersensitivity reactions to cephalexin, other cephalosporins, penicillins, or other allergens. If an allergic reaction occurs, cephalexin must be discontinued immediately, and appropriate emergency treatment administered. Additionally, *Clostridioides difficile*-associated diarrhea (CDAD) has been reported with nearly all antibacterial agents, including cephalexin, and can range from mild diarrhea to fatal colitis. This must be considered in all patients who present with diarrhea following antibiotic use. Cephalexin is primarily eliminated by the kidneys; therefore, dosage adjustments are necessary in patients with impaired renal function to prevent drug accumulation and potential adverse effects. Renal function should be closely monitored in these individuals. While the risk of cross-reactivity with penicillin is low, patients with a documented history of severe penicillin allergy should be treated with extreme caution, and alternative antimicrobial agents should be considered if appropriate.
- Several critical warnings and precautions are associated with cephalexin use.
- Patients with a history of hypersensitivity to cephalexin or other cephalosporins, penicillins, or other beta-lactam antibiotics are at increased risk of allergic reactions and should be carefully evaluated; cross-reactivity between penicillins and cephalosporins has been documented and can be severe.
- Cephalexin should be used with caution in individuals with a history of gastrointestinal disease, particularly colitis, as antibiotic-associated colitis, including Clostridioides difficile-associated diarrhea (CDAD), can occur and range in severity from mild to life-threatening.
- Prolonged use of cephalexin may result in the overgrowth of non-susceptible organisms, necessitating careful monitoring for superinfection, such as fungal infections.
- Renal function should be assessed in patients with pre-existing renal impairment, and dosage adjustments may be required to prevent drug accumulation and potential toxicity.
- Furthermore, cephalexin can interfere with certain laboratory tests, such as false-positive results for urinary glucose using copper reduction tests (e.
- g.
- , Benedict's or Fehling's solution) and a false-positive direct Coombs' test.
- Pregnant and lactating individuals should use this medication only if clearly needed, with careful consideration of the risk-benefit profile for both mother and child.
How it Works (Mechanism of Action)
Cephalexin, a first-generation cephalosporin antibiotic, exerts its bactericidal effects by interfering with the synthesis of the bacterial cell wall. Its primary mechanism involves the inhibition of penicillin-binding proteins (PBPs), which are enzymes located in the bacterial cytoplasmic membrane. These PBPs play a crucial role in the final stages of peptidoglycan synthesis, particularly in the transpeptidation reaction, which is essential for cross-linking the peptidoglycan strands to form a stable and rigid cell wall. The beta-lactam ring structure of cephalexin irreversibly binds to and acylates the active site of these PBPs, effectively inactivating them. This covalent binding prevents the crucial cross-linking process, leading to the formation of a defective and osmotically unstable cell wall. Consequently, the bacterial cell loses its structural integrity, resulting in cell lysis and ultimately bacterial death. This action is characteristic of beta-lactam antibiotics, making cephalexin a potent agent against susceptible bacteria, particularly those Gram-positive organisms that rely heavily on peptidoglycan for structural integrity.