Usage
Cefalexin is a first-generation cephalosporin antibiotic prescribed for various bacterial infections. It is effective against gram-positive bacteria like Streptococcus pneumoniae and Staphylococcus aureus and some gram-negative bacteria like Escherichia coli and Klebsiella pneumoniae.
Its pharmacological classification is antibiotic.
Cefalexin’s mechanism of action involves inhibiting bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs). This leads to cell wall instability and bacterial lysis (death).
Alternate Names
Cefalexin is also known internationally as Cephalexin. Brand names include Keflex, Keftab, and others. Always check local formularies for available formulations and brand names.
How It Works
Pharmacodynamics: Cefalexin exerts its bactericidal effect by disrupting bacterial cell wall synthesis. Specifically, it binds to PBPs, enzymes essential for cross-linking peptidoglycans, the building blocks of bacterial cell walls. This weakens the cell wall, ultimately leading to bacterial cell death.
Pharmacokinetics:
- Absorption: Cefalexin is well-absorbed orally. Food may slightly delay but does not significantly reduce absorption.
- Metabolism: Minimally metabolized in the liver.
- Elimination: Primarily excreted unchanged in the urine via glomerular filtration and tubular secretion. Elimination half-life is around 1 hour, which may increase with renal insufficiency.
Mode of Action: Cefalexin’s mode of action is primarily through inhibition of bacterial cell wall synthesis. It binds to specific PBPs within the bacterial cell wall, preventing peptidoglycan cross-linking and ultimately leading to bacterial cell lysis.
Elimination Pathways: Primarily excreted unchanged through renal excretion.
Dosage
Standard Dosage
Adults:
- Standard dose: 250 mg to 500 mg orally every 6 to 12 hours.
- Maximum daily dose: Up to 4 grams, although parenteral administration might be preferred for doses exceeding this amount.
Children:
- Dose: 25-50 mg/kg/day orally, divided every 6 to 12 hours for mild to moderate infections. Dosages up to 100 mg/kg/day may be used for more severe infections.
- Pediatric safety: Generally well-tolerated in children. Monitor for adverse reactions like diarrhea and allergic reactions.
Special Cases:
- Elderly Patients: Dose adjustment usually not required unless significant renal impairment exists.
- Patients with Renal Impairment: Dosage adjustment based on creatinine clearance is crucial.
- Patients with Hepatic Dysfunction: No dosage adjustments are typically needed.
- Patients with Comorbid Conditions: Use with caution in patients with seizure disorders, as high doses can lower seizure threshold, especially in patients with renal impairment.
Clinical Use Cases
Specific dosage recommendations should be tailored based on infection severity, patient condition, and local treatment guidelines. However, cefalexin isn’t indicated for the clinical scenarios mentioned (Intubation, Surgical Procedures, Mechanical Ventilation, Intensive Care Unit (ICU) Use, Emergency Situations). It primarily covers gram-positive infections and some specific gram-negative infections. Consult specific guidelines for antibiotic prophylaxis or treatment in these settings.
Dosage Adjustments
- Renal Dysfunction: Dosage reduction required based on creatinine clearance. Refer to guidelines for specific adjustments.
- Hepatic Dysfunction: No adjustment usually necessary.
Side Effects
Common Side Effects:
- Diarrhea
- Nausea
- Vomiting
- Indigestion
- Abdominal pain
Rare but Serious Side Effects:
- Allergic reactions (rash, hives, itching, swelling, difficulty breathing)
- Clostridium difficile-associated diarrhea (pseudomembranous colitis)
- Seizures (particularly with high doses or renal impairment)
- Serum sickness-like reaction
- Stevens-Johnson syndrome
Long-Term Effects:
- Potential for C. difficile overgrowth and superinfection with prolonged use.
- Vitamin K deficiency (rare).
Adverse Drug Reactions (ADR):
- Anaphylaxis (rare but potentially life-threatening)
- Toxic epidermal necrolysis (rare).
Contraindications
- Hypersensitivity to cefalexin or other cephalosporins.
- History of severe allergic reaction to penicillins (cross-reactivity risk).
Drug Interactions
- Probenecid: Reduces renal excretion of cefalexin, increasing serum levels.
- Metformin: Cefalexin may increase metformin levels, increasing the risk of lactic acidosis.
- Anticoagulants (e.g., warfarin): Monitor INR closely, as cefalexin might potentiate anticoagulant effects.
- Oral contraceptives: Effectiveness may be reduced; advise patients to use alternative contraception.
Pregnancy and Breastfeeding
- Pregnancy: Generally considered safe (Pregnancy Category B). However, always weigh the benefits against potential risks.
- Breastfeeding: Small amounts are excreted in breast milk. Monitor the infant for diarrhea or thrush.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial cell wall synthesis by binding to PBPs.
- Side Effects: Diarrhea, nausea, vomiting, allergic reactions.
- Contraindications: Hypersensitivity to cephalosporins or severe penicillin allergy.
- Drug Interactions: Probenecid, metformin, warfarin, oral contraceptives.
- Pregnancy & Breastfeeding: Generally safe, but use with caution.
- Dosage: Refer to detailed dosage guidelines above.
- Monitoring Parameters: Renal function (especially in patients with pre-existing renal disease), signs of superinfection, resolution of infection symptoms.
Popular Combinations
Cefalexin is generally used as monotherapy. Combinations are not routine and require careful consideration.
Precautions
- General Precautions: Assess for allergies, renal function, and potential drug interactions.
- Specific Populations: Standard precautions apply to pregnant/breastfeeding women, children, and the elderly based on dose adjustments.
- Lifestyle Considerations: Alcohol does not significantly interact with cefalexin. No specific dietary restrictions are usually needed.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Cefalexin?
A: The dosage varies depending on the age of the patient, the severity of the infection, and renal function. See the “Dosage” section for a detailed breakdown.
Q2: What are the common side effects of Cefalexin?
A: Common side effects include diarrhea, nausea, vomiting, abdominal pain, and indigestion.
Q3: Is Cefalexin safe to use during pregnancy and breastfeeding?
A: Generally considered safe for use during both pregnancy and breastfeeding, but clinical judgment is essential.
Q4: What are the contraindications for using Cefalexin?
A: Contraindications include hypersensitivity to cefalexin or other cephalosporins, and a history of severe penicillin allergy.
Q5: How does Cefalexin work?
A: Cefalexin inhibits bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs).
Q6: Does food affect the absorption of Cefalexin?
A: Food may slightly delay absorption but does not significantly impact bioavailability.
Q7: How should Cefalexin be administered?
A: Cefalexin is typically administered orally as capsules, tablets, or suspension.
Q8: What are the signs of a severe allergic reaction to Cefalexin?
A: Signs of a severe allergic reaction may include difficulty breathing, swelling of the face, lips, or tongue, hives, and a rapid heartbeat. Seek immediate medical attention if these occur.
Q9: How long should a course of Cefalexin typically last?
A: The duration of Cefalexin treatment is generally 7 to 14 days, depending on the infection and the patient’s response to treatment. For beta-haemolytic streptococcal infections, a minimum of 10 days is recommended.
