Cefalexin

Oral Antibiotics

Drug class: First-Generation Cephalosporin Antibiotic

Cefalexin (KEFLEX)（中文：頭孢氨芐）

Common Strengths of Cefalexin

Cefalexin is available in several strengths including:

• 125 mg
• 250 mg
• 500 mg

Drug Tarde Name of Cefalexin

Cefalexin is marketed under various trade names, including:

• Keflex

Drug Usage

Cefalexin is used to treat bacterial infections such as:

• Respiratory tract infections
• Otitis media (ear infections)
• Skin and soft tissue infections
• Bone and joint infections
• Urinary tract infections (UTIs)
• Dental infections

It is not effective against viral infections or certain resistant bacteria like MRSA.

Mechanism of Action

Cefalexin works by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs), disrupting the peptidoglycan layer, which is essential for bacterial cell wall integrity, leading to cell lysis and death.

Route of Administration

Oral

Dosages

• Normal aadults: 250 mg to 500 mg every 6 to 12 hours.
• Renal Dose: For eGFR <60 mL/min, the maximum daily dose should not exceed 1000 mg.

Side Effects

Frequency	Adverse reactions
Common Side Effects	Nausea
	Diarrhea
	Stomach pain
	Rash
	Dizziness
Serious Side Effects	Severe allergic reactions (anaphylaxis)
	Clostridium difficile infection (severe diarrgea)
	Liver dysfunction (yellowing of skin/eyes)
	Nephrotoxicity in patients with renal impairment

Pharmacokinetics

• Onset of Action: Typically, within 1 hour.
• Duration: Therapeutic levels maintained for 6 to 8 hours.
• Half-life: Approximately 1 hour in individuals with normal renal function.

Drug Precautions

Pregnancy

Cefalexin is generally considered safe during pregnancy, but it should only be used if clearly needed.

Breastfeeding

Cefalexin is excreted in breast milk in small amounts; it is usually deemed safe but should be used with caution.

Children and Elderly

Cefalexin can be used in children and the elderly, with dosage adjustments based on weight and renal function.

Monitoring Requirements

Regular monitoring of renal function is recommended, especially in patients with pre-existing conditions or those on other nephrotoxic medications.

Drug Interactions

Cefalexin may interact with:

• Warfarin: Cefalexin can enhance the anticogulant effect of warfarin, increasing the risk of bleeding.
• Metformin: The combination may increase metformin levels, leading to a higher risk of lactic aicdosis.
• Furosemide (Lasix): Co-administration can impair kidney function, so renal function should be monitored.
• Aminoglycosides: Using cephalexin with aminoglycoside antibiotics raises the risk of nephrotoxicty, necessitating careful monitoring of kidney function.
• Probenecid: This gout medication can increase cefalexin levels in blood, potentially enhancing side effects
• Caffeine: May exacerbate gastrointestinal side effects when taken with cefalexin.
• Zinc Supplements: Zinc can reduce the absorption of cefalexin; it's advosable tp space their intake by at least three hours.

FAQ

How Should I Take the Tablet?

Swallow cefalexin tablets whole with a glass of water. Do not chew or break them. It can be taken with or without food.

What Should I Avoid While Taking?

Avoid alcohol, as it may exacerbate side effects like nausea.

What Happens if I Miss a Dose?

Take the missed dose as soon as you remember, but skip it if it is almost time for your next dose. Do not double up on doses.