Cephalexin is a first-generation cephalosporin antibiotic available as a generic medication and marketed under brand names such as Keflex. It belongs to the Antibiotics therapeutic class and is supplied in pill form, most commonly at a strength of 500 mg per tablet. In Hong Kong, cephalexin is a prescription-only (Rx) product regulated by the Department of Health. It is used to treat a variety of bacterial infections by inhibiting bacterial cell-wall synthesis.
Cephalexin interferes with the construction of bacterial cell walls. It binds to penicillin-binding proteins (PBPs), which are enzymes essential for cross-linking peptidoglycan strands. By blocking these enzymes, cephalexin weakens the cell wall, leading to bacterial lysis and death.
Because cephalexin is a β-lactam, it is primarily eliminated unchanged by the kidneys, making renal function an important consideration for dosing.
Cephalexin is approved for the treatment of a range of bacterial infections that are susceptible to first-generation cephalosporins. In Hong Kong, the Department of Health lists the following approved indications:
These uses reflect the drug’s activity against common Gram-positive organisms (Staphylococcus aureus, Streptococcus pneumoniae) and some Gram-negative bacteria (Escherichia coli, Klebsiella species).
Absolute contraindications
Known hypersensitivity to cephalexin, other cephalosporins, or penicillins.
History of serious allergic reactions (e.g., anaphylaxis) to any β-lactam antibiotic.
Relative contraindications
Severe renal impairment (creatinine clearance < 30 mL/min) without dose adjustment.
Pregnancy or lactation: cephalexin is generally considered safe, but it should be used only when clearly needed.
Certain gastrointestinal diseases (e.g., colitis) that may be aggravated by broad-spectrum antibiotics.
These effects are usually mild and resolve without intervention. If a rash becomes widespread or is accompanied by fever, seek medical attention as it may signal a more serious reaction.
If you are taking other prescription or over-the-counter products, inform your healthcare provider before starting cephalexin.
The exact dose and duration depend on the infection type, severity, and patient factors. Typical courses range from 5 days (for uncomplicated skin infections) to 10-14 days (for bone or urinary tract infections).
If you miss a dose, take it as soon as you remember unless it is near the time of the next scheduled dose. Do not double the dose.
Complete the prescribed course even if symptoms improve, to prevent relapse and resistance. If a serious adverse reaction occurs, a physician may advise abrupt cessation and provide alternative therapy.
Regular follow-up with a healthcare professional ensures the infection resolves and helps identify any emerging side effects.
This article provides educational information about cephalexin and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
Cephalexin does not have a known effect on hormonal contraceptives, so it is generally considered safe to use together. However, if you experience persistent vomiting or diarrhea, discuss backup contraception with your healthcare provider.
A mild rash may resolve on its own, but any skin eruption that spreads, is accompanied by fever, or looks like hives warrants immediate medical evaluation for a possible allergic reaction.
Yes, but keep the medication in its original labeled container, carry a copy of the prescription, and be aware of local regulations regarding antibiotics. Some countries may require documentation for import.
Both are effective against many streptococcal strains, but cephalexin is often preferred when the infecting organism is known to produce β-lactamase, as it is more resistant to this enzyme. Choice depends on the clinician’s assessment of the likely pathogen.
Crushing is not recommended for the standard tablet formulation because it may affect absorption. If swallowing is an issue, ask your pharmacist about an appropriate liquid preparation.
The 500 mg tablet provides a convenient dose that aligns with common adult regimens (e.g., 500 mg every 6 hours). It allows flexibility for both moderate and more severe infections without needing multiple tablets per dose.
Broad-spectrum antibiotics can disrupt normal bacterial flora, sometimes leading to overgrowth of yeast, especially in women. If you notice symptoms such as itching or discharge, discuss treatment options with your clinician.
Cephalexin’s absorption is not significantly affected by calcium or dairy, so you do not need to separate the dose from meals containing milk or cheese.
The drug’s half-life is about 1 hour in individuals with normal renal function, meaning it is mostly eliminated within 5-6 hours. In patients with impaired kidneys, clearance may be prolonged.
Cephalexin is not known to interfere with standard workplace or sports drug-testing panels. Nonetheless, always disclose all medications to testing authorities if required.
