Cephalexin's half-life typically ranges from 45 to 120 minutes, significantly increasing with impaired kidney function.
After a 250mg dose, less than 1mg of the drug would likely remain in the body after approximately 3 hours in individuals with normal kidney function.
Remember, these are general estimates, and individual variations may occur. Always follow your doctor's specific instructions for taking cephalexin and consult them if you have any questions about its duration of action or potential interactions with other medications
Cephalexin Half-Life and Duration of Activity
Cephalexin, a first-generation cephalosporin antibiotic, has a pharmacokinetic profile heavily influenced by kidney function. Its elimination half-life, the time it takes for half the drug to be eliminated from the body, varies depending on the source:
Normal renal function: Most resources cite a half-life of around 60 minutes, with some sources ranging from 45 to 120 minutes. (e.g., StatPearls, Drugs.com)
Impaired renal function: As kidney function declines, the half-life significantly increases. For instance, patients with moderate renal impairment might have a half-life of 3-4 hours, while those with severe impairment could reach 8-12 hours or even longer. (e.g., Cephalexin 500mg Tablets - Summary of Product Characteristics)
Estimating Cephalexin Duration of Action:
Based on the typical half-life of 60 minutes, after one 250mg dose:
50% of the drug would be eliminated after 60 minutes.
25% would remain after another 60 minutes (120 minutes total).
12.5% (approx. 3mg) would remain after another 60 minutes (180 minutes total).
Therefore, under normal kidney function, you could expect less than 1mg of cephalexin to remain in the body approximately 3 hours after a single 250mg dose.
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