From the package insert[1] : The half-life of Amoxicillin is 61.3 minutes. Approximately 60% of an orally administered dose of Amoxicillin is excreted in the urine within 6 to 8 hours. Detectable serum levels are observed up to 8 hours after an orally administered dose of Amoxicillin. Most antibiotics have somewhat longer half-lives, on the order of 3-4 hours.