Why is Cephalexin prescribed every 8 hours?

Cephalexin is prescribed every 8 hours primarily due to its half-life. The half-life of a medication is the time it takes for the concentration of the drug in the bloodstream to reduce by half. For cephalexin, this half-life is relatively short, typically around 1 hour. To maintain effective therapeutic levels and ensure adequate antibacterial activity throughout the dosing interval, it is necessary to dose the medication frequently, in this case, every 8 hours. This frequency helps to avoid potential subtherapeutic levels that could compromise the treatment of the infection, while also reducing the risk of resistance developing due to inadequate drug levels in the body.

The other choices do not directly relate to the pharmacokinetics of cephalexin and its dosing schedule. Cost does not influence dosing frequency, and cephalexin is not classified as a controlled substance, which means the regulations surrounding its prescription differ from those of controlled drugs. Patient tolerance considerations may be relevant to the overall treatment plan but are not a primary reason for the specific dosing schedule based on the pharmacokinetic properties of the drug.