Absorption Rate Constant (Ka)

The first-order rate constant (Ka) describing the rate at which a drug is absorbed from the site of administration into systemic circulation. Higher Ka indicates faster absorption, while lower Ka may result in sustained drug levels. Ka is a critical parameter in compartmental pharmacokinetic modeling and determines the shape of the plasma concentration-time curve during the absorption phase.

Exemplos

• Rapid Ka: sublingual nitroglycerin (~0.1 min absorption)
• Slow Ka: sustained-release morphine formulations
• Ka estimation via Wagner-Nelson method or deconvolution