Explain the key pharmacokinetic (PK) and pharmacodynamic (PD) parameters for biologics.

Pharmacokinetics (what body does to drug) parameters: Cmax (peak concentration), Tmax (time to peak), AUC (area under curve, total exposure), half-life (t1/2, time for 50% elimination - longer for antibodies, ~21 days due to FcRn recycling), clearance (volume cleared per time), and volume of distribution (apparent distribution space). Bioavailability for subcutaneous administration is typically 50-80%. Pharmacodynamics (what drug does to body) describes drug effect over time: Emax (maximum effect), EC50 (concentration for 50% effect), receptor occupancy, and duration of response. PK/PD modeling relates exposure to response, guiding dose selection. Biologics differ from small molecules: larger, target-mediated drug disposition (TMDD), immunogenicity affecting PK, longer half-lives, and less tissue penetration. Understanding PK/PD enables optimal dosing regimens.