What are factors affecting half-life of a drug?

Decrease of drug clearance or increase in volume of distribution increases it Effect on Vd: aging (decreases muscle mass so decreases it) Obesity (increases fat tissue so it increases) Effects on clearance: CYP induction (decrease) or inhibition (increase) Cardiac failure (decrease clearance), hepatic failure or kidney failure (decrease clearance) so increase half-life So doses of drugs are given according to drug responsiveness on half-life