Chapter 32 — Chapter 32 — Medicine, Agriculture and Industry

Pharmacology deals with what a drug does and its safety margins; every drug may be a potential poison — the difference lies in the dose. Therapeutic window: the range of plasma drug concentrations that are effective without harmful side effects (the 'sweet spot'). Minimum effective concentration (MEC): lowest level below which there is no clinical effect. Minimum toxic concentration (MTC): lowest level at which adverse effects begin. Duration of action: time the concentration stays within the window. A wide window is safer and flexible; a narrow window needs careful dosing and blood checks. Multiple medicines, genetics, obesity, age and health affect the window. Therapeutic index (TI) is a quantitative measure of safety comparing the toxic dose with the effective dose: TI = TD50/ED50, where TD50 causes toxicity in 50% of people and ED50 works in 50%. Higher TI = safer (TI 10 safer than TI 2). Penicillin and paracetamol have high TI; warfarin and digoxin have low TI and need therapeutic drug monitoring (TDM).