dosedependence

Dosedependence is the term used to describe how the magnitude or probability of an effect varies with the dose of a substance. In pharmacology and toxicology, this relationship is typically depicted as a dose–response curve, which characterizes how probability or magnitude of an effect changes with dose. At low doses there may be little or no effect, followed by a threshold beyond which effects rise toward a maximum in a sigmoidal fashion. The curve is often summarized by parameters such as the effective dose for a given response (ED50), the maximal effect (Emax), and the potency reflected in the dose at which half-maximal response is achieved (EC50).

While many drugs exhibit monotonic dose dependence, some substances show non-monotonic or biphasic responses, where low and high doses produce different or opposing effects. Hormesis is a related phenomenon where small doses stimulate a response that is reversed at higher doses. Factors such as pharmacokinetics, receptor occupancy, and downstream signaling shape the curve.

Various factors influence dose dependence: individual genetics, age, sex, health status, interactions with other medications or foods, and repeated exposure leading to tolerance or sensitization. Pharmacokinetics (absorption, distribution, metabolism, excretion) determine the internal dose, while pharmacodynamics determine the response at target sites.

Practical implications include establishing therapeutic windows and safety margins. The therapeutic index or margin compares a dose that produces toxicity with a dose that achieves therapeutic benefit. Understanding dose dependence helps optimize dosing regimens to maximize efficacy while minimizing adverse effects and risk of overdose.