Principles of pharmacology and pharmacokinetics - dose-response relationship

Definition

The dose-response relationship describes how drug effect changes with dose - typically following a sigmoidal curve with a threshold (minimum dose for detectable effect), a linear-appearing middle portion, and a plateau (maximum effect, beyond which further dose increases add toxicity without added benefit) - understanding this shape informs rational dose titration
A foundational pharmacological concept underlying dose selection and titration decisions across all of clinical pharmacology

Efficacy (the maximum effect a drug can produce, reflected in the curve's plateau) and potency (the dose required to produce a given effect, reflected in the curve's position along the dose axis) are distinct concepts - a more potent drug is not necessarily more effective, since two drugs can have identical maximum efficacy while requiring very different doses to achieve it

Individual variation in dose-response (genetic, age, organ function, drug interaction factors) means population-level dosing guidance requires individualised titration in practice, particularly for drugs with a narrow therapeutic index where the margin between effective and toxic dose is small

Titration to effect (rather than a fixed dose applied uniformly) is standard practice for many drug classes, starting low and increasing gradually while monitoring for both efficacy and emerging toxicity
Understanding where an individual patient sits on the dose-response curve helps predict whether further dose increase is likely to add meaningful benefit (still on the rising portion) or mainly add toxicity risk (already near the plateau)

Ceiling effect drugs (e.g. partial opioid agonists like buprenorphine, where effect plateaus at a dose beyond which further increase adds little additional analgesia but continues to add risk with full agonists), potency vs efficacy distinction (a frequently confused pair of terms), narrow therapeutic index dose titration

Potency and efficacy are frequently confused but are distinct concepts - a highly potent drug (effective at a low dose) is not necessarily more effective (able to produce a larger maximum effect) than a less potent alternative, and dose selection should be guided by the desired clinical effect, not by assuming a more potent drug is inherently superior

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.