Interdose

Interdose is a term used in pharmacology and medicine to denote the interval between successive doses of a drug in a dosing regimen. It is most often described in schedules such as every 8 hours or once daily.

Purpose: The interdose interval is chosen to maintain drug concentrations within the therapeutic window, achieving efficacy while minimizing toxicity. It interacts with dose size and the drug’s pharmacokinetic profile to produce a stable steady state.

Determinants: The interval is influenced by the drug’s half-life, clearance, and distribution, as well as formulation (immediate- or extended-release), route of administration, and patient factors such as age, kidney or liver function, and drug interactions.

Clinical implications: Shorter intervals are used for drugs with short half-lives; longer intervals or depot formulations are used for drugs with long half-lives. The aim is to keep trough levels above the minimum effective concentration but below toxic levels.

Examples: Antibiotics are commonly dosed with fixed intervals (for example, amoxicillin 500 mg every 8 hours). Other drugs may be given once daily or every other day depending on half-life and clinical goals.

See also: dosing regimen, pharmacokinetics, half-life, steady state.