IUkg

International Units per kilogram (IU/kg) is a dosing metric used in pharmacology and medicine to express the amount of a biologically active substance required per unit of body weight. An International Unit (IU) is a substance-specific amount defined by its biological effect rather than a fixed mass; as a result, IU/kg is not a universal mass-based measure and requires reference to the standard for each substance. Dosing with IU/kg is common when potency varies between preparations or when patient size influences response, such as vitamins, hormones, or some biologic medicines. The total dose is obtained by multiplying the weight in kilograms by the IU/kg value prescribed.

Because IU is defined per substance, conversions to mass units (grams, micrograms) depend on the substance. For example, cholecalciferol (vitamin D3) has 1 microgram equal to 40 IU; other substances have different relationships.

In practice, IU/kg dosing supports individualized treatment in pediatrics and adults, aligning potency with body weight to balance efficacy and safety. Regulatory labeling often specifies IU/kg or IU per dose, with the per-subject dose adjusted by weight, age, and clinical context.