Global Core Electronic Medicinal Product Information (ePI), published by HL7 International / Biomedical Research and Regulation. This guide is not an authorized publication; it is the continuous build for version 1.1.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/HL7/emedicinal-product-info/ and changes regularly. See the Directory of published versions

Dosing and Population Model

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This page describes how the ePI represents populations and structured dosing, and the rules that keep the two consistent. It is the normative companion to the Group (ePI) and MedicationKnowledge (ePI) profiles.

The shape of the problem

Product information stratifies both clinical use (which indications, contraindications, interactions, warnings and undesirable effects apply to whom) and dosing (how much, how often, for how long) by population. A single drug routinely carries many indications, each with several populations, each with one or more dosing regimens. The model below keeps a single source of truth for population while still allowing dose to vary within an indication.

Group is the canonical population

A population is always a Group (ePI) resource. It is definitional (defined by criteria, not an enumerated member list) and describes one or more axes as characteristic entries, combined with AND:

Axis	characteristic.code	value
Sex	sex	CodeableConcept (administrative gender)
Age	age	Range (UCUM a years / d days)
Body weight	body-weight	Range
Race	race	CodeableConcept
Lifestyle	lifestyle	CodeableConcept
Renal function	renal-function	Range (e.g. creatinine clearance in mL/min)
Hepatic function	hepatic-function	CodeableConcept
Immune status	immune-status	CodeableConcept

The characteristic slicing is open: real labels stratify on axes not listed here, and authors may add further characteristic entries. Each ClinicalUseDefinition.population references one of these Groups.

Dosing links to indication; population stratifies the dose

Structured dosing lives in MedicationKnowledge under indicationGuideline:

• indicationGuideline.indication references the Indication ClinicalUseDefinition — the dose is keyed to the indication.
• indicationGuideline.dosingGuideline.dosage carries the structured regimen: dosage.type (loading/maintenance/…), timing, doseAndRate (absolute amounts, ranges, or weight-based mg/kg rates), boundsDuration, maxDosePerPeriod.
• indicationGuideline.dosingGuideline.patientCharacteristic stratifies the dose within a single indication, using the same axis vocabulary as Group.characteristic (the Group Characteristic Type value set).

Rule 1 — Do not double-encode the population

There are two places a population can appear: on the indication's ClinicalUseDefinition.population (a Group) and on the dose's patientCharacteristic. Use exactly one:

• When the dose population equals the indication population, populate ClinicalUseDefinition.population and leave patientCharacteristic empty.
• Use patientCharacteristic only to split a dose into sub-populations within one indication (e.g. adult vs child vs term-newborn dosing for the same condition).

The Diflucan example shows both: mucosal candidiasis (general indication, three dose rows keyed by age) and invasive candidiasis (adults, population on the CUD, dose row with no patientCharacteristic).

Rule 2 — Organ-function adjustments are a single guidance block, not a table

Renal- and hepatic-impairment dosing is usually expressed as a modifier of every other indication's dose (e.g. "give 50% of the recommended dose when CrCl ≤ 50 mL/min"). FHIR Dosage cannot express "a percentage of the indication dose", and enumerating an adjusted dose for every indication × impairment band explodes the bundle and misrepresents a rule as a table.

Therefore:

• Represent the affected population once as a Group (e.g. a renal-function Range).
• Represent the adjustment once as guidance — a Warning ClinicalUseDefinition whose population references that Group and whose text states the rule — and/or as narrative in the posology section.
• Do not replicate impairment-adjusted doses across indications.

Rule 3 — dosage.text is authoritative; structure is best-effort

Some dosing is irreducibly narrative ("use adult or paediatric dosing per weight and pubertal development", "longer if immunocompromised"). Always provide a human-readable dosage.text; populate the structured fields as far as they faithfully capture the regimen. dosage.type may be coded where a suitable code system exists, otherwise use text (loading/maintenance/initial rarely have standard codes).

Two roles of weight

Weight appears in two distinct places — keep them separate:

• Population selector — Group.characteristic[body-weight] (e.g. patients ≥ 40 kg).
• Dose denominator — a mg/kg rate in Dosage.doseAndRate (e.g. 6 mg/kg).

Severity

Disease severity ("up to 800 mg in severe disease") is a property of the condition, not of the patient, so it is not a population axis. Carry the mild-to-severe span in the dose range plus dosage.text.