Underdosing

Underdosing refers to taking less medication than prescribed or required for a given condition. It yields subtherapeutic drug concentrations in blood and tissues, which can lead to inadequate clinical response. Underdosing can be intentional, to limit adverse effects, or unintentional, arising from poor adherence, misunderstanding of dosing instructions, or prescription and dispensing errors.

Causes include nonadherence; incorrect dosing based on mistakes in weight, age, or indication; pharmacokinetic variability such as rapid metabolism or reduced absorption; drug interactions that lower bioavailability; and formulation issues, such as long-acting products used at an insufficient dose. Economic or access barriers can also contribute.

Consequences include treatment failure, relapse or progression of illness, and an increased risk of resistance, especially with antimicrobial agents. Subtherapeutic exposure can select resistant organisms and diminish future treatment options. Persistent symptoms may lead to additional healthcare encounters.

Management focuses on ensuring appropriate exposure: confirm the prescribed dose with the patient, assess and support adherence, and adjust the regimen as needed. Therapeutic drug monitoring may help for drugs with narrow therapeutic indices. Review interactions and absorption issues, and verify suitable formulation and administration timing. Public health strategies emphasize clear guidelines and access to properly dosed medications to prevent underdosing.