The Generic Product Identifier (GPI) is a 14-character hierarchical classification system that identifies drugs from their primary therapeutic use down to the unique interchangeable product regardless of manufacturer or package size. The code consists of seven subsets, each providing increasingly more specific information about a drug available with a prescription in the United States.
The first six characters of the GPI define the therapeutic class code, the next two pairs the drug name, and the last four define route, dosage or strength. For example GPI 58-20-00-60-10-01-05 is for the drug Nortriptyline HCL cap 10 mg (an antidepressant) and can be further classified as follows:
58 Drug group Antidepressants 58-20 Drug class Tricyclic agents 58-20-00 Drug sub-class 58-20-00-60 Drug name Nortriptyline 58-20-00-60-10 Drug name extension Hydrochloride 58-20-00-60-10-01 Dosage form Capsule 58-20-00-60-10-01-05 Strength 10 mg
Alternate drug classification systems include the AHFS Drug Information brand run by the American Society of Health-System Pharmacists and First DataBank's Generic Sequence Number (GSN).
Wolters Kluwer provides a database under the Medi-Span brand called Medispan Electronic Drug File that links this code to other prescription drug classification codes commonly used for payment and analysis in the United States Health Care System, as well as embedded drug information like adverse drug effects.