A pharmacopoeia is an official book of standards for medicines: for each medicine, it says what the medicine must contain, how pure it must be, and which tests a laboratory must run to prove it. The standard for one medicine is called a monograph. A drug maker must show that a batch meets the monograph before it may release the batch for sale. The word is also spelt pharmacopeia, mostly in America.
India's own book is the Indian Pharmacopoeia (IP). It is published by the Indian Pharmacopoeia Commission, a government body in Ghaziabad, and medicines sold in India must meet it under the Drugs and Cosmetics Act. Medicines sold in America must meet the United States Pharmacopeia (USP), which is published by a nonprofit organisation. This matters to India, because India makes a large share of the generic medicines sold in America. A generic medicine is a cheaper version of a medicine whose patent has expired.
Today a pharmacopoeia is mostly an online database, not a printed book. It is sold by subscription to drug makers, testing laboratories and regulators. The publisher revises it several times a year, as new impurities are found or better tests are developed. Selling the standard is a form of data as a service: the publisher earns from the data itself.
Take, for example, the monograph for metformin tablets, a common medicine for diabetes. It says that each tablet must contain between 95% and 105% of the amount printed on the label. It sets a dissolution test, which checks how quickly the tablet dissolves in a liquid that imitates the stomach. It lists the impurities that may be present, and the highest amount allowed for each. And it gives the exact method for each test, such as the chromatography method that measures the medicine and its impurities.
At a drug maker, the quality control laboratory loads each monograph's tests into its laboratory information management system (LIMS), the software that logs each sample and its results. When the pharmacopoeia revises a monograph, the quality management system (QMS) for pharma records a change control, a formal record of the change and of who approved it. The laboratory updates its method before the new standard takes effect. Every result must be recorded and signed so that an inspector can check it later, under GxP rules.
Alongside the written standard, the publisher also sells pharmaceutical reference standards. These are carefully made samples against which laboratories compare their own test results.
How is a pharmacopoeia different from a drug approval? A drug approval, given by a regulator such as CDSCO in India or the FDA in America, allows one company to sell one product. A pharmacopoeia sets the quality standard that every maker of that medicine must meet.