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  • Define active pharmaceutical ingredient1 (API) and drug product (finished dosage form).

  • Define pharmaceutical equivalence (PE) and therapeutic equivalence (TE).

  • Describe the physical and biopharmaceutical properties of API important in the design and performance of drug products.

  • Discuss why physical and biopharmaceutical properties of the API and the drug product are interrelated and important in drug product design and performance.

  • Describe the main methods used to test (PE) of the active ingredient (API) or the dosage form (drug product).

  • Explain the relationship of PE, bioequivalence (BE), and therapeutic equivalence (TE).

  • Explain whether a generic drug product that is not an exact PE can be TE.

  • Explain why a generic drug product with identical PE may not lead to equivalent pharmacokinetic and pharmacodynamic performance.

1The active pharmaceutical ingredient (API) is also referred to as the drug substance. Both drug substance and API will be used interchangeably in this chapter.


In order to bring a new drug to the market, a company must submit a new drug application (NDA) to the FDA for review and approval. Regulatory approval is based on evidence that establishes the safety and efficacy of the new drug product through one or more clinical trials (FDA, cited June 5, 2014). The development of a new drug, from discovery to entering the market, is a lengthy and expensive process. These clinical studies are typically performed by a large pharmaceutical company known as the innovator company. The innovator company patents the new drug and gives it a brand name. The brand drug product is available from only one manufacturer until patent expiration. These drug products are also known as single-source drugs, which are marketed at a high price, a practice that allows the company to recover the costs in development and to make a profit. The patents are critical for encouraging innovation that is needed for developing new drugs to effectively treat diseases. Once the patent expires, other companies can make and market the generic versions of the brand drug product after gaining approval for marketing by a regulatory agency through an Abbreviated New Drug Application (ANDA) process, which presents a substantially lower barrier than the NDA process (Fig. 17-1). At that point, the drug becomes a multisource drug, provided the generic drug products contain the same active pharmaceutical ingredient (API) in the same dosage form and given by the same route of administration (Chapter 16). Through market competition, the price of a multisource drug is significantly lower than the single-source brand drug. It was estimated that the substitution of for brand-name drugs by generics saved buyers $8–10 billion dollars in the US in 1994 (Cook et al, 1998). This number is undoubtedly much higher today. This makes the drug more readily affordable to the general public. The competition of generic drug products reduces global healthcare costs and motivates brand name ...

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