Difference between a generic biological product and a biosimilar

A biosimilar refers to a biological product which is highly similar to a pre-existing and approved biological product (reference product), and does not clinically differ in terms of safety and effectiveness from the reference product. A biosimilar may also additionally meet standards for interchangeability with reference product.  A biosimilar needs to have the same mechanism of action as its reference product i.e. it must work in the same way as the reference product. For regulatory purposes a biosimilar should posses same mechanism of action, route of administration, dosage form, and strength as the reference product. Additionally, a biosimilar may also be prescribed for the indications and conditions of use that have been previously approved for the reference product.

Generic (chemical) drugs have the same active ingredient, safety and efficacy and they are used in the same dosage form, strength, and route of administration as the innovator drug. Therefore technically brand-name and generic drugs are considered same as the innovator product. Biosimilars, on the other hand, are considered to be highly similar (not same) to the reference (innovator) product but has allowable differences in the composition etc. The biosimilars, however, do not have clinically significant differences in terms of safety, and potency from the reference product.

This is because unlike chemical generics, biosimilars are structurally more complex and 200 to 1,000 times the size of a generic drug. Further, in terms of manufacturing, biosimilars are manufactured in living cells, then extracted and purified, whereas generics are manufactured purely through chemical synthesis.  Just like generics, biosimilars provide a huge cost advantage over the reference drug while serving the same purpose. They often cost a fraction of the innovator product.