La substitution refers to the practice in pharmacy of dispensing a medication other than that prescribed by the doctor, without the knowledge of the prescriber. The criterion that usually prevails in this decision is an economic criterion.
It is important to distinguish the concepts of “substitution” and “exchange”. In the case of Spain, the substitution of a biological medicine for another is not allowed, so that if a doctor prescribes an original biological, the pharmacist cannot dispense another, be it original or biosimilar. Likewise, if the prescribed medication is a biosimilar, the pharmacist cannot dispense either another biosimilar or its reference original.
This policy of “no substitution” of treatment is basically preventive, since there is no evidence that administering a new biological drug to a patient undergoing treatment causes any adverse effect.
In hospitals, where Pharmacy and Therapeutics Commissions are the decision-making body, it is essential that a consensus be reached with physicians regarding the selection of biological drugs.
On the other hand, it is called exchange the practice whereby the prescribing physician changes the biological treatment for another analogue for clinical or other reasons. This situation frequently occurs among originator biologics without particular harmful effects having been reported.
Thus, it is estimated that the reciprocal exchange between two products that have passed a comparability exercise as comprehensive as the biosimilar and its corresponding originator reference product, it should not be associated with significant clinical risk. In any case, it is the prescribing physician who, in light of the evidence, must establish the convenience, or not, of exchanging both products.