Drug Substance vs. Drug Product
The difference between ‘drug substance’ and ‘drug product’ is important to understand and can really help with the successful development of your pharmaceutical drug.
What’s the difference between the two terms?
The drug substance, depending on its purity, is mostly composed of the API (active pharmaceutical ingredient) or the ‘naked’ drug without excipients. The API is what will have a therapeutic effect inside the body as opposed to the excipients which serve to package and deliver the API.
The drug product is the formulated mixture of the drug substance and excipients either as a prototype or as the final marketed dosage form.
Biorelevant solubility and dissolution tests
The drug substance is obtained after drug candidate selection, very early in development and before drug product development. To develop a drug product (the final formulated drug) from a drug substance it’s important to understand the drug substance’s physicochemical properties. Biorelevant solubility testing of the drug substance is performed to understand the compound’s solubility and therefore choose the right formulation strategy.
Once the drug substance is developed and formulated into a drug product, i.e. the prototype or final oral dosage form, the drug product can be tested in suitable media (ideally biorelevant/physiologically relevant media) for dissolution testing prior to clinical studies. Biorelevant dissolution testing gives an insight into how a drug product would dissolve in vivo.
The take-home message
Understanding the difference between drug substance and drug product is essential for choosing which in vitro tests to perform.