The bioavailability of a drug measures the amount of the drug that is absorbed and made available to perform its therapeutic activity in the body. A drug administered intravenously will have a bioavailability of 100%, as it enters directly into circulation and is immediately available to organs and tissues. In contrast, drugs administered by other routes (e.g., orally) will have lower bioavailability due to partial absorption.

The patent ensures the holder exclusive ownership of all industrial property rights – and consequently the use and exploitation – of the patented product for the duration of the patent. This constitutes a sort of temporary monopoly right in favor of the holder. The allocation of these exclusive rights is intended to remunerate the costs incurred and investments made by the patent holder in the design and development of the patented product, thereby serving as an incentive for research.

The regulation of pharmaceutical product patents in Italy dates back to 1979, the year of issuance of Presidential Decree 338. In the case of drugs, the need to demonstrate efficacy and safety through long clinical trials means that years elapse between obtaining the patent and receiving the Marketing Authorization for the patented medicine. For this reason, the legislation provides for additional protection of up to 5 years, allowing the patent holder to recover, at least in part, this delay in the economic exploitation of the invention. This additional protection is called the SPC (Supplementary Protection Certificate).

When one or more generic medicines of a drug reimbursed by the NHS, whose patent protection has expired, are authorized, the Italian Medicines Agency (AIFA) includes both the originator and the corresponding generics in a list, called the transparency list, which is updated monthly and available on the AIFA website.

In this list, the originator medicine and the corresponding generics are listed together, with the corresponding reference price. The drugs grouped together in the transparency list are substitutable. This list thus confirms that the medicines listed are considered generics and establishes their substitutability.

An originator medicine, or reference medicine, is a medicine authorized based on a complete dossier, including data on chemical quality, pharmaco-toxicology (tests on laboratory animals), and clinical (controlled studies on patients). A medicine authorized on this basis is sold under a monopoly by the company that developed it for the duration of the patent protection. Conversely, a generic medicine is a medicine that has the same active ingredient, the same dosage, and the same pharmaceutical form as the originator but is authorized after the originator's patent protection has expired, upon demonstration of chemical quality and bioequivalence to the originator. Since this medicine is bioequivalent, it can refer to the pharmaco-toxicological and clinical data collected by the originator.

The term active ingredient refers to the substance in a drug that has therapeutic activity. The remaining components of a pharmaceutical form are called excipients and are used to improve its stability, preservation, administration, or even to modify the release rate of the active ingredient.