I never said it was easy, only that there are strong incentives to do so. I even went out of my way to say it is tricky. Here's something for you if you are interested to dig in deeper:
This article discusses certain issues to be considered when trying to obtain new patent protection for repurposed drugs. It should be expected that each attempt to patent a repurposed drug will have its own factspecific challenges. Accordingly, the concepts discussed here are generalized and nonexhaustive.
More recently, failed drugs previously considered to be lost causes are being reconsidered as possible therapies for different indications than those for which they had originally been considered. Such drug "repurposing" provides researchers and clinicians with a cost-effective way to identify potential new therapies without needing to start from scratch. Many failed drugs have already established their relative safety in Phase I clinical trials, which can simplify and reduce the cost of obtaining FDA approval should a new indication be found. Drug repurposing is not limited to failed drugs but is also being considered for currently marketed drugs as well as "off patent" generic compounds to expand and extend their usefulness.
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A further approach to obtaining claims directed to previously known drugs that are patentable in a § 102 context is to draft claims to novel pharmaceutical dosage forms. Pharmaceutical dosage forms can be, for example, solids, liquids, delayed or extended release forms, and/or for a specific type of administration (e.g., oral, parenteral, intramuscular, etc.). Many types of variations are possible with pharmaceutical dosage forms, which lend themselves to drafting novel claims. For example, desired release characteristics and/or routes of administration may differ for the new use of the repurposed drug compared to its previous use, which would provide the basis of a novel claim.
As a final and particularly important example, a method claim reciting a repurposed drug may more easily overcome § 102 rejections. Repurposing a drug for a new indication is typically a novel use of the drug. Therefore, a method-of-use claim that recites a repurposed drug for treating a subject with the new indication should also be novel. Such method claims are particularly useful because they are difficult for competitors to design around, and they are also available in many foreign jurisdictions (though with potentially different formats).
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