The most common approach for the new use of an "old" drug is off-label prescribing by doctors, often considered "innovative clinical care". Doctors get their motivation to prescribe off-label from sources like evidence in medical literature, presentations at professional conferences, and medical professional word-of-mouth. One challenge of off-label use is that insurance companies may not reimburse, leaving the patient to carry the financial burden of this innovative clinical care. However, insurance companies periodically review the value of off-label use through guided review of the medical literature and through a detailed risk-benefit analysis. If the story is good – that the new use for an old drug reduces health care costs – then off-label use can be included in the insurer's drug formulary, and the prescription gets covered.
The more formal route for repurposing is to actually seek FDA approval. The original drug company could revise their own drug label to include this new use. This is achieved through a Supplemental New Drug Application, and requires new clinical trial data supporting the safety and efficacy of the drug for its new use. This approach can be expensive; the SNDA could cost just over $1 million to submit to FDA, and the application may not even be approved! Also, this cost does not include the expense of conducting the evidence-providing clinical trials.
A more common FDA pathway for repurposing is the 505(b)(2) New Drug Application. A 505(b)(2) application contains full safety and effectiveness reports, but allows at least some of the information required for approval to come from studies not conducted by or for the applicant. Because approval can rest in part on data already accepted by the FDA, or otherwise available in the public domain, fewer and smaller studies may be required – reducing costs and development time. This is a win-win for patients and industry, alike. Today, the 505(b)(2) speeds FDA approval for a wide range of products, especially for those that represent a limited change from an existing or approved drug. Ideal candidates include: new indications for an approved drug; changes in the original drug dosage form, strength, formulation, dosing regimen or route of administration; and new combination products (like the combination of two approved drugs). In 2013, over 50% of all new FDA drug approvals were by the 505(b)(2) pathway...and that percentage grows each year. FDA approval through the 505(b)(2) path is a financial incentive for companies to pursue repurposing. And as for the challenge of insurance coverage for patients, the reimbursement effort is easier and faster with FDA approval.
While "innovative clinical care" is the fastest route to repurposing, it may not achieve the breadth of patient use that formal FDA approval would achieve. Still, both approaches are complimentary for enabling cures within reach and impacting unmet medical needs.