The aim of this discussion was to explore the concept and purpose of repositioning drugs, understand the boundaries that still underlie the technique and, analyze repurposed drugs, so they can serve of inspiration for the future of drug discovery and development. Drug repurposing, often also mentioned as drug repositioning is defined as the rational use of know drugs for new indications in order to increase pharmaceutical industry productivity and deliver therapeutic options to patients who suffer from chronic, orphan, neglected, rare, untreatable diseases or pathologies with poor therapeutic approaches. The limitations of this method are the same as in de novo drug development, the idiosyncrasy of both the disease and patient, the acquired resistance to therapy, the bureaucracy implicated in the submission of a drug's approval request and the lack of scientific knowledge to target certain pathologies, makes it hard and risky to develop and commercialize whether a new molecule or an old drug for a new indication. The methods of drug repositioning may be classified in treatment oriented, disease or drug oriented. The methodologies may not require an elevated level of scientific knowledge as serendipity testing or may, on the other hand, demand the comprehension of the shape and binding properties of the substance, as molecular docking. Drug repositioning presented the community with useful therapeutic approaches and, at the same time, has increased the profit of drugs which had been already abandoned. Examples such as thalidomide, a drug created for motion-sickness that was found to be teratogenic, it was later on repurposed for multiple myeloma. Sildenafil, a drug that started out as a low efficacy anti-anginous, but proved to be useful in erectile dysfunction and in pulmonary hypertension. Duloxetine, an old anti- depressant repurposed to syndrome of urinary incontinence, neuropathic pain and to generally anxiety disorder in children, due to one same mechanism of action. Drug repurposing is a fructuous approach for the development of new therapeutics, nevertheless several points have to be enlightened and simplified. Protocols of methods have to be created in order to achieve maximization of time and costs. The legal framework should be simplified, by reducing the heterogeneity between international agencies.

Trabalho Final de Mestrado Integrado, Ciências Farmacêuticas, Universidade de Lisboa, Faculdade de Farmácia, 2015