Research design strategies to evaluate the impact of formulations on abuse liability

Scheduling of a chemical drug substance under the Controlled Substances Act (CSA) includes an evaluation of preclinical and clinical safety, and experimental abuse liability studies, as well as information on diversion and overdose. Formulations that mitigate abuse liability, dependence potential and public health risks (e.g., altered absorption rate and tamperability, long half-life, pro-drugs and combination products) are amenable to preclinical and clinical studies to compare their abuse potential to reference compounds. For new formulations (NF) as marketed agents, direct comparison to the immediate release (IR) formulation of the reference compound is typically needed across the full range of potential studies. While the public health advantage of formulation changes in the marketplace can be conceptualized in behavioral economic terms, generating persuasive data is challenging. Study complexity increases because of additional conditions (e.g., placebo, 2-3 doses of the IR formulation, 2-3 doses of the new formulation, and 2-3 doses of the unscheduled or negative control drug), larger sample sizes (study power driven by the comparison of the new formulation versus the IR or placebo), and associated increases in study duration. However, the use of single maximal doses of well-characterized controls can reduce the number of study arms, and using incomplete block designs can reduce study duration. Less typical experimental approaches may also be useful, such as human choice or discrimination procedures, or pre-marketing consumer studies among experienced drug tamperers. New formulations that demonstrate a substantial difference from marketed or reference products have a potential marketing advantage and should require less onerous risk management. Post-marketing epidemiological data demonstrating the lack of abuse will carry the most weight from a public health and physician perspective.