A search for interaction among combinations of drugs of abuse and the use of isobolographic analysis

Abstract

Individuals who abuse drugs usually use more than one substance. Toxic consequences of single and multi-drug use are well documented in the Treatment Episodes Data Set that lists drug combinations that result in hospital admissions. Using this list as a guide, we focused our attention on combinations that result in the most hospital admissions and searched the PubMed database with the objective of determining the number of such publications and, in particular, those that used the term synergism in their titles or abstracts. Using the search criteria produced an extensive list of published articles. However, a further intersection of the search terms with the term isobole revealed a surprisingly small number of literature reports. Because the method of isoboles is the most common quantitative method for distinguishing between drug synergism and simple additivity, the small number of investigations that actually employed this quantification suggests that the term synergism is not properly documented in describing the toxicity among abused substances. The possible reasons for this lack of quantification may be related to a misunderstanding of the modelling equations. To help rectify this possible hurdle to understanding and clinical utility, the theory and modelling are discussed here.