Isobolographic

Isobolographic is an adjective used to describe methods that involve isobolograms, graphical representations used to study interactions between two or more drugs or chemicals. In pharmacology, isobolographic analysis (also called isobolography) is a graphical method for determining whether drug combinations are additive, synergistic, or antagonistic.

The method relies on dose–response data for each drug. For a defined effect level (such as the ED50, the dose producing 50% of the maximal effect), the individual doses of each drug that achieve that effect when given alone are identified. On a two-dimensional plot, the dose of drug A is placed on the x-axis and the dose of drug B on the y-axis. The line connecting the two single-drug ED50 points on the axes is the line of additivity (the isobole) under Loewe additivity assumptions. Observed combinations of A and B are then plotted as points relative to this line: points on the line indicate additivity, points below indicate synergy (less drug is needed than expected), and points above indicate antagonism (more drug is needed than expected). In practice, the shape of the isobole can vary with potency differences and nonlinearity of the dose–response curves.

Isobolographic analysis is widely used to assess drug interactions in pharmacology, toxicology, and medicinal chemistry and can be applied to different effect levels (ED50, ED75, etc.). It may be complemented by quantitative indices such as the fractional inhibitory concentration (FIC) index. Limitations include reliance on accurate dose–response data and assumptions of dose–response consistency and Loewe additivity.