tooluniverse-drug-synergy

Bliss synergy is calculated as the observed combination effect minus the expected effect E_a + E_b − E_a·E_b, using fractional inhibition values between 0 and 1. Run the DrugSynergy_calculate_bliss tool with effect_a, effect_b, and effect_combination to get the score and interpretation.

The model depends on your data: Bliss for a single dose pair, HSA for multiple dose points, Loewe or Combination Index when you have single-agent dose-response curves, and ZIP for a full dose-by-dose viability matrix. Each model defines additivity differently, so state which one you used.

Bliss assumes drugs act independently, Loewe assumes a drug combined with itself is additive (dose equivalence), and ZIP combines both by measuring potency shifts in dose-response curves. They can legitimately disagree for the same combination, so reporting two models is good practice.

Only ZIP accepts percent viability directly; Bliss, HSA, and Loewe require fractional inhibition on a 0-1 scale. Convert viability first with inhibition = 1 − viability/100, since mixing scales is the most common analysis error.

Common causes are scale mismatches, ceiling effects when both single agents already inhibit near 100%, and insufficient dose points for Loewe, CI, or ZIP, which need at least three non-zero measurable doses per drug for the Hill fit. A synergy score is also not a statistical test, so replicate measurements for confidence.