To better define the use of IL-6 therapies, we developed an algorithm to mathematically model inhibition of IL-6 activity in the presence of siltuximab (an anti-IL-6 therapy), tocilizumab (an anti-IL-6R therapy) or both in two scenarios: first, representative of iMCD, with persistently high IL-6 production; and second, representative of severe COVID-19, with a cytokine storm and massive IL-6 production. The gene discussed is IL6R; the disease is COVID-19.