Unlike the therapeutic ratio, this measure is independent of the shapes of the cumulative quantal doseвЂ“effect curves for the therapeutic and toxic effects. If the CSF <В 1, there is overlap between the maximally effective ( ED 99) and minimally toxic ( TD 1) doses. A CSF >В 1 indicates that the dose effective in 99% of the population is less than the dose that would be toxic in 1% of the population. The certainty safety factor (CSF) is the ratio of. Therefore, an index that uses the lowest toxic and highest therapeutic doses is more consistent with this goal than the therapeutic ratio. The goal of drug therapy is to achieve the desired therapeutic effect in all patients without producing toxic effects in any patients. However, this ratio of toxic to therapeutic dose may not be consistent across the entire dose range if the doseвЂ“effect curves for the therapeutic and toxic effects are not parallel. A therapeutic ratio of 2.5 means that approximately 2.5 times as much drug is required to cause toxicity in half of the patients than is needed to produce a therapeutic effect in the same proportion of patients. The therapeutic ratio is a ratio of the dose at which 50% of subjects experience the toxic effect to the dose at which 50% of patients experience the therapeutic effect. The TD 1 and TD 50 are the doses that cause the toxic effect in 1% and 50% of the population, respectively. The ED 50 and ED 99 are the doses required to produce the drugвЂ™s therapeutic effect in 50% and 99% of the population, respectively. Cumulative quantal doseвЂ“effect curves for a drugвЂ™s therapeutic and toxic effects.

Therapeutic index range