Foster-Carman index

On the basis that dose-effect relationships are geometric and not arithmetic, Foster (42) felt that simple ratios of the reacting times would not give a straight line when plotted against dosage but that sufficient data were 

Foster and Carman calculated their analgesic index (actually a reflex depression index) from the relation, where U is the normal re- 

10 sec. gives an index of 1.58 if the normal reaction time is just 4.0 sec. When the Foster-Carman index is plotted against dose, approximately straight-line curves are obtained. 

The effect of the dosage of morphine on the analgesic index (reflex depression index). The subcutaneous dosage of morphine for rats is plotted on the ab-scissa and the reflex depression index on the ordinate. The index is given by Vl/fo where to is reaction time prior to morphine and t is the altered reaction time. (Copied from J. Lee (4).) 

The relationship between doses of morphine and demerol required to induce equivalent reflex depression in rats. The dose of morphine is plotted on the abscissa and the equivalent dose of demerol on the ordinate. Calculated from Figs. 1 and 2. C(d)/2)(m) - 12.64 - 4.89/D(m). 

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Metliod AD 90% Beecher Thermal radiation of forehead Von Frey hairs on face Clinical doses Thermal radiation Foster-Carman index 1.40 Thermal radiation AD 50/100 Von Frey hairs on cornea after procaine Thermal radiation AD 50/100... 

Two curves using the Foster-Carman index are shown in Fig. 1 and Fig. 2. From Figs. 1 and 2, according to Lee, at an index of 1.25 morphine is 20 times as active as demerol, whereas at an index of 1.40 it is 12 times as active this indicates the desirability of comparing a series of compounds at the same analgesic (reflex depression) level (4). 

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