THE ABSORPTION OF 4:4'-DIAMIDINO STILBENE (STILBAMIDINE) BY TRYPANOSOMES AND ITS BLOOD CONCENTRATION IN ANIMALS

¹ From the National Institute for Medical Research, London, N. W. 3

rate of trypanocidal action of stilbamidine in vitro for T. equiperdum, the conditions described in the paper, is in approximate agreement with equation:

[See equation in the PDF file]

Stilbamidine is absorbed by trypanosomes in vitro with moderate rapidity. When equilibrium is reached, there is a quantitative relation between the concentration inside the trypanosome and that outside (over the range of concentrations studied, the concentration inside is about 1,400 times as great as the concentration outside). Absorption during its early stages is reversible. Absorption of stilbamidine by trypanosomes also occurs in vivo.

It is calculated that the amount of stilbamidine required under these experimental conditions to kill a trypanosome in 4 hours at 37°C, is 7.3 x 10^–8 molecules.

The behaviour of stilbamidine towards trypanosomes is closely similar to that of trivalent arsenicals and of acriflavine, although the facts about drug-resistance (2) indicate that stilbamidine is absorbed by a different part of the parasite from that which absorbs these other compounds.

Curves are given showing the concentration of stilbamidine in the plasma of rabbits and mice following intravenous or intraperitoneal administration. The compound rapidly disappears from the plasma. Sufficient stilbamidine was injected intravenously into rabbits to yield a (theoretical) concentration of 16 mgm. per 100 cc.; after two hours the actual concentration was about 0.05 mgm. per 100 cc. and after six hours it was less than 0.005 mgm. per 100 cc.