Biquin Injection is Quinapyramine Sulphate mixed with Quinapyramine Chloride active against Trypanosoma brucei, T. Congolenses, T. equinum, T.equiperdum, T.evansi, T. simiae and T. vivax. Quinapyramine Sulphate is soluble in water where as Quinapyramine Chloride is almost insoluble. The Sulphate is rapidly absorbed giving an initial high blood level; the Chloride is more slowly released from a depot formed at the injection site. Although the Sulphate alone has some prophylactic properties a much more prolonged effect is obtained with the mixed salts. The Chloride alone is unsuitable as a prophylactic for general use. Under field conditions an initial sterilizing effect of the trypanocide is a necessary property of a prophylactic inoculation. The period that may be allowed between prophylactic treatments is dependent upon a number of factors including the strain and species of trypanosome concerned, the density of the vector population and the infection rate of the flies themselves, which is generally between two to three months. The total length of time for which a prophylactic regime may be maintained successfully varies similarly and can only be determined satisfactorily by observation of the treated stock.