PURPOSE: The titled preparation of low toxicity that contains an adenine derivative or its salt.

CONSTITUTION: A compound of formula (R1, R2 are H, 1W3C alkyl; R3, R4 are halogen) or its salt such as 6-amino-9-(2-chloro-6-fluorobenzyl)purine is used as an active ingredient to give an antitoxoplasmatic for mammarians such as pigs, cats or dogs. The compound of the formula or its salt is diluted with a solid or liquid diluent, or not diluted, then made into an appropriate preparation such as a powder, a dust, granules, tablets, a solution, capsules or injection solution and given orally or parenterally. Or it is added to feed or drinking water and applied to mammarians. The dose is, when it is added to feed or drinking water, 0.001W0.5wt% as the compound of the formula.