A process for preparing a particle comprising a co-precipitate surrounding a neutral hydrophilic carrier, said process comprising spraying an organic solution on a neutral hydrophilic carrier, said solution comprising at least one triazine or pyrimidine active ingredient having HIV inhibiting properties, one surface active agent, and one hydrophilic polymer, wherein the spraying of whole of the solution occurs in at least two separate steps, each of these steps followed by a grinding step of the product obtained at the end of the preceding step.