Prevention of HIV-infection

A method of maintaining a blood plasma level of 4-1000 ng/ml of 4-[[4-[[4-(2-cyanoethenyl)-2,6-dimethylphenyl]amino]-2-pyrimidinyl]-amino]benzonitrile, the E isomeric form thereof or the Z-isomeric form thereof in an individual at risk of being infected with HIV-1, comprising

• subcutaneously or intramuscularly injecting a solution into the individual, intermittently at a time interval of at least one week, wherein said solution comprises:
• sterile water;
• a solubilizer or a surfactant;
• and
• a dose, calculated on a basis of 0.2 mg/day to 50 mg/day of the time interval, of 4-[[4-[[4-(2-cyanoethenyl)-2,6-dimethylphenyl]amino]-2-pyrimidinyl]-amino]benzonitrile, the E isomeric form thereof or the Z-isomeric form thereof;
• or a pharmaceutically acceptable acid-addition salt thereof;
• wherein the blood plasma level is maintained over the time interval.