Blood transfusions must be given with care because they have the potential to cause adverse reactions in rare cases. The most serious risk of transfusion is immediate destruction of red blood cells. In horses, a complete match is rarely possible, and even when donor and recipient are compatible, red blood cells survive only 2 to 4 days. Other rare potential complications include fever and the spread of infections.
That's why the blood test should be done every day after the procedure for one week at least.
And there is no need to give any medication unless any complications happened, then the medicines depend on the completion it self.