Giving pyrimethamine can lead to folate deficiency, which is the kind of shortfall 6s-5-Methyltetrahydrofolate [Bio-Active Folate] is meant to address. The leaflet lists pyrimethamine among the causes of folate deficiency, and it doesn't say anything more about the two medicines together.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.