How to take Valtrex. Treatment with valacyclovir should be started as soon as possible after the first appearance of symptoms (such as tingling, burning, blisters). This medication might not be as effective if you first start taking it 1 or 2 days after the start of your symptoms. Take each dose with a full glass of water. Drink plenty of water while you are taking Valtrex to keep your kidneys working properly. Shake the oral suspension (liquid) well just before you measure a dose. To be sure you get the correct dose, measure the liquid with a marked measuring spoon or medicine cup, not with a regular table spoon.