My son just started taking Atenolol for POTS tachycardia , His blood pressure this morning was 110/66, after he took his first 12.5 dose, this evening after the second dose, his blood pressure had dropped to 89/52, and while he was sleeping I just took it and it is 85/51, He is 9 years old, and weighs about 65lbs, and is 52inches tall.