the dosage of tetracycline to treat acne would be more dependent on the type and severity of the acne than his weight. at 150 pounds your teen can take up to a full adult dose from 250 mg 4 times per day or even higher. some medical providers treating acne will only give it once or twice per day again depending on the current severity of the acne and the response to treatment. i don't typically use tetracycline; i use a similar drug called doxycyline that is much easier on the stomach and can be taken without regards to food.
what is the proper dose of tetracycline used for acne for a healthy male approx. 150 pounds