- Must refrain from the use of any methylxanthine-containing products, (e.g., chocolate bars or beverages, coffee, teas, or colas) from 48 hours before administration of study drug and during confinement, and when caffeine is allowed, must avoid excessive use of caffeine (i.e., no more than approximately 500 mg/day, as contained in 5 cups of tea or coffee or 8 cans of cola), during the entire study (from screening to end of study)