- Smoking History: Current or former cigarette smokers with a history of cigarette smoking of greater than 10 pack-years [number of pack years = (number of cigarettes per day/20) x number of years smoked (e.g., 20 cigarettes per day for 10 years, or 10 cigarettes per day for 20 years]. Former smokers are defined as those who have stopped smoking for at least 6 months prior to Screening Visit