Note: The differences between the subjects may be in age, stage or severity of the disease, and prior drug treatment that some may have received. In such a crossover study, the patients are divided into two equal size groups, uniform with respect to age, body weight, sex, etc. The first group is given a specific dose of the product studied, while the second group is given a second product of proven clinical efficacy, containing the same active ingredient. After taking an appropriate number of blood samples from each individual and a washout period, the groups are reversed and the first group is given the product of proven clinical efficacy and the second is given the product being studied. This way each patient serves as his or her own control.