- Has a negative pregnancy test (serum β-subunit hCG) immediately before study entry (ie, before the start of treatment or any other study procedure that could potentially harm the fetus). If obtaining the serum pregnancy test result will cause a delay in treatment, a subject may be entered on the basis of a negative urine pregnancy test sensitive to at least 50 mU/mL, pending results of the serum pregnancy test. Subsequently, if the result of the serum test is positive, the subject must be discontinued from study drug, and every attempt must be made to follow such subjects to term.