- Female patients with reproductive potential must have a negative serum pregnancy test within 7 days prior to the start of the trial. A woman with reproductive potential is defined as one who is biologically capable of becoming pregnant. Patients who are not surgically sterile or postmenopausal must agree to use a medically acceptable and highly effective method of birth control for the duration of the study and to continue after the end of CHR-2797 treatment for a further 3 months (female patients) or for a further 6 months (for male patients and their partners). A highly effective method of birth control is defined as any method that results in a low failure rate, including implants, injectables, some intra-uterine devices (IUD's), sexual abstinence, and vasectomy/ sterilization. Sexually active males and females using oral contraceptive pills should also use barrier contraception. Although there is no reason to believe that the use of CHR-2797 has an effect on the pharmacokinetics of hormonal contraceptives, this has not yet been proven.