Twice weekly isoniazid and rifampin treatment of latent tuberculosis infection in Canadian plains aborigines

Six months of twice weekly directly observed isoniazid and rifampicin treat ment of latent tuberculosis (TB) infection was implemented to improve the o utcome of treatment. A total of 591 infected aborigines without previous tu berculosis or treatment of latent TB infection received twice weekly isonia zid and rifampicin for 6 mo from 1992 to 1995. The outcome was compared wit h 403 infected aborigines without previous tuberculosis or treatment of lat ent TB infection who received self-administered isoniazid daily for 1 yr fr om 1986 to 1989. Of patients, 487 (82%) completed the twice weekly 6-mo reg imen compared with 77 (19%) who completed the daily 12-mo regimen. The main reason for Incomplete treatment was default. Both groups were followed ove r a 6-yr period. The rate of tuberculosis in the twice-weekly isoniazid and rifampicin-treated patients was 0.9/1,000 patient-years compared with 9/1, 000 patient-years in the daily isoniazid-treated patients. The rate of side effects was higher for directly observed treatment patients, 136/1,000 pat ient-years of drugs, compared with 39/1,000 patient-years for self-administ ered treatment patients. Life-threatening side effects such as skin allergi c reactions and hepatitis were the same in both groups. A regimen of 52 dos es of directly observed twice weekly isoniazid and rifampicin is an effecti ve and well-tolerated regimen to improve the outcome of the treatment of la tent tuberculosis infection in a population with a high rate of default wit h daily self-administered isoniazid.