WHO estimates that up to half a million new cases of multidrug-resistant tuberculosis (MDR-TB) occur worldwide, each year. Current treatment regimens for MDR-TB present many challenges: treatment lasts 20 months or more, requiring daily administration of drugs that are more toxic, less effective, and far more expensive than those used to treat drug-susceptible TB. Globally, less than half of all patients who start MDR-TB therapy are treated successfully.