Which anti-TB drug does not cause QT prolongation?

Cycloserine is the correct answer because it is not associated with QT prolongation, which is a critical consideration when using certain anti-tuberculosis medications. QT prolongation can lead to serious cardiac issues, including arrhythmias, making it essential to avoid drugs that have this side effect in patients who may already be at risk.

In contrast, Bedaquiline and Delamanid, both newer anti-TB agents, have been shown to cause QT prolongation as a side effect. These medications require careful monitoring of the QT interval during treatment, especially in patients with pre-existing heart conditions or those on other medications that can also prolong the QT interval. Clofazimine, while primarily used for leprosy, is used in some multi-drug resistant TB regimens and is also known to potentially cause QT prolongation.

Thus, among the choices provided, Cycloserine stands out as the option that does not contribute to this particular cardiac risk, making it a safer choice regarding the concern of QT prolongation.