Case report on cycloserine serum levels after treatment with oral terizidone and oral cycloserine

A 24 year old man with multi-drug resistant pulmonary tuberculosis was treated with a regime that included terizidone and then cycloserine. Serum drug levels of cycloserine were higher on milligram equivalent doses of cycloserine. Guidance implies that terizidone should be considered bioequivalent to cycloserine, but this case illustrates that this cannot be presumed. Any reduction in neuropsychiatric side-effects with terizidone may be due to lower cycloserine exposure and thereby reduced anti-mycobacterial efficacy.