Unfortunately, I don't think the clinical hold on IDX-184 -- the company's lead drug and the key to investor confidence -- will be easy to remove. That means Idenix will likely be dead money near-term.

Here's why: FDA's concerns stem from a theoretical connection between the Idenix and Bristol-Myers compounds. Idenix hasn't seen any clinical cardiovascular toxicity or preclinical warning signs thus far, which makes it hard to reassure regulators that the risks are manageable. As the saying goes, it's difficult to "disprove a negative."

FDA has asked Idenix for new data, including preclinical studies and cardiac evaluations of existing patients. The company plans to submit this information by year-end, which means that investors should expect a response -- and, perhaps, a path forward -- during the first quarter of 2013.

FDA also wants Idenix to propose additional monitoring of IDX-184-treated patients for signs of cardiovascular toxicity in any new studies, but it's unclear which metrics would be useful. The company has started to explore a potential biomarker for cardiovascular toxicity -- the creatively named N-terminal prohormone of brain natriuretic peptide, or NT-proBNP -- but the impact of other drugs on NT-proBNP levels in hepatitis C patients makes definitive interpretations difficult.

Idenix is in a tough spot, and it's hard not to empathize with management. Nonetheless, until Bristol-Myers determines what caused the side effects associated with BMS-094, I don't foresee an expeditious path forward. Idenix does have other drugs in development, including the promising NS5A inhibitor IDX-719, but these will likely be overshadowed by the clinical hold on IDX-184. Given the potential for-tax loss selling as we approach year-end and the risk that the clinical hold on IDX-184 could remain unresolved until at least mid-2013, prudence dictates that investors wait on the sidelines for now.

Disclosure: Sadeghi has no positions in any of the stocks mentioned in this article.

Follow Nathan Sadeghi-Nejad on Twitter.
Nathan Sadeghi-Nejad has 15 years experience as a professional health-care investor, most recently as a sector head for Highside Capital. He has worked on the sell side (with independent research boutiques Sturza's Medical Research and Avalon Research) and the buyside (at Kilkenny Capital prior to Highside). Sadeghi-Nejad is a graduate of Columbia University and lives in New York. You can follow him on Twitter @natesadeghi.

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