PharmAthene said today its SparVax® rPA anthrax vaccine program has been placed on clinical hold by the FDA, for reasons yet to be disclosed—the second such hold placed on the program in less than a year.

PharmAthene said that it was notified by the FDA of the hold and that the agency will send the company a letter providing details of the basis for the hold “within 30 days.”

The hold appears to concern the company’s Phase II clinical study for SparVax rPA, a next-generation recombinant protective (rPA) anthrax vaccine. Pharmathene said the Phase II study “has not enrolled any subjects to date, and accordingly there have been no adverse events reported.”

As late as last month, PharmAthene president and CEO Eric I. Richman said in releasing quarterly results that the company was on track to launch the Phase II trial of SparVax, “which we anticipate will begin by the end of the year.”

SparVax development had already been slowed by a an FDA clinical hold imposed in August 2012, and lifted in May; the agency requested PharmAthene provide additional stability data for both its engineering and GMP lots of U.S.-manufactured final drug product, as well as additional information about the intended stability indicating assays.

PharmAthene disclosed the latest clinical hold two weeks after saying December 2 that it had called off a planned merger with Theraclone Sciences, as well as a special meeting of PharmAthene stockholders set for Tuesday to formalize the transaction. PharmAthene did not state a reason for its about-face, which required the company to pay Theraclone a $1 million termination fee.

PharmAthene and Theraclone announced their merger August 1, without disclosing the price but trumpeting the deal as enabling the creation of a combined company focused on developing vaccines against infectious diseases and human monoclonal antibody drugs against cancer.

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