ViTrue's social media index aims to calculate a brand's share of voice by applying algorithms to conversations on various social networking, blogging, micro-blogging, photo and video sharing sites. The iPhone, for instance, topped its list of the top 100 social brands in 2008.

Pharmaceutical companies have been reluctant to embrace social media for fear of running afoul of FDA regulations that govern the advertising and promotion of prescription drugs. No pharma companies or drug brands made ViTrue's top 100 list last year.

Among the pharmaceutical giants, Pfizer, maker of well-known drugs like Viagra and Celebrex, was the top social brand with about 12% share of voice within the category. Pfizer was trailed by Johnson & Johnson and Novartis, each with almost 7%, with others well below 5%.

"Pfizer, Johnson & Johnson and Novartis are off to a solid start, but have a ways to go as it is a low base compared to more social brands like Coke, Disney and McDonald's," wrote ViTrue CEO Reggie Bradford in a blog post Monday. But it's likely that Big Pharma will remain mostly on the social media sidelines without more explicit guidelines from the FDA.

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