Pharmaceutical companies are learning that it is often not enough simply to bring a drug to market.  Regulators and insurers are also prodding the companies to develop tests to pinpoint which patients are most likely to benefit from a drug, thereby sparing other patients from needless side effects and expense.  The pressure has thrust drug and diagnostics companies into sometimes awkward partnerships aimed at developing such tests, which are called companion diagnostics. There were at least 25 such deals in 2010 and 15 in the first half of 2011, up from only seven in 2008, according to PricewaterhouseCoopers, a consulting firm. The US Food and Drug Administration (FDA) issued guidance to the industry on companion diagnostics in July, including its preference for having the test ready for approval at the same time as the drug. The following month, as if to show how it should be done, it approved two drugs and their accompanying tests.(NYTimes)