A year before people began dying of meningitis caused by a tainted drug from a compounding pharmacy in Massachusetts, the Food and Drug Administration worried that compounders across the country might be selling another substandard drug, one possibly made with unapproved Chinese ingredients.

But when the F.D.A. began seeking samples to test, the trade group representing compounding pharmacists went on the offensive. Instead of encouraging members to help the agency determine if the injectable drug, used to reduce the risk of premature birth, was substandard, the group tutored pharmacists on how to sidestep requests.

In an e-mail to members, the International Academy of Compounding Pharmacists suggested that they respond to any request for samples by saying, “We do not compound or distribute ‘samples’ of any of our prescription medications to anyone.” And if a compounded drug was on the premises, the trade group added, a pharmacist should say it was awaiting pickup by a patient.

A spokesman for the trade group said the instructions were intended to guard against unauthorized release of samples to corporate competitors and not to hinder the F.D.A. investigation. But the memo is emblematic of the industry’s frequent and often successful attempts to fend off regulators at a time when concerns are growing about the quality of compounded drugs and the uncertain provenance of their ingredients, some of which originate in China and flow through various repackagers and middlemen with little scrutiny, according to interviews with health experts and government records.