The U.S. Food and Drug Administration on Friday took steps to restrict what pharmaceutical ingredients large compounding pharmacies can use to manufacture drugs in bulk that do not go through the agency's approval processes.

The agency issued draft guidance that officials said prioritized the use of FDA-approved drugs over more risky, custom-made medicines produced in bulk by certain compounding pharmacies for hospitals and doctors' offices.

It marked the latest effort to regulate the industry following a fungal meningitis outbreak in 2012 linked to tainted drugs made in bulk by a compounding pharmacy that sickened 793 people, including 76 who died.

The guidance, if finalized, would limit the raw substances that large compounding pharmacies known as "outsourcing facilities" can use to make medicines in bulk that do not go through the FDA safety review process.

The FDA said it would only allow a raw substance to be used if a clinical need was established showing why an FDA-approved drug could not be used to make a compounded medication by, for example, diluting or crushing it.

"The safest alternative is always an FDA approved product," FDA Commissioner Scott Gottlieb said.

Gottlieb said he expected the number of substances that can be used will shrink from the nearly 200 currently permitted under an interim policy.

Compounding traditionally involves mixing tailored doses for particular patients to address specific needs, such as removing a dye to treat someone with an allergy.

By 2012, the practice had mushroomed, with some pharmacies selling thousands of doses of regularly used mixtures for physicians to keep for future use.

The outbreak tied to Massachusetts-based New England Compounding Center prompted Congress in 2013 to pass a law aimed at bringing under FDA oversight more compounding pharmacies typically regulated by states.

It established "outsourcing facilities" that could register with the FDA. Those roughly 70 facilities can sell products in bulk without individual prescriptions while following federal manufacturing standards.

The FDA was required to establish a list of substances those facilities could use for bulk compounding that met a "clinical need" but it has yet to finalize one.

Under an interim policy, it allowed the use of substances that compounders could nominate for eventual inclusion on the list that had no major safety issues.

That policy prompted a lawsuit in October by drugmaker Endo International Plc, who claimed the FDA was authorizing the bulk compounding of hundreds of drugs without proper evaluation.