Fatal meningitis outbreak will go down as one of the biggest drug disasters in American history. (Hannah Foslien/AP)

Drug compounding — the custom-mixing of drugs for specific patients — predates the industrial production of pharmaceuticals, which started in the late 1800s. Government regulators have let the practice persist for a few reasons. The most often cited is the need for some patients to use medicines free of dyes, binders and other additives

In the last two decades, industrial-scale compounding has emerged as a big — and in some eyes essential — source of drugs.

Companies such as New England Compounding Center, the now-closed company at the heart of the fatal meningitis outbreak, make products that are virtual copies of ones produced by drug companies.

In some cases, these “compounding pharmacies” start with raw materials. Sometimes they repackage finished drugs they get from drug companies. Either way, the product is hard to visually distinguish from what one might buy from Merck, Pfizer or GlaxoSmithKline.

NECC’s steroids were sold in stoppered glass vials, just like a drug company’s. Many clinics bought compounded drugs in bulk, as they do from drug manufacturers. Until the latest outbreak — which has sickened 696 people and killed 45 — many physicians considered the products to be interchangeable with manufactured drugs.

Here are basic steps a compounder could follow to make a drug.

But they aren’t.

Compounded drugs aren’t FDA-approved. Compounders aren’t held to the same inspection standards as drug companies. The FDA rarely inspects the production sites unless there’s a problem with, for example, the drugs’ sterility or potency. Instead, state pharmacy boards, whose oversight and expertise vary from place to place, are the chief regulators of compounding pharmacies.

Even if no more cases develop, the current outbreak will go down as one of the biggest drug disasters in American history, rivaling the 1955 “Cutter Incident,” in which 200 children were paralyzed and 10 killed by improperly made polio vaccine.

In coming months, Congress is likely to set new rules for what compounding pharmacies are allowed to produce.

Making sterile liquids for injection deep into the body may soon be off the list. Making injectable steroids almost certainly will be. The reason is simple: They’re too hard to make, and too dangerous when made badly.

“This is very challenging to get right,” said Niall Condon, vice president of manufacturing operations at Pfizer Global Supply, which makes FDA-approved methylprednisolone acetate. “Equipment, materials and people — everything has to be done well.”

James Agalloco, a consultant to drug companies on production issues, agreed.

“To do this right, you have to spend more money than these compounders are typically willing to spend,” he said.

“Can compounders make sterile injectables safely? My personal opinion is no,” said David Gaugh, senior vice president for science at the Generic Pharmaceutical Association. “Would I let this type of product be injected into a family member? The answer is: I wouldn’t.”