The first biosimilar drug was approved by the Food and Drug Administration for use in the United States.

The drug, called Zarxio, is the first to pave the way for a less expensive alternative. It is a close copy of an existing medication called Neupogen, made by Amgen. Zarxio, produced by Sandoz, is used to help prevent infections in cancer patients receiving chemotherapy.

The drug was initially approved in Europe in 2009 as Zarzio. Biosimilars, approximate copies of drugs in a class known as biologics, however, were not allowed for use at that time in the United States.

An expert panel recommended that the FDA approve the drugs back in January and the agency announced on Friday that it had taken their advice, according to the New York Times.

The approval opens the door to a new class of potentially inexpensive lifesaving drugs. Biologic drugs, made using living cells not synthesized from chemicals, are amid the world’s most expensive medications.

In most cases, brand-name drugs ultimately lose their patent protection and open up the market to generic products at a lower cost. But biologics have been shielded from the rivalry of cheaper versions so far.

When biologic drugs were first created in the 1980s, they were considered so specialized that producing generic versions seemed impossible. Luckily, science has advanced.

Drug companies have begun developing close copies seeking FDA approval. This initiated a spark in competition and lower prices for this critical class of drugs.

Biosimilars are about a third cheaper than brand-name biologic drugs. Some experts forecast that the discounts could be even sharper, possibly reaching up to 90 percent.

Express Scripts, the nation’s largest manager of prescription drug benefits, approximates that Zarzio’s introduction in the United States could save billions in drug costs over the next 10 years.

Amgen claims that Sandoz did not follow the rules in terms of informing them in advance of its plans for the drugs. Sandoz has denied this, but a hearing is scheduled for March 13 on Amgen’s request for a preliminary injunction. Sandoz has said that they will not start selling Zarxio until a decision is made on the injunction, or April 10, whichever comes first.

One challenge experts foresee is the fact that manufacturers of typical generic drugs do not market their products directly, but instead, rely on pharmacists to offer the substitution of the generic for a brand-name drug.

But this usual replacement cannot happen with biosimilars yet. The makers of biosimilars most likely will have to ask doctors to prescribe their drug and coax insurers to insist on the use of less expensive biosimilars.