An Oklahoma judge has struck down a law that limited the use of abortion drugs, ruling that the law was unconstitutional since it did not cover other medications.

Last year, the Oklahoma Legislature passed House Bill 2684, which placed restrictions on the use of abortion drugs, including one under the brand name Mifeprex. It was subsequently signed into law by Gov. Mary Fallin on April 22, 2014.

On Monday, US District Judge Patricia Parrish said she found the law unconstitutional.

The judge's decision infuriated Oklahoma's Republican lawmakers who have enacted a series of abortion restrictions. They immediately vowed to appeal the case.

"It is disappointing to see a judge strike down this law which was written by the legislature to specifically comply with the Supreme Court's guidance on this important issue," said Governor Fallin.

Under the law, the abortion drugs will have to be administered under the US Federal and Drug Administration approved dosage. It prohibited off-label use.

The Oklahoma law also banned medication abortions after 49 days of pregnancy that forces women to undergo surgical abortion.

In using Mifeprex, the FDA protocol states that a patient takes 600 mg of mifepristone orally at her doctor's office and return to the health centre 48 hours later to take 400 micrograms of misoprostol. The patient returns 14 days later for a follow-up visit.

Parrish issued her ruling following a suit filed on behalf of Reproductive Services, a nonprofit reproductive healthcare facility in Tulsa, and the Oklahoma Coalition for Reproductive Justice.

The two parties serving as plaintiffs in the case argued that the law prohibited off-label use of abortion-inducing drugs "purposefully and unconstitutionally, which limited non-surgical abortion options in Oklahoma."

They likewise claimed that the law forced doctors to treat women seeking abortions with outdated and less safe methods.

Under the regimen of Reproductive Services, a medication abortion patient takes 200 mg of mifepristone at the clinic and then takes 800 micrograms of misoprostol about six to 24 hours later at home or any location.

Reproductive Services and the Oklahoma Coalition for Reproductive Justice said the law is "an unconstitutional intrusion on women's reproductive rights that will harm women's health and well-being."

Nancy Northup, president and CEO of the Center for Reproductive Rights, said "today's ruling affirms that Oklahoma politicians cannot single out women for discrimination simply because they don't agree with their healthcare decisions."

However, the supporters of the law said the restrictions were made precisely to protect the health and safety of women.

They pointed out that Ohio, Texas and North Dakota have similar laws restricting abortion-inducing drugs, according to the Guttmacher Institute, which tracks reproductive health policy.