Harris County Attorney Vince Ryan has filed a federal lawsuit against 43 manufacturers of generic drugs he alleges have engaged in a price-fixing scheme that has cost taxpayers millions.

Ryan said the companies sought to limit competition and increased prices of at least 181 generic drugs, including those used to treat heart failure, seizures, bacterial infections, high blood pressure, epilepsy and asthma. The defendants include Teva Pharmaceuticals, Actavis Holdco, Morton Grove Pharmaceuticals and Mylan Inc.

“These prices skyrocketed at unprecedented rates, many by more than 1,000 percent,” Ryan said. “Since 2013, the county has paid $25 million for the generic drugs involved.”

Drug manufacturers are granted patents with a period of exclusivity, meaning their products can be sold at high prices during the initial years on the market. After that period ends, other manufacturers are allowed to make the same drug, and Ryan said prices should drop by 75 to 85 percent. Ryan alleged the firms conspired to make sure a drug has only one manufacturer, even when others are permitted, keeping prices high.

Clomipramine is one such drug, Ryan said. He gestured to a chart that showed how the price of the substance, used to treat obsessive-compulsive disorder, increased 3,482 percent over a four-year period.

Other drugs made by the accused manufacturers include the generic equivalents for Celebrex, Synthroid, Adderall, Lipoderm, Relafen and Prozac.

Teva Pharmaceuticals and Mylan Inc. did not respond to requests for comment.

The county attorney’s office is asking a judge to prohibit the companies from keeping prices high and order the firms to reimburse Harris County.

“We intend to hold these pharmaceutical companies accountable for one of the most egregious and massive price fixing conspiracies in the history of the United States,” Ryan said.

Ryan, who is seeking a fourth term, faces a difficult Democratic Party primary on Tuesday against Christian Menefee and Ben Rose.

The timing of the news conference on the eve of Election Day was coincidental, Ryan said, adding he had planned to make the announcement last week.

The county also sued a trio of insulin manufacturers in November, alleging the companies colluded to set artificially high prices for the medicine and other diabetic treatments. Ryan said that case is ongoing.

Two years ago, the county sued 21 pharmaceutical companies it said are manufacturing the painkillers fueling the nation’s opioid crisis.

zach.despart@chron.com