A federal judge in Tennessee has declined to certify two classes in an antitrust case accusing a subsidiary of Pfizer Inc. of conspiring to keep cheaper generic versions of its Skelaxin muscle relaxant off the market. In Thursday’s 67-page decision, U.S. District Judge Curtis Collier in Chattanooga found the cases brought on behalf of end payers and indirect purchasers of the drug were inappropriate for class treatment.

Kaye Scholer represents Pfizer’s King Pharmaceuticals unit in the litigation and Munger, Tolles & Olson represents codefendant Mutual Pharmaceuticals.

Plaintiffs first filed suit in January 2012 accusing King and Mutual of conspiring to force them to overpay for Skelaxin by delaying the entry of cheaper generic versions into the market. Plaintiffs maintained that King and Mutual inappropriately delayed a patent litigation case against one another for five years in order to maintain outward appearances as adversaries to the public and regulators, while conspiring to keep versions of the branded muscle relaxer off the market.

The cases were transferred to Collier by the Judicial Panel on Multidistrict Litigation. In April 2012, Collier subdivided them into three classes: direct purchasers primarily consisting of wholesalers who bought drugs directly from the defendants; indirect purchasers mainly made up of retail pharmacies who purchased Skelaxin for resale; and end payers, which include funds and insurance companies that provided reimbursement for Skelaxin or its generic equivalent.

Collier denied the defendants’ motion to dismiss in May, finding that the plaintiffs had alleged sufficient facts to let their antitrust claims proceed. But on Thursday he declined to certify the indirect purchaser and end payer classes. (Lawyers for the direct purchasers, headed up by Thomas Sobol at Hagens Berman Sobol Shapiro, previously asked the judge to stay their class certification motion after revealing in November that they were in settlement discussions with defendants. No settlement papers had been filed as of Friday. Sobol could not be reached for comment.)

Collier found it would be difficult to figure out who actually bore the brunt of any potential overpayment in the end payer class, which includes pharmaceutical benefit managers that many health care plans use to pay for prescription drugs, along with insurers and individual consumers. “The individualized fact-finding required to shape the proposed class is inconsistent with class treatment,” he wrote. To see just how complicated it would be to unravel just who paid what for any particular prescription, check out the graphic Collier included in his decision.

Kaye Scholer’s Saul Morgenstern, who argued the class certification motion for King, told us he thinks Collier’s ruling is an important class certification decision in the wake of the U.S. Supreme Court’s decision in Comcast v. Behrend, which dealt with whether damages must be shown to be applicable classwide. Collier is “taking a deep dive into the mechanics of this industry,” says Morgenstern. “It’s an extremely complicated industry, and it just doesn’t lend itself to the blunt instrument of class litigation.”

James Stranch III at Branstetter, Stranch & Jennings, who argued the class certification motion for the end payers, said he and his cocounsel had yet to decide on their next steps, but he thinks they’ll likely ask to make an interlocutory appeal to the Sixth Circuit. “At first blush it appears that [the judge] did not apply the applicable law in the Sixth Circuit,” he said. “His decision would indicate that no one has a cause of action,” Stranch said.

As to the indirect purchasers, Collier found that he must apply the law of the state where the injury occurred, not Tennessee’s, as plaintiffs lawyers argued. “Indirect purchasers primarily placed their eggs in the nationwide-Tennessee-law basket and gave this issue short shrift,” Judge Collier wrote in declining to certify the indirect purchaser class.

Hausfeld’s Brent Landau, who argued the class certification issue for the indirect purchasers, wasn’t immediately available Friday.

Rohit Singla of Munger Tolles, who represents Mutual, directed us to a company spokeswoman, who declined to comment.