The Supreme Court split 4-4 on a narrow pre-emption case Monday, giving the green light to suits against Pfizer predecessor Warner Lambert.

With Chief Justice John Roberts sitting out the decision due to his ownership of Pfizer stock, the court was divided on whether or not to overturn a New York appeals court verdict allowing the suits, by Michigan residents who say they were harmed by Warner Lambert’s diabetes drug Rezulin, to proceed. At issue was a Michigan law barring suits against drug companies for FDA-approved products and an exception to that law, involving “fraud” claims, that contradicts Supreme Court precedent. The upshot: the cases against Warner Lambert can go forward, and while the non-decision establishes no precedent, it should make it easier for Michigan residents to sue drug companies for fraud in New York courts.

However limited the repercussions, the gridlock came as a surprise to many in the industry after the court’s resounding 8-1 decision in February that patients can’t sue medical device manufacturers over the safety and effectiveness of FDA-approved products. Writing for the majority in that case, Riegel v. Medtronic, Justice Antonin Scalia said. “Premarket approval is a ‘rigorous’ process” that should preempt state law.

Riegel v. Medtronic hinged on a specific statute pertaining to medical devices. For drugs and biologics, the key test of preemption, Wyeth v. Levine, goes before the court this fall. The case, in which Wyeth is challenging a Vermont ruling which awarded $6.8 million in damages to a woman injured by Wyeth anti-nausea drug Phenargan, could determine the viability of “failure to warn” claims, which constitute the bulk of tort suits against drug manufacturers.

The FDA has asserted that its decisions trump those of state courts, because companies cannot add warnings to labeling beyond those approved by the agency to guard against “overwarning” that might scare patients away from needed medications. “The plaintiff’s lawyers’ theory that FDA warnings are only a floor, not a ceiling, is blown out of the water if FDA says manufacturers are not permitted to put additional warnings in the label,” said. Richard Samp, chief counsel for the Washington Legal Foundation. Samp said the court has typically shown deference to federal agencies in similar cases, and that the Michigan and Medtronic cases offer little insight into how the court will handle Wyeth v. Levine.

If the court does uphold pre-emption, rendering “failure to warn” arguments moot, plaintiff’s lawyers will still have two avenues for product liability suits: defective design claims, asserting that the risk/benefit profile of a product was so lousy it should have never been manufactured, and negligent manufacture of a product of sound design.

The court has not yet set an argument date for Wyeth v. Levine, but it will likely be heard in October, with a decision in January or February, Samp said.