A number of individuals have filed federal lawsuits alleging that their use of the cholesterol-lowering drug Lipitor caused them to develop Type 2 diabetes. The lawsuits have been consolidated in a federal district court in South Carolina.

When large numbers of cases are consolidated in one court under federal rules governing multidistrict litigation, a single case is chosen for trial. That case, known as the “bellwether,” is chosen because it is representative of the other cases awaiting trial. The outcome of the bellwether case may encourage settlement of the remaining cases. It also helps the other litigants assess the risks and costs of taking their cases to trial.

Products liability cases against drug manufacturers necessarily hinge on expert testimony. The judge presiding in the multidistrict Lipitor litigation recently concluded that one of the expert witnesses designated by the plaintiffs in the bellwether case would not be allowed to testify that Lipitor causes Type 2 diabetes.

The Hempstead Case

Juanita Hempstead’s case was chosen as the bellwether. Hempstead was given a prescription for Lipitor in March 1998. She started taking it in June 1999 but did not take it consistently until July 2000. Her lipid levels (including her level of total cholesterol) were higher than normal before she began regular use of Lipitor. Her blood glucose level was normal when it was tested in 1999.

In 2002, Hempstead’s lipid levels were normal. Her glucose level, however, was abnormal. It was in a range that is classified as pre-diabetic. In 2003, Hempstead stopped taking Lipitor for three weeks because she was experiencing abdominal pain. At the end of the three weeks, her lipid and glucose levels were higher than they were in 2002. She resumed use of Lipitor and, three months later, her lipid levels returned to normal.

In February 2004, Hempstead was hospitalized for colitis. Her glucose reading at that time was in the diabetic range. Three months later, her glucose level was substantially higher and she was diagnosed with new-onset diabetes. Hempstead’s weight apparently increased steadily between 1998 and 2004.

Causation

Hempstead was required to prove both general and specific causation. To prove general causation, she needed evidence to establish that Lipitor is capable of causing diabetes. To prove specific causation, she needed evidence that Lipitor actually caused her diabetes.

The district court took note of cases that require no proof of specific causation if studies of general causation establish that taking a drug at least doubles the risk of sustaining the injury for which the plaintiff is suing. Those cases hold that if most people who take a drug experience the harm that the plaintiff experienced, no additional proof of causation is necessary, at least if the plaintiff’s characteristics and use of the drug were similar to those of the subjects who participated in the study that established the risk.

Studies cited by Hempstead’s experts established that taking Lipitor increases the risk of developing diabetes by a factor of 1.6. Since that is less than a doubling of risk, Hempstead was required to prove that Lipitor actually caused her diabetes. She relied on Dr. Elizabeth Murphy to prove specific causation.

Daubert Analysis

The court based its decision on Rule 702 of the Federal Rules of Evidence, as interpreted by the Daubert decision. That rule requires the trial judge to assure that an expert’s testimony will be both relevant and reliable. The reliability of scientific opinions is measured by whether the expert reasonably applied reliable principles and methods to sufficient facts or data.

The court noted that in its role as gatekeeper, it must not substitute its own view of expert opinions for the view that a jury could reasonably take. At the same time, the court has an obligation to protect the integrity of the jury’s decision by assuring that expert evidence, which has the potential “to be both powerful and quite misleading,” is based on a reliable methodology.

Dr. Murphy is a Professor of Clinical Medicine and the Chief of the Division of Endocrinology at San Francisco General Hospital. She has an M.D. from Harvard and a Ph.D. in biochemistry from Oxford. Her credentials to testify as an expert were clear, so the question was whether her opinion that Hempstead’s diabetes was caused by Lipitor was rooted in a reliable methodology.

The court characterized Dr. Murphy’s opinion as being based on (1) the fact that Lipitor increases the risk of diabetes (general causation) and (2) the fact Hempstead developed diabetes after taking Lipitor. Dr. Murphy’s deposition testimony disclosed no fact other than the temporal relationship between using Lipitor and the onset of diabetes that supported her opinion of a causal relationship between the two.

The court faulted Dr. Murphy for failing to rule out other risk factors that might have caused the onset of Hempstead’s diabetes, including her weight gain and a corresponding increase in her body mass index (BMI). Hempstead’s family history, age, and struggle with hypertension were also factors that could have caused her diabetes. The court concluded that Dr. Murphy’s opinion was unreliable because she did not determine whether Hempstead would have developed diabetes without taking Lipitor and did not compare the magnitude of the risk of diabetes onset associated with taking Lipitor to the magnitude of the risk that existed if Hempstead had not taken Lipitor.

Court Excludes Expert Opinion

It may be that the public interest would best be served by holding drug companies accountable for increasing a patient’s risk of contracting a disease, even when it cannot be established that the patient fell within the significant percentage of drug recipients whose disease was caused by the drug rather than the percentage who would have contracted the disease anyway. That, however, is not the law that governed the District Court’s decision.

Because Dr. Murphy’s testimony did not move beyond general causation to establish a specific link between Hempstead’s use of Lipitor and her development of diabetes, the district court barred Dr. Murphy’s testimony on the ground that her opinion about specific causation had no scientific basis. Whether Hempstead’s case will be able to move forward, and how the ruling will affect other Lipitor cases, are issues that will likely be decided in the coming weeks.