The dose-response theory requires a toxic tort plaintiff to establish “scientific knowledge of the harmful level of exposure to a chemical plus knowledge that the plaintiff was exposed to such quantities” to meet his or her threshold burden of proof.  McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1241 (11th Cir. 2005) (citing Allen v. Pennsylvania Eng’g Corp., 102 F.3d 194, 199 (5th Cir. 1996).  See also Mitchell v. Gencorp, 165 F.3d 778, 781 (10th Cir. 1999) (quoting Wright v. Willamette Indus., Inc., 91 F.3d 1105, 1106 (8th Cir. 1996)).  If a plaintiff does not present expert testimony sufficient to sustain this burden, the plaintiff’s case is vulnerable to attack via a motion in limine, motion for summary adjudication or even an appeal from an adverse verdict.  Accordingly, defense counsel should assess, as early as possible, the suitability of expert testimony offered to support the plaintiff’s case.

On a basic level, the dose-response relationship is “[a] relationship in which a change in amount, intensity, or duration of exposure to an agent is associated with a change – either an increase or decrease – in risk of disease.”  McClain, 401 F.3d at 1241-1242.  Any expert “who avoids or neglects this principle of toxic torts without justification casts suspicion on the reliability of his methodology.”  Id., 401 F.3d at 1242.  Accordingly, that expert’s methodology is susceptible to a Daubert challenge.  See Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 125 L. Ed. 2d 469, 113 S. Ct. 2786 (1993).

For instance, in McClain, the U.S. Court of Appeals for the Eleventh Circuit reversed a jury verdict in a products liability action against Metabolife International, Inc. where it found that the trial court erroneously admitted expert testimony purporting to establish causation between the herbal weight-loss supplement at issue and the plaintiffs’ medical conditions.  McClain, 401 F.3d at 1236.  While the plaintiffs offered testimony regarding the amount of the supplement ingested, their expert could not provide any opinions about “the general dose-response levels for Metabolife’s toxicity, i.e., the dose or level of exposure at which it causes harm.”  McClain, 401 F.3d at 1241.  Even though an expert need not provide precise numbers to substantiate the dose-response relationship, “the link between an expert’s opinions and the dose-response relationship is a key element of reliability in toxic tort cases.”  Id., 401 F.3d at 1241, Fn. 6.

The court’s analysis in McClain figures prominently in a recent products liability case in the Eleventh Circuit decided on September 11, 2014.  In Chapman v. The Procter & Gamble Distributing, LLC, 766 F.3d 1296 (11th Cir. 2014), the plaintiffs brought claims against several Procter & Gamble entities alleging that an ingredient in Fixodent, a denture adhesive, caused one of the plaintiffs to suffer from myelopathy, a neurological condition or spinal-cord disorder that affects the upper and lower extremities.  The plaintiffs’ claims did not survive summary judgment at the trial court level and the Eleventh Circuit affirmed that ruling on appeal.  Id.  The Chapman court discussed the importance of the dose-response theory as follows:

Recognizing all substances potentially can be toxic, the [trial] judge noted “ ‘the relationship between dose and effect (dose-response relationship) is the hallmark of basic toxicology,’ ” and “ ‘is the single most important factor to consider in evaluating whether an alleged exposure caused a specific adverse effect.’ ” In re Denture Cream Prods. Liab. Litig., 795 F. Supp. 2d at 1351-52 (quoting McClain, 401 F.3d at 1242). The judge noted, however, neither the Chapmans’ general-causation experts “nor the articles on which they rely determine how much Fixodent must be used for how long to increase the risk of a copper-deficiency, or for how long a copper-deficiency must persist before an individual is at an increased risk of developing a myelopathy.” Id. at 1352.

Without critical evidence regarding reliable methodologies for establishing causation, the plaintiffs’ claims were doomed.  Chapman, 766 F.3d 1296.

The McClain analysis of the dose-response theory is influential in the Eleventh Circuit and beyond, having also been cited by U.S. District Courts in the Second, Third, Sixth, Eighth, Ninth, and D.C. Circuits and the Federal Claims Court.  See Second Circuit – Deutsch v. Novartis Pharms. Corp., 768 F. Supp. 2d 420 (E.D.N.Y. 2011), Colon v. Abbott Labs., 397 F. Supp. 2d 405; Third Circuit – Patrick v. FirstEnergy Generation Corp., 2014 U.S. Dist. LEXIS 43036 (W.D. Pa. Mar. 31, 2014); Sixth Circuit – Rose v. Matrixx Initiatives, Inc., 2008 U.S. Dist. LEXIS 110116 (W.D. Tenn. Dec. 9, 2008), Adams v. Cooper Indus., 2007 U.S. Dist. LEXIS 55131 (E.D. Ky. July 30, 2007); Eighth Circuit – Beylin v. Wyeth (In re Prempro Prods. Liab. Litig.), 738 F. Supp. 2d 887, CCH Prod. Liab. Rep. P18490 (E.D. Ark. 2010), In re Baycol Prods. Litig., 532 F. Supp. 2d 1029 (D. Minn. 2007); Ninth Circuit – Monroe v. Zimmer US Inc., 766 F. Supp. 2d 1012 (E.D. Cal. 2011), Henricksen v. ConocoPhillips Co., 605 F. Supp. 2d 1142, 78 Fed. R. Evid. Serv. (CBC) 857 (E.D. Wash. 2009), Lusch v. Matrixx Initiatives, Inc., 2007 U.S. Dist. LEXIS 72068, 74 Fed. R. Evid. Serv. (CBC) 880 (D. Or. Sept. 25, 2007), O’Hanlon v. Matrixx Initiatives, 2007 U.S. Dist. LEXIS 65655 (C.D. Cal. Jan. 3, 2007); D.C. Circuit – Arias v. DynCorp, 928 F. Supp. 2d 10 (D.D.C. 2013); Federal Claims Court – Graves v. Sec’y of HHS, 2010 U.S. Claims LEXIS 1037 (Fed. Cl. Sept. 21, 2010).  But see In re Zicam Cold Remedy Mktg., Sales Practices & Prods. Liab. Litig., 2011 U.S. Dist. LEXIS 79244 (D. Ariz. July 15, 2011) (criticizing the McClain court’s application of the “toxic dose” requirement in environmental exposure litigation in the context of a drug products liability action).

Challenging the reliability of an expert’s methodology where the dose-response relationship has been neglected can streamline the issues at trial in a toxic tort case and, in some instances, may obviate the need for trial.  Accordingly, an examination of the dose-response theory should be an early and recurring priority.