This recent decision by the US Supreme Court may significantly change the patent protection available in the US for personalised medicine, and possibly diagnostic methods in general. The patent in issue covered a method of establishing a personalised drug dose for a particular patient. Treatment with certain drug types is complicated by the fact that they are broken down in the body to create toxic metabolites. The rate at which this happens varies in different people, making it hard to establish an appropriate dose of the drug. The inventors of the patent had determined the levels of metabolite in the blood which reflected a drug dose which was effective while avoiding toxic side effects.The patent claimed a method of optimising the therapy of an autoimmune disease by (a) administering a drug which produces a specific metabolite in the body, and (b) determining the level of the metabolite in the body, wherein a level of metabolite below a specific value indicates a need to increase the level of drug administered, and a level of metabolite above a specific value indicates a need to decrease the level of drug administered.The Supreme Court held that the claims were not eligible for patent protection because they amounted to no more than an attempt to claim a law of nature. It is well established in US jurisprudence that laws of nature, natural phenomena and abstract ideas are not patent-eligible.The Court decided that the relationship between the metabolite in the blood and the likelihood that the drug will be toxic or ineffective represented a law of nature which is not in itself patentable. They went on to consider whether the additional steps in the claim could confer patent eligibility. They considered the steps to be (a) an ‘administering’ step telling the user to administer the drug; (b) a ‘determining’ step telling the user to determine the metabolite levels, and (c) a ‘wherein’ step which describes the metabolite concentrations above which toxicity is likely and below which the drug is unlikely to be effective.These steps were deemed not to confer patent eligibility, even in combination, because they were simply routine activities already engaged in by the scientific community. In essence, the Court considered that the steps amounted to nothing more than instructing the user to apply the law of nature stated in the claim.The USPTO has issued a Memorandum to provide Examiners with practical guidance in applying the decision. They state that ‘Examiners must continue to ensure that claims, particularly process claims, are not directed to an exception to eligibility such that the claim amounts to a monopoly on the law of nature, natural phenomenon, or abstract idea itself. In addition, to be patent-eligible, a claim that includes an exception should include other elements or combination of elements such that, in practice, the claimed product or process amounts to significantly more than a law of nature, a natural phenomenon, or an abstract idea with conventional steps specified at a high level of generality appended thereto’. The USPTO is continuing to study the decision and is developing further detailed guidance.The practical consequences of this decision are that companies filing patent applications in the field of medical diagnostics are likely to face enhanced difficulties in obtaining US patents with claims based on biological correlations, and the validity of US patents with claims based on biological correlations may now be questionable under 35 U.S.C. § 101.   Contact: Béatrice Holtz   