Poor metaboliser

An individual who expresses a mutant metabolic enzyme, often as a result of a point mutation, where the enzyme has lower activity (higher K_M, lower V_max, or some combination of changes in K_M and V_max that reduce substrate turnover) versus one or more drugs. Alternatively, the individual may have an enzyme that is entirely inactive, such that a different enzyme may assume responsibility for the (less efficient) clearance of the drug.

Poor metabolisers may require lower drug doses than extensive metabolisers to achieve a similar steady state concentration with repeated dosing.