[M = tramadol, M1 = O-demethyl tramadol]

Figure 1: The impact of postmenstrual age (PMA) and CYP2D6 activity score on the plasma log M/M1 values is illustrated in neonates and young infants with an CYP2D6 activity score of either <2 or ≥ 2. The lower the log M/M1 value, the higher the phenotypic CYP2D6 iso-enzyme activity. There is an PMA-dependent effect and a polymorphism dependent effect (CYP2D6 activity score of <2 or ≥ 2) [8].