Part of the phenacetin by ethylation of paracetamol process involves an aqueous base extraction intended to remove unreacted paracetamol (addition 7 in Figure 11) While this step would be expected to minimise the amount of paracetamol starting material present, some residual paracetamol impurity. https://www.benzocainesupplier.com/understanding-lidocaine-in-the-uk-usage-availability-and-legal-aspects