CH 3CH 3CH 3CH 3CH 2 CH 3CH 2 CH 3CH 3NH 2CH 3NHCOCH 2 NCH 2 CH 3NHCOCH 2 NHCH 3CH 3CH 2 CH 3NHCOCH 2 NHOCH 3CH 3NHCOCH 2 NH 2CH 3CH 3CH 2 CH 3CH 2 CH 3NHCOCH 2 NHHOHOCOOHNH 2CH 3HO NH 2CH 3CH 3Lignocaine4-Hydroxy-2,6-dimethylaniline2,6-DimethylanilineFurther
metabolitesFurther
metabolitesFurther
metabolitesFurther
metabolitesHydrolysisOxidation
DealkylationOxidationOxidationOxidationHydrolysisDealkylation4-Hydroxy-
2,6-xylidine3-Hydroxymonoethyl-
glycylxylidide3-Hydroxylignocaine GlycylxylidideMonoethylglycylxylidideFigure 2.5 An outline of the known metabolic pathways of the local anaesthetic lignocaineits site of action. A slow elimination process can result in a build-up of the drug
concentration in the body. This may benefit the patient in that the dose required
to maintain the therapeutic effect can be reduced, which in turn reduces the
chances of unwanted side effects. Conversely, the rapid elimination of a drug
means that the patient has to receive either increased doses, with a greater risk of
toxic side effects, or more frequent doses, which carries more risk of under- or
over-dosing. The main excretion route for drugs and their metabolites is
through the kidney in solution in the urine. However, a significant number
of drugs and their metabolic products are also excreted via the bowel in the
faeces.
52 AN INTRODUCTION TO DRUGS AND THEIR ACTION