All of the following drugs are metabolized by acetylation except: (DNB June 2012)
Drugs metabolized by Acetylation:
All the drugs having amino or hydrazine residues e.g :
- INH (Isoniazid)
N-acetyl transferase is a key enzyme in phase-II reaction and is most common enzyme that mediates acetylation. There are two kinds of acetylators: slow and fast. Majority of people are slow acetylators (including Indians) and fast acetylators (western patients). Peripherals neuropathy is more common in slow acetylators while hepatitis is more common in fast acetylators.
Synthetic / Phase – II biotransformation reactions:
All compounds having hydroxyl or carboxylic acid groups
- Chloramphenicol - Aspirin
- Phenacetin - Morphine
- Metronidazole - Endogenous substrates
- Bilirubin - Thyroxine
- Steroid hormones
- Salicylates - Other drugs having carboxylic acid group
It inactivates highly reactive quinone or epoxide intermediates formed during metabolism of certain drugs. e.g.
Amines and phenols are methylated e.g.
- Adrenaline - Histamine - Nicotinic acid
Phenolic compounds and steroids are sulphated e.g.
- Chloramphenicol - Adrenal and sex steroids