Thiol drug substances

Representative thiol drug substances that are susceptible to oxidation. 

Oxidation mechanisms for drug substances depend on the chemical structure of the drug and the presence of reactive oxygen species or other oxidants. Catechols such as methyl-dopa180 and epinephrine181 are readily oxidized to quinones, as shown in Scheme 45. 5-Aminosalicylic acid undergoes oxidation and forms quinoneimine,182 which is further degraded to polymeric compounds (Scheme 46).183 Ethanolamines such as procaterol are oxidized to formyl compounds (Scheme 47),184 whereas thiols such as 6-mercaptopurine,185... 

Barbiturates and alcohol both increase the activity of (induce) the enzymes that metabolize paracetamol to the toxic product. A chronic alcohohc or someone who has been prescribed barbiturate drugs will be at greater risk when taking more than the recommended dose of paracetamol because a greater proportion of the dose will be converted into the toxic product. It would be equivalent to taking a larger dose. In the case of an alcoholic the liver may already be compromised by repeated and long-term alcohol abuse and so be more vulnerable and less able to detoxify paracetamol it may also have less protective substances like thiols. 

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