Paracetamol, Metamizole and others:
Nobody knows precisely where paracetamol, dipyrone or nefopam
work. The standard explanation for paracetamol is that it acts as
a Cox inhibitor in the brain, explaining both its analgesic and its
antipyretic actions. The lack of clinical anti-inflammatory activity
may be because paracetamol is not active on peripheral Cox. Similar
comments are made for dipyrone. Nefopam, while undoubtedly an analgesic, has neither opioid nor NSAID-like activity. It is neither anti-inflammatory nor antipyretic, and, like paracetamol and dipyrone, its site of action is presumed to be in the central nervous system.
Analgesic and antipyretic: WEAK ANTI-INFLAMMATORY ACTION … ASA. Also does not
produce gastric irritation and prolonged bleeding times characteristic of salicylates.
Not clear why pharmacology is different from ASA. Two common explanations:(1) only blocks
cyclo-oxygenases in environment low in peroxides and [peroxide] is high in area of inflammation,
(2) selectively inhibits a CNS isozyme of cyclo-oxygenase.