Re: how do pain killers, such as paracetamol, work?

Dear Heather,
I apologize for taking so long to answer your question.

Many pain relieving drugs, such as paracetamol (also called 
acetaminophen), act to inhibit the synthesis of a group of chemicals 
called prostaglandins.  These drugs inhibit a group of enzyme termed 
cyclooxygenases.  A recent report (Chandrasekharan et al. 2002) 
demonstrates that paracetamol inhibits an enzyme called cyclooxygenase 3 
(COX-3).  COX-3 is also inhibited by phenacetin, another analgesic. 
 
Other members of the cyclooxygenase family include COX-1 and COX-2, which 
are inhibited by aspirin and several nonsteroidal anti-inflammatory drugs 
(see the discussion at this web site:
 http://webcampus.med.drexel.edu/cme/medicine/nsaids/mechanisms.htm).

COX-2 inhibitors have received much attention recently because they 
relieve pain and inflammation without causing the severe gastrointestinal 
distress (such as ulcers) that results from non-selective COX inhibitors.  
Thus, they are prescribed for treating chronic pain.



Chandrasekharan et al (2002) COX-3, a cyclooxygenase-1 variant inhibited 
by acetaminophen and other analgesic/antipyretic drugs: cloning, 
structure, and expression.  Proc Natl Acad Sci USA 99(21):13926-31.