MECHANISM OF PERIPHERALLY VS CENTRALLY ACTING ANALGESICS

Peripherally acting analgesics inhibit the synthesis and/or release of prostaglandins. This is a good way to determine drugs like aspirin and ibuprofen (peripherally acting) from codeine (centrally acting). With severe pain, we want to block central perception. So drugs like morphine and codeine bind to specific receptors in the CNS called opiate receptors, and thus act as agonistic activity on the receptor site.

When we’re talking about central pathways, we’re talking about drugs that effect the transmission of pain from the spinal cord up through the thalamic nuclei, etc. This is to be distinguished from peripheral nerve blocks, from local anesthetics—this is NOT analgesia. Analgesics do not interfere with nerve conduction!!!

Central acting agents modify pain by working on the higher CNS centers by blocking the perception of pain, or they may act on the limbic system to alter the emotional, or interpretation of pain response.

CNS analgesics DO NOT block pain fiber nerve transmission, block peripheral pain receptor(s), or act as local anesthetics.

Pain receptor(s) may be stimulated by touch, heat/cold, pain mediators, prostaglandins, substance P.

Category: Pharmacology Notes