CNS Flashcards
(134 cards)
What are central analgesics?
drugs which relieve pain by central action without impairing consciousness or other sensations
What are central analgesics classified into?
- non-steroidal anti-inflammatory drugs (NSAIDs) = analgesic antipyretic drugs
- opioid (narcotic) analgesic drugs
What do NSAIDs do?
- relieve low intensity pain (e.g. headache, neuralgia, myalgia)
- act subcortical on thalamus
- no euphoria or drowsiness
- non addictive
- no tolerance
What do opioids do?
- relieve any type of pain (except itching)
- cortical and subcortical
- produce euphoria and addiction
What are peripheral analgesics?
include physical protectives, local and surface anaesthetics, obtundents, astringents and counter-irritants
What is the function of NSAIDs?
inhibit COX (cyclo-oxygenase) enzyme which inhibits prostaglandin (PG) synthesis
What are the types of COX enzymes and their function?
- COX 1: mainly constitutive (present normally in tissue regulation in physiologic functions), responsible for forming protective PGs in GIT and kidney
- COX 2: inducible in inflammation, constitutive in endothelium and kidney
- COX 3: newly discovered and under investigation, mainly CNS
What are some characteristics of PGs?
- made in cells in body normally
- stimulate nerve impulse and pain sensation
- induce fever
- not an enzyme or hormone
- found all around the body
What breaks down phospholipids?
phospholipase A2
What is the product of phospholipid breakdown by phospholipase A2
- fatty acids (mainly arachidonic acid)
- glycerol
How is prostaglandin secreted by arachidonic acid?
- by COX enzyme (90%)
- by lipoxygenase (LOX) enzyme which releases leukotrienes (10%)
What happens if there is excessive leukotrienes present in the lungs?
bronchospasm which develops to bronchial asthma
What is the function of leukotrienes?
- inflammatory mediator
- has a function in the immune system
What are the general functions of PGs?
- induce pain, fever and inflammation
- contract uterus (during labour and pregnancy)
- prevent peptic ulcer (protects stomach lining)
- maintain patency of ductus arteriosus in the foetus
- increase renal blood flow
- thromboxane A2 (released from platelets) produces VC and increase platelet aggregation during injury
- prostacyclin produces VD and reduces platelet aggregation
What are the therapeutic uses and side effects of aspirin-like drugs (NSAIDs)?
- analgesic, antipyretic and anti-inflammatory (paracetamol has no anti-inflammatory action)
- can be used in dysmenorrhea (pain during menstruation), patent ductus arteriosus and tocolytic (relax uterus) in premature labour
- affect platelet function and can be used as antithrombotic (decrease thrombosis and thromboxane A2)
- can induce gastric or intestinal ulcerations
- may induce bronchospasm and urticaria in susceptible patients due to increase in leukotrienes (product of LOX pathway)
- have little effect on renal function in normal subjects but may decrease renal blood flow and glomerular filtrate in renal diseases and could lead to neuropathy (they produce salt and water retention)
- use of aspirin-like drugs in pregnant women is not recommended but if there is need, aspirin is te safest anti-inflammatory while paracetamol is the safest analgesic antipyretic
- most of the NSAIDs bind firmly to plasma proteins and can displace other drugs as warfarin, oral hypoglycaemics, inducing serious drug interactions
Why does paracetamol have no anti-inflammatory effects?
because it inhibits COX 3 enzyme only which works centrally
What does antipyretic mean?
decrease temperature to normal
What is the classification of analgesic antipyretic drugs?
- non-selective COX inhibitors
- selective COX 2 inhibitors
- selective COX 3 inhibitors
What are examples of non-selective COX inhibitors?
- salicylates (aspirin)
- indomethacin
- ibuprofen
- ketoprofen
- diclofenac
- piroxicam
What is a selective COX 2 inhibitor example?
celecoxib
What is a selective COX 3 inhibitor example?
paracetamol
What are the characteristics of salicylates?
- derived from salicylic acid which is highly irritant
- example is aspirin
What are the pharmacokinetics of non-selective COX inhibitors?
- effective orally
- complete absorption in upper part of small intestine
- excreted in urine
- alkaline urine increases excretion by sodium bicarbonate
What are the local actions of non-selective COX inhibitors?
- salicylic acid: keratolytic (remove dead cells), antifungal and antiseptic
- -methyl salicylate (oil of winter green): counter-irritant