Analgesics

Question 0

What is paracetamol used for?

Answer 0

Most frequently used as analgesic for mild to moderate pain. Also used in pyrexia to decrease body temperature.

Does not have anti-inflammatory action

Mechanism still not fully understood - now believes to stimulate cannabinoid receptors.

Few side effects and safe in elderly but toxic to liver cells if normal dose exceeded.

Adult dose 1gram every 4-6 hrs with maximum of 4 grams in 24 hrs

Question 1

What is the analgesic ladder? Name a few drugs for each rug.

Answer 1

Essentially 3 steps :

1. Non-opioids e.g paracetamol, NSAIDs, e.g ibuprofen - ceiling doses limit the effect.
2. Mild opioids e.g. Codeine, dihydrocodeine. May be combined with paracetamol or a NSAID.
3. Strong opioids - e.g. Morphine. Later doses give greater relief with no ceiling effect.

Question 2

NSAIDS : give examples

Answer 2

Aspirin, ibuprofen, naproxen, fenbufen, diclofenac, piroxicam

Question 3

NSAIDS: used for and side effects …

Answer 3

Very useful in chronic inflammatory conditions.

Pain relief is immediate but full anti inflammatory action takes up to three weeks.

Side effects of gastric and peptic ulcers formulation due to thinning of the mucosal lining in the gut. Frequently present in haematemesis, especially in the elderly.
Newer selective cox-2 inhibitors do not have the gastric side effects but increase incidences of myocardial infarction so not used in high risk of CVD.
Aspirin used in small dose (75 micrograms daily) as anti platelet drug in CVD prevention.

NSAIDs should jot be given to asthmatics as some are aspirin sensitive.

All work by inhibiting the enzyme cyclo-oxygenase(CIC) needed for the synthesis of prostaglandins.

Question 4

Opioids : uses, side effects and mechanism …

Answer 4

Used to relieve moderate to severe pain, especially if visceral.

Powerful analgesic and changes the perception of pain. Tolerance and dependable may occur with repeated administration.

Most used is morphine derived from the opium poppy. Also produces euphoria and a sense of detachment from surroundings.

All are agonists at the opioid receptors in the CNS. One major side effect is in large doses is respiratory depression. Other side effects include nausea, vomiting, constipation and drowsiness.

Pinpoint pupils sign opioids taken.

Antidote is naloxone - opioid antagonist. Has shorter life than morphine so in cases if overdose needs to be given repeatedly or as continuous infusion.

Question 5

Common opioids..

Answer 5

Morphine - standard opioid powerful analgesic.

Diamorphine - powerful. Enters brain readily. Popular with addicts. Used in palliative care.

Fentanyl, alfentanil, remifentanil - very potent. Used during operations as analgesic. Fentanyl also available in patches and lozenges. Used in palliative care.

Meotazinol - claimed to have less redo depressant action.

Methadone - long acting and less sedating. Also used to wean off heroin.

Oxycidone - controls pain in palliative care.

Pethidine - less constipating but less potent.

Tramadol - use for moderate to severe pain. Also acts on serotonin and adrenaline pathways. Less constipating and resp. depressing.

Codeine - too constipating for long term use but effective for moderate pain.

Dihydrocodeine - similar to codeine in analgesic effect.

Bupernorphine - agonist and antagonist at opioid receptors. Only partially reversed by naloxone. Longer acting than morphing and available sublingual my ( acts 6-8hrs) can produce withdrawal symptoms in addicts. Is dependency producing itself.