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Pain-Killers 

WHO pain ladder

Adjuvants: anticonvulsants (neuropathic), TCAs
  1. Non-opioid (aspirin, paracetamol, NSAID) ± adjuvant
  2. Opioid for mild/moderate pain (Co-codamo) ± Non-opioid ± Adjuvant
  3. Opioid for moderate/severe pain (morphine, diamorphine, fentanyl, oxycodone, hydromorphone) ± Non-opioid ± Adjuvant. Oral morphine is drug of choice.

Morphine

Morphine is available in liquid, tablet, normal and controlled release preparations. Oral morphine should be given every 4 hours.
Titrating morphine: Starting dose is 2.5-10mg 4 hourly (reduce in elderly or impaired renal function).
Breakthrough pain: Pain which occurs between regular doses: give a dose equivalent to the 4 hourly dose. Normal regime continued even if breakthrough dose taken. After 24 hours the new dose of morphine is the net morphine in that time divided by 6 (if given 6 times a day), and the rescue doses increased accordingly.
Maintenance : Once dose titrated, patient may prefer convenience of controlled release perparation of morphine. The 12 hourly controlled release (MST Slow Release, tradename zomorph) is the 24 hour dose divided by 2.
Adverse Effects: Nausea/vomiting, hallucinations, itching, tolerance/dependence (rare if true pain)
Nausea: Give morphine with an anti-emetic e.g. cyclizine 50mg PO/IV/IM TDS. Maximum 150mg in 24h.

Oxycodone

At higher doses morphine has poor solubility & oxycodone is preferred. 
Dose: Divide morphine dose by 3

Codeine Phosphate

Uses: Mild to moderate pain, diarrhoea
Dose: Oral 30-60mg every 4h
Adverse Effects/Contraindications: see morphine

Co-codamol x/Y

Co-codamol is combination of codeine/paracetamol, where x is mg of codeine phosphate, and y is mg of paracetamol.
Dose: Often 30/500 for moderate pain

NSAIDs

Mechanism: Pain relief, anti-inflammatory

Examples

Diclofenac: Pain/inflammation in rheumatoid arthritis, acute gout, post-op
Ibuprofen: “”, fever/pain in children, dysmenorrhoea, migraine. 1.2-1,8g daily in divided doses

Adverse Effects

GI discomfort/bleeding (should take with meals), hypersensitivity, renal failure
Contraindications: Asthma, hypersensitivity to any NSAID, severe heart failure. COX2s are CI in some CVS diseases now. NSAIDs may interfere with renal function, fluid retention.

Aspirin

Mechanism: COX inhibitor, an NSAID. Aniplatelet: stops aggregation of platelets.

Uses

Pain relief: 300-900mg every 4-6 h, max 4g daily. Alternative: paracetamol
CVS disease as an antiplatelet: 75mg daily. Alternative: clopidogrel

Adverse Effects

GI bleeding/irritation (so take after food), bronchospasm
Contraindications: Reyes's syndrome, Children < 16y, breast feeding, Hypersensitivity, Previous reaction to an NSAID e.g. asthma/angiodema

Paracetamol

Mechanism: COX inhibition. It is not an NSAID: does not irritate the lining of the stomach, affect blood coagulation as much as NSAIDs, or affect function of the kidneys.
Uses: Mild to moderate pain, pyrexia
Dose: 0.5-1g every 4-6h to a max 4g daily. Can also be given (rarely) as IV infusion, rectal
Adverse Effects: Liver damage in overdose. Rashes, blood disorders (e.g. thrombocytopenia).
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