Analgesia

Prescribing involves balancing benefit vs harm and paracetamol causes very little harm with proven benefit. This creates a very low threshold to recommend paracetamol. It  has been found to work in conjunction with opiates and reduces opioid requirement. Therefore for mild pain paracetamol is first line in the hope that it can be sufficiently managed.

In severe pain it is reasonable to prescribe nsaids, opioids or something else and in this case regular paracetamol should be given regularly.  Anecdotally paracetamol produces a small but significant benefit. 

Dosing: 1g QDS if >50kg, 500mg QDS if < 50kg.

A caution to note is its metabolism in the liver. The common clinical question is analgesia for acute cholecystitis and when can paracetamol be given.  I believe the rule is if the ALT/AST are normal then paracetamol can be given. Paracetamol can be given in pregnancy and AKI. Another caution are medication headaches and paracetamol should be used as required whilst the headache is present. Regular paracetamol has been found to cause medication headaches. 

NSAIDs are COX inhibitors,, with most NSAIDs inhibiting both COX-1 and COX-2. Inhibiting COX-2 produces the analgesic effect however COX-1 causes gastrointestinal bleeding. Selective COX-2 inhibitors were developed with the hope that these would have the same analgesic efficacy with fewer side effects, however they were found to have increased cardiovascular events. Therefore selective COX-2 inhibitors are rarely used. Celecoxib is an example. 

NSAIDs tend to be incredibly effective analgesics and are a personal favourite to prescribe, though be wary of the GI and kidney side effects in the elderly. Paracetamol should be co-prescribed.

NSAID types

1. Ibuprofen 200-400mg TDS

2. Naproxen 500mg BD

3. Diclofenac 75mg BD (PR)

Ibuprofen is the commonly prescribed nsaid. I have been told that 200mg has the same efficacy as 400mg with fewer side effects but I would say this is not widely accepted. 

Naproxen tends to be given for more severe pain, requiring long acting NSAIDs. Naproxen is a strong analgesia however comes with significant NSAID side effects to the kidneys and GI tract. 

PR diclofenac is given for kidney stones because it is absorbed quickly and incredibly effective at relieving a severe pain in usually an healthy individual. 

Cautions

Typically NSAIDs cause worsening of kidney function and GI bleeds. This is particularly significant in the elderly and those over 65 years should have PPI protection (omeprazole) for regular courses of NSAIDs and should take these long term. Topical formulations are good for example knee osteoarthritis in delivering pain relief in the elderly without causing side effects. 

Conversions

Conversion factor

8mg  PO morphine = 80mg PO codeine 10

8mg PO morphine = 4mg sc morphine 1/2

Renal excretion

Accumulation of morphine-6-glucoronide can cause opioid toxicity

Every categorisation system should have an 'everything else' box. This one cont