Diclofenac
Class: non-steroidal anti-inflammatory drug (NSAID)
Indications (NB some may be unlicensed): pain associated with inflammation, itch, sweating (neoplastic fever)
Contraindications/cautions: Hypersensitivity to aspirin or other NSAIDs, GI ulceration, asthma (in sensitive patients), renal, cardiac or hepatic impairment, bleeding or other bleeding disorders
Adverse reactions: common: GI ulceration (more common if elderly, on steroids or aspirin), diarrhoea, indigestion, nausea; less common: dizziness, rash, nephrotoxicity, hepatitis, oedema, hypertension, headache, tinnitus, proctitis (rectal administration)
NB inhibits platelet aggregation – may prolong bleeding time. Caution if concurrent prescription with warfarin (PCF) – monitor INR
Metabolism/clearance: metabolised by metabolising enzyme CYP2C9 mainly in the liver
Interactions:
- increased clinical effect/toxicity of diclofenac (due to increased blood concentrations) may occur with some CYP metabolising enzyme inhibitors (see above) e.g. fluconazole
- decreased clinical effect/toxicity of diclofenac (due to decreased blood concentrations) may occur with some CYP metabolism enzyme inducers (see above) e.g. phenobarbitone, phenytoin, rifampicin
- increased risk of renal toxicity and hyperkalaemia with ACE inhibitors (e.g. enalapril)
- increased risk of gastro-intestinal bleed with corticosteroids (e.g. dexamethasone)
- increased clinical effect/toxicity of lithium, digoxin, methotrexate, warfarin may occur with concomitant diclofenac so monitor
- decreased clinical effects of diuretics (e.g. furosemide), antihypertensives (e.g. propranolol) may occur with concomitant diclofenac
| Dosing: | |
|---|---|
| oral: | 50 to 150 mg per day in 3 divided doses for normal release and 2 divided doses (sometimes just one) for long acting preparations |
| subcut: | inj available but not for subcut injection as too irritant |
| rectal: | as for normal release oral |
Syringe driver: not recommended
Mechanism of action: inhibits prostaglandin synthesis – resulting in analgesic, anti-inflammatory and anti-pyretic action
Peak effect: oral (normal release): 0.3 to 2 hours
Duration: oral (normal release): 6 to 8 hours
Notes:
- co-analgesic often used with opioids in bone and soft tissue pain
- NSAID of choice in palliative care
- patients at risk of gastro-intestinal bleeds should be prescribed gastric protection (e.g. pantoprazole, omeprazole) prophylactically