Diclofenac Sodium (Diclomax SR)
Is It Right for You?
A complete guide to Diclofenac Sodium (Diclomax SR) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Diclofenac Sodium (Diclomax SR)?
Diclomax SR is a sustained-release oral formulation of diclofenac sodium — a non-steroidal anti-inflammatory drug (NSAID) — presented in 75 mg capsules. The sustained-release matrix allows once- or twice-daily dosing with more consistent plasma concentrations compared to immediate-release diclofenac preparations, reducing peak-related gastrointestinal exposure while maintaining effective anti-inflammatory and analgesic levels throughout the day.
Diclofenac is a phenylacetic acid derivative NSAID that inhibits both COX-1 and COX-2, reducing the synthesis of prostaglandins mediating inflammation, pain, and fever. It is one of the most widely prescribed NSAIDs globally and is available in numerous formulations including oral tablets, suppositories, topical gels, and eye drops.
Diclomax SR is a prescription-only medication in the UK. A licensed clinician must assess your gastrointestinal, cardiovascular, and renal risk profile before prescribing.
What Conditions Is Diclomax SR Used For?
Diclomax SR is indicated for:
relief of pain and inflammation in degenerative joint disease
symptom management in active disease as part of a broader treatment strategy
management of spinal pain and inflammation
soft tissue injuries, back pain, and post-traumatic inflammation
short-term treatment of acute gouty arthritis attacks
short-term analgesic use following surgery
Diclofenac reduces pain and inflammation but does not slow the progression of rheumatoid arthritis or osteoarthritis. Disease-modifying therapies, weight management, and physiotherapy remain central to long-term disease management.
How Does Diclomax SR Work?
Diclofenac is a non-selective inhibitor of the cyclo-oxygenase (COX) enzyme system, inhibiting both COX-1 and COX-2 isoforms, though it demonstrates preferential activity at COX-2 at therapeutic doses — a property that partly explains its relatively lower GI toxicity compared to some other traditional NSAIDs.
Anti-inflammatory and analgesic effects — inhibition of COX-2 at sites of inflammation reduces the conversion of arachidonic acid to prostaglandins (PGE₂, PGI₂), the key mediators of vasodilation, oedema, and pain receptor sensitisation. This results in reduced inflammation, pain, and swelling.
Antipyretic effect — prostaglandins act in the hypothalamus to raise the thermoregulatory set point. COX inhibition reduces hypothalamic prostaglandin synthesis, lowering fever.
COX-1 inhibition — inhibition of COX-1 in the gastric mucosa reduces the production of cytoprotective prostaglandins, increasing the risk of gastric erosion and ulceration — the principal GI harm of NSAID therapy.
The SR formulation provides a slower, more sustained release of diclofenac, reducing peak plasma concentration fluctuations and GI mucosal exposure compared to immediate-release preparations.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Swallow the SR capsule whole — do not crush, chew, or open it. Breaking the sustained-release matrix will result in rapid drug release and loss of the SR benefit.
Take with or after food to reduce the risk of gastric side effects, even though the SR formulation is designed to reduce GI peak exposure.
Take at consistent times — once or twice daily as prescribed — to maintain stable plasma levels.
Use the lowest effective dose for the shortest duration, particularly in patients with cardiovascular or GI risk factors.
Do not combine with other NSAIDs including over-the-counter ibuprofen or aspirin — additive GI and cardiovascular risk without additional benefit.
Side Effects of Diclomax SR
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Gastrointestinal discomfort — nausea, dyspepsia, abdominal pain, diarrhoea
- Headache
- Dizziness
- Elevated liver enzymes — usually mild and reversible
- Fluid retention / oedema
- Raised blood pressure
- Gastrointestinal ulceration, perforation, or bleeding — black or tarry stools, vomiting blood, severe abdominal pain
- Myocardial infarction or stroke — all NSAIDs carry a small increased cardiovascular risk, particularly with long-term use; chest pain, sudden severe headache, arm weakness, speech disturbance
- Acute kidney injury — particularly in volume-depleted patients or those with pre-existing renal impairment; reduced urine output, leg swelling
- Severe hepatotoxicity — jaundice, dark urine, right upper abdominal pain; rare
- Severe allergic reaction / anaphylaxis
- Serious skin reactions — Stevens-Johnson Syndrome; rare
All non-selective NSAIDs, including diclofenac, increase the risk of serious GI events (ulceration, bleeding) and thrombotic cardiovascular events (MI, stroke) — particularly with long-term use and at higher doses. GI protective therapy with a proton pump inhibitor should be co-prescribed in patients with risk factors. Diclofenac carries a higher cardiovascular risk than naproxen and ibuprofen among traditional NSAIDs, and should be used with particular caution in patients with established or high-risk cardiovascular disease.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Diclomax SR
NSAIDs reduce methotrexate clearance; risk of severe toxicity, particularly at oncological doses.
NSAIDs reduce antihypertensive and diuretic efficacy and increase the risk of acute renal failure, particularly in the elderly or dehydrated.
increased risk of GI bleeding when combined with NSAIDs; consider GI protection.
may reduce absorption of some diclofenac formulations; not clinically significant with the SR preparation.
Important Warnings
Diclofenac is associated with a higher risk of cardiovascular thrombotic events than some other NSAIDs and should be avoided or used with extreme caution in patients with established cardiovascular disease, recent MI, or stroke.
NSAIDs significantly increase the risk of GI ulceration, perforation, and bleeding. A proton pump inhibitor should be co-prescribed in all patients with risk factors including age over 65, prior GI history, or concurrent aspirin or corticosteroid use.
Diclofenac is contraindicated in severe renal impairment (eGFR <30 mL/min). It should be used with caution in patients with reduced renal reserve, heart failure, or liver disease.
Diclofenac has been associated with serious hepatic events more frequently than other NSAIDs. Liver function should be monitored during prolonged treatment.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Diclomax SR FAQs
The SR formulation releases diclofenac slowly, maintaining more consistent blood levels throughout the day. This reduces the GI peak-dose exposure associated with immediate-release tablets and allows for more convenient once or twice daily dosing.
Long-term NSAID use carries risks of GI damage, cardiovascular events, and renal impairment. Prolonged use should only occur under regular clinical review, with GI protection (PPI) co-prescribed, and at the lowest effective dose.
Yes — paracetamol and diclofenac work through different mechanisms and can be safely combined, often with additive analgesic benefit.
Clinical evidence and regulatory reviews have consistently shown that diclofenac, particularly at higher doses, is associated with a greater increase in cardiovascular thrombotic events (MI, stroke) compared to naproxen and low-to-moderate dose ibuprofen. It is therefore contraindicated in patients with established cardiovascular disease.
Your clinician will assess your GI risk. For many patients — particularly those over 65, or with a history of peptic ulcer disease or concurrent aspirin use — co-prescribing a PPI (such as omeprazole or lansoprazole) is recommended.