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Oral analgesics is the largest OTC medicines category in the UK, with around 80 proprietary products, containing constituents from several therapeutic groups. In this first article in a new series, Alan Nathan discusses NSAIDs. Next month’s article will deal with medicines containing paracetamol and additional constituents

What’s available

The non-steroidal anti- inflammatory drugs available over the counter are: aspirin, diclofenac, ibuprofen and naproxen.

How do they act?

They block the enzyme cyclo-oxygenase, which prevents the formation of prostaglandins – major contributors to inflammation and pain – from arachidonic acid, produced when tissue is damaged. The drugs act locally at the site of inflammation.

What are they licensed for?

Treatment of mild and moderate pain from a wide variety of causes, including headache (specific OTC medicines for migraine are not covered in this article), dental and musculoskeletal pain and dysmenorrhoea. They also have antipyretic action and are used in cold and flu medicines. Naproxen is licensed for OTC sale solely for the treatment of dysmenorrhoea.

Cautions

• Aspirin, diclofenac, ibuprofen and naproxen have similar side-effects. These are generally least pronounced with ibuprofen and most pronounced with aspirin.
• Most common side-effects are gastric irritation and bleeding, so NSAIDs should be avoided by patients with ulcers or a history of gastric problems. Minor gastric side-effects can be reduced by taking the medicines with or after food.
• Hypersensitivity reactions to aspirin are relatively common in patients with asthma or allergic problems: one in 10 patients with asthma may be hypersensitive and suffer severe bronchospasm. Other reactions include urticaria, angioedema and rhinitis. Incidence of hypersensitivity to ibuprofen, diclofenac and naproxen is much lower, but they should be avoided by patients with asthma and individuals sensitive to aspirin, unless they have taken these drugs before without problems.

*NSAIDs should be used with caution in elderly patients, as renal function tends to decline with age and also because the elderly tend to be more vulnerable to gastric side-effects.

Contraindications

• NSAIDs should not be recommended to patients with renal, cardiac or hepatic disease, as they may impair both liver and kidney function.
• They should be avoided during pregnancy.
• Aspirin, but not diclofenac, ibuprofen or naproxen, has been associated with Reye’s syndrome – a rare but potentially fatal brain condition in infants and children. Aspirin is not licensed for use in children under 16 years and should be avoided by breastfeeding women.
• Diclofenac is not licensed for sale for use in children under 14 years. Naproxen is licensed only for females aged 15 to 50 years.

Interactions

• Aspirin potentiates the anticoagulant effect of warfarin and other coumarins because of its inhibitory effect on platelet aggregation and inhibition of vitamin K synthesis. Ibuprofen, diclofenac and naproxen may also enhance the effect of anticoagulants. Patients on anticoagulant therapy should avoid all these drugs.
• Aspirin and, to a lesser extent, ibuprofen, diclofenac and naproxen reduce excretion of methotrexate, potentially causing life-threatening rises in serum levels. Concurrent administration should therefore be avoided.
• OTC NSAIDs may also antagonise the diuretic and antihypertensive effects of diuretics, and should not be recommended to patients taking these drugs.

OTC dosages

Maximum OTC adult doses/day:

• Aspirin – 3,900mg
• Diclofenac – 75mg
• Ibuprofen – 1,200mg
• Naproxen – 750mg

Ibuprofen can be used for babies and children from the age of three months.

How effective are OTC NSAIDS?

• Reports from several clinical trials, systematic reviews and meta-analyses indicate that all OTC analgesic compounds, including paracetamol, are effective and more or less equivalent in the treatment of mild to moderate pain, including headache.
• NSAIDs appear to be more effective than paracetamol for dental pain and dysmenorrhoea.
• There is moderate evidence that NSAIDs are no more effective than paracetamol for acute low-back pain, and paracetamol has fewer side effects.
• Paracetamol and ibuprofen are both safe and effective analgesics and antipyretics for use in children. Ibuprofen appears to have a longer duration of action and to be a more effective antipyretic.

References available on request