Diclofenac

Diclofenac (marketed as Voltaren®, Voltarol® and Cataflam®) is a non-steroidal anti-inflammatory drug (NSAID) taken to reduce inflammation, such as in arthritis or acute injury. It can also be used to reduce menstrual pain. Voltaren and Voltarol contain the sodium salt of diclofenac. In the United Kingdom Voltarol can be supplied with either the sodium salt or Potassium salt, while Cataflam in some other countries, is the potassium salt only.

Mechanism of action

The exact mechanism of action is not entirely known, but it is thought that the primary action responsible for its anti-inflammatory/antipyretic/analgesic action is through inhibition of prostaglandin synthesis by inhibition of cyclooxygenase (COX).

Diclofenac, it seems, may also be a unique member of the NSAIDs. There is some evidence that diclofenac inhibits the lipooxygenase pathways, thus reducing formation of the leukotrienes (also pro-inflammatory autacoids). There is also speculation that diclofenac may inhibit phospholipase A₂ as part of its mechanism of action. These additional actions may explain the high potency of diclofenac - it is the most potent NSAID on a molar basis.

Inhibition of COX also decreases prostaglandins in the epithelium of the stomach, making it more sensitive to corrosion by gastric acid. This is also the main side effect of diclofenac and other drugs that are not selective for the COX2-isoenzyme.

Uses

Diclofenac is used for musculoskeletal complaints, especially arthritis (rheumatoid arthritis and osteoarthritis), and pain management in case of kidney stones.

As long-term use of diclofenac and similar NSAIDs predisposes for peptic ulcer, many patients at risk for this complication are prescribed a combination (Arthrotec) of diclofenac and misoprostol, a synthetic prostaglandin analogue, to protect the gastric mucosa.

Environmental problems

Use of diclofenac in animals has been reported¹ to have led to a sharp decline in the vulture population in the Indian subcontinent, up to 95% in some areas. The mechanism is probably renal failure, a known side-effect of diclofenac. Vultures eat the carcasses of animals that have been administered diclofenac, and are poisoned by the accumulated chemical.

Reference

• Note 1: Oaks JL, Gilbert M, Virani MZ, Watson RT, Meteyer CU, Rideout BA, Shivaprasad HL, Ahmed S, Chaudhry MJ, Arshad M, Mahmood S, Ali A, Khan AA. Diclofenac residues as the cause of vulture population decline in Pakistan. Nature 2004;427:630-3. PMID 14745453.