Voltaren (diclofenac) is among the better tolerated NSAIDs

Diclofenac (Voltaren) is a non-steroidal anti-inflammatory drug (NSAID) taken to reduce inflammation and as an analgesic reducing pain in conditions such as arthritis or acute injury. It can also be used to reduce menstrual pain and dysmenorrhea.

Diclofenac is among the better tolerated NSAIDs. Though 20% of patients on long-term treatment experience side effects, only 2% have to discontinue the drug, mostly due to gastrointestinal complaints.

Cardiac side effects

Following the identification of increased risks of heart attacks with the selective COX-2 inhibitor rofecoxib in 2004, attention has focused on all the other members of the NSAIDs group, including diclofenac. Research results are mixed with a meta-analysis of papers and reports up to April 2006 suggesting a relative increased rate of heart disease of 1.63 compared to non users. Professor Peter Weissberg, Medical Director of the British Heart Foundation said, "However, the increased risk is small and many patients with chronic debilitating pain may well feel that this small risk is worth taking to relieve their symptoms". Only Aspirin was found not to increase the risk of heart disease, however this is known to have a higher rate of gastric ulceration than diclofenac. A subsequent large study of 74,838 users of NSAIDs or coxibs, published in May 2006 found no additional cardiovascular risk from diclofenac use.

Diclofenac has similar COX-2 selectivity to celecoxib. Perhaps related to this selectivity, it was concluded, that diclofenac does increase the risk of myocardial infarction.

Gastrointestinal side effects

Gastrointestinal complaints are most often noted. The development of ulceration and/or bleeding requires immediate termination of treatment with diclofenac. Most patients receive an ulcer-protective drug as prophylaxis during long-term treatment (misoprostol, ranitidine 150 mg at bedtime or omeprazole 20 mg at bedtime).

Hepatic side effects

Liver damage occurs infrequently, and is usually reversible. Hepatitis may occur rarely without any warning symptoms and may be fatal. Patients with osteoarthritis more often develop symptomatic liver disease than patients with rheumatoid arthritis. Liver function should be monitored regularly during long-term treatment. If used for the short term treatment of pain or fever, diclofenac has not been found to be more hepatotoxic than other NSAIDs.

Renal side effects

Studies in Pakistan showed that diclofenac caused acute kidney failure in vultures when they ate the carcasses of animals that had recently been treated with it. Species and individual humans that are drug sensitive are initially assumed to lack genes expressing specific drug detoxification enzymes.

NSAIDs "are associated with adverse renal (kidney) effects caused by the reduction in synthesis of renal prostaglandins" in sensitive persons or animal species, and potentially during long term use in non-sensitive persons if resistance to side effects decreases with age. Unfortunately this side effect can't be avoided merely by using a COX-2 selective inhibitor because, "Both isoforms of COX, COX-1 and COX-2, are expressed in the kidney. Consequently, the same precautions regarding renal risk that are followed for nonselective NSAIDs should be used when selective COX-2 inhibitors are administered." However, diclofenac appears to have a different mechanism of renal toxicity.

Other side effects

Bone marrow depression is noted infrequently (leukopenia, agranulocytosis, thrombopenia with/without purpura, aplastic anemia). These conditions may be life-threatening and/or irreversible, if detected too late. All patients should be monitored closely. Diclofenac is a weak and reversible inhibitor of thrombocytic aggregation needed for normal coagulation.

Diclofenac may disrupt the normal menstrual cycle.