Diclofenac (marketed as Voltaren, Voltarol, Diclon 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. Diclofenac is available in stomach acid resistant formulations (25 and 50 mg), fast disintegrating oral formulations (50 mg), slow- and controlled-release forms (75, 100 or 150 mg), suppositories (50 and 100 mg), and injectable forms (50 and 75 mg). Diclofenac is also available over the counter (OTC) in some countries: Voltaren dolo (12.5 mg diclofenac as potassium salt) in Switzerland and Germany, and preparations with 25 mg diclofenac are OTC in New Zealand. OTC use is approved for minor aches and pains and fever associated with common infections.
Diclofenac is available as a generic drug in a number of formulations.
Mechanism of action
The exact mechanism of action is not entirely known, but it is thought that the primary mechanism responsible for its anti-inflammatory/antipyretic/analgesic action is 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. Diclofenac has a low to moderate preference to block the COX2-isoenzyme (approximately 10-fold) and is said to have therefore a somewhat lower incidence of gastrointestinal complaints than noted with indomethacin and aspirin.
The action of one single dose is much longer (6 to 8 hours) than the very short half-life of the drug indicates. This could partly be due to a particular high concentration achieved in synovial fluids.
Diclofenac is used for musculoskeletal complaints, especially arthritis (rheumatoid arthritis, osteoarthritis, spondylarthritis, ankylosing spondylitis), gout attacks, and pain management in case of kidney stones and gallstones. An additional indication is the treatment of acute migraines. Diclofenac is used commonly to treat mild to moderate post-operative or post-traumatic pain, particular when inflammation is also present, and is effective against menstrual pain.
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.
An external, gel-based form of diclofenac (Solareze) is available for the treatment of facial actinic keratosis which is caused by over-exposure to sunlight. Some countries have also approved the external use of diclofenac gel to treat muskoskeletal conditions.
Over-the-counter use against minor aches and pains and fever associated with common infections is also licensed in some countries.
In many countries eye-drops are sold to treat acute and chronic non-bacterial inflammations of the anterior part of the eyes (e.g. postoperative states). A common brand name is Voltaren-ophta.
Off label/investigational uses
Diclofenac is often used to treat chronic pain associated with cancer, particular if inflammation is also present (Step I of the World Health Organisation (WHO) Scheme for treatment of chronic pain). Good results (sometimes better than those with opioids) have been seen in female breast cancer and in the pain associated with bony metastases. Diclofenac can be combined with opioids if needed. In Europe Combaren exists, a fixed combination of diclofenac and codeine (50 mg each) for cancer treatment. Combinations with psychoactive drugs such as chlorprothixene and/or amitriptyline have also been investigated and found useful in a number of cancer patients.
Fever due to malignant lymphogranulomatosis (Hodgkin's lymphoma) often reponds to diclofenac. Treatment can be terminated as soon as the usual treatment with radiation and/or chemotherapy causes remission of fever.
Diclofenac may prevent the development of Alzheimer's disease if given daily in small doses during many years. All investigations were stopped after it was found that some of the other investigated NSAIDs (naproxen, rofecoxib) caused a higher incidence of death cases due to cardiovascular events and stroke compared to placebo.
Diclofenac has been found to increase the blood pressure in patients withs Shy-Drager syndrome (autonomous hypotension) often seen in diabetic patients. Currently, this use is highly investigational and cannot be recommended as routine treatment.
Hypersensitivity against diclofenac
History of allergic reactions (bronchospasm, shock, rhinitis, urticaria) following the use of Aspirin or another NSAID
Active stomach and/or duodenal ulceration or gastrointestinal bleeding
Inflammative intestinal disorders such as Crohn's disease or ulcerative colitis
Severe insufficiency of the heart (NYHA III/IV)
Recently, a warning has been issued by FDA not to treat patients recovering from heart surgery
Severe liver insufficiency (Child-Pugh Class C)
Severe renal insufficiency (creatinine clearance <30 ml/min)
Caution in patients with preexisting hepatic porphyria, as diclofenac may trigger attacks
Caution in patients with severe, active bleeding such as cerebral hemorrhage
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 gastrointestintal complaints.
Gastrointestinal complaints are most often noted (see above). The development of ulceration and/or bleeding requires immediate termination of treatment with diclofenac. Most patients receive an ulcer-protective drug as prophylaxis during longterm treatment (misoprostol, ranitidine 150mg at bedtime or omeprazole 20 mg at bedtime).
Liver and renal damage occur infrequently, but are usually reversible. Hepatitis may occur rarely without any warning symptoms and may be fatal. Patients with osteoarthritis develop more often symptomatic liver disease than patients with rheumatoid arthritis. Liver and kidney function should be monitored regularly during longterm treatment. If used for the shortterm treatment of pain or fever, diclofenac has not been found to be more hepatotoxic than other NSAIDs.
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.
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.
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