The name "diclofenac" derives from its chemical name: 2-(2,6-dichloranilino) phenylacetic acid. Diclofenac was originally developed by Ciba-Geigy (now Novartis) in 1973. It was first introduced in the UK in 1979.
In the United Kingdom, United States, India, and Brazil diclofenac may be supplied as either the sodium or potassiumsalt; in China, it is most often supplied as the sodium salt, while in some other countries it is only available as the potassium salt. Diclofenac is available as a generic drug in a number of formulations, including diclofenac diethylamine, which is applied topically. Over-the-counter (OTC) use is approved in some countries for minor aches and pains and fever associated with common infections.
As long-term use of diclofenac and similar NSAIDs predisposes for peptic ulcer, many patients at risk for this complication are prescribed Arthrotec - a combination of diclofenac and misoprostol, a synthetic prostaglandin (PGE1) analogue, to protect the gastric mucosa.
Diclofenac is also available in topical forms under the brand names Iodex UltraGel, Flector, Pennsaid, Solaraze, and Voltaren for the treatment of conditions such as osteoarthritis, actinic keratosis, and acute pain caused by minor strains, sprains, and contusions (bruises).
In many countries, eye drops are sold to treat acute and chronic nonbacterial inflammations of the anterior part of the eyes (e.g., postoperative states). A common brand name is Voltaren-ophtha.
Diclofenac is often used to treat chronic pain associated with cancer, in particular if inflammation is also present (Step I of the World Health Organization (WHO) scheme for treatment of chronic pain).
Dyloject (diclofenac) 2 ml for IV and IM administration
Diclofenac can be combined with opioids if needed. Under trade names such as Combaren and Voltaren Plus, a fixed combination of diclofenac and codeine (50 mg each) is available in Europe. 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 responds to diclofenac. Treatment can be terminated as soon as the usual treatment with radiation and/or chemotherapy causes remission of fever.
Diclofenac has been found effective against all strains of multidrug-resistant E. coli, with a MIC of 25 micrograms/ml. Therefore, it may have the capacity to treat uncomplicated urinary tract infections caused by E. coli. It has also shown effectiveness in treating Salmonella infections in mice, and is under investigation for the treatment of tuberculosis.
Diclofenac is an antiuricosuric (drugs that raise serum uric acid levels and lower urine uric acid levels).
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.
Following the identification of increased risks of heart attacks with the selective COX-2 inhibitorrofecoxib 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 nonusers. 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 found no additional cardiovascular risk from diclofenac use. A very large study of 1,028,437 Danish users of various NSAIDs or coxibs found the "Use of the nonselective NSAID diclofenac and the selective cyclooxygenase-2 inhibitor rofecoxib was associated with an increased risk of cardiovascular death (odds ratio, 1.91; 95% confidence interval, 1.62 to 2.42; and odds ratio, 1.66; 95% confidence interval, 1.06 to 2.59, respectively), with a dose-dependent increase in risk." In Britain the Medicines and Healthcare Products Regulatory Agency (MHRA) said in June 2013 that the drug should not be used by people with serious underlying heart conditions—people who had suffered heart failure, heart disease or a stroke were advised to stop using it completely. As of January 15 2015 the MHRA announced that diclofenac will be reclassified as a prescription-only medicine (POM) due to the risk of cardiovascular adverse events.
Gastrointestinal complaints are most often noted. The development of ulceration and/or bleeding requires immediate termination of treatment with diclofenac. Most patients receive a gastro-protective drug as prophylaxis during long-term treatment (misoprostol, ranitidine 150 mg at bedtime or omeprazole 20 mg at bedtime).
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 more hepatotoxic than other NSAIDs.
As of December 2009, Endo, Novartis, and the US FDA notified healthcare professionals to add new warnings and precautions about the potential for elevation in liver function tests during treatment with all products containing diclofenac sodium.
Cases of drug-induced hepatotoxicity have been reported in the first month, but can occur at any time during treatment with diclofenac. Postmarketing surveillance has reported cases of severe hepatic reactions, including liver necrosis, jaundice, fulminant hepatitis with and without jaundice, and liver failure. Some of these reported cases resulted in fatalities or liver transplantation.
Physicians should measure transaminases periodically in patients receiving long-term therapy with diclofenac. Based on clinical trial data and postmarketing experiences, transaminases should be monitored within 4 to 8 week after initiating treatment with diclofenac.
Studies in Pakistan showed diclofenac caused acute kidney failure in vultures when they ate the carcasses of animals that had recently been treated with it. Drug-sensitive species and individual humans 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 nonsensitive persons if resistance to side effects decreases with age. However, this side effect cannot 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."
Mental health side effects have been reported. These symptoms are rare, but exist in significant enough numbers to include as potential side effects. These include depression, anxiety, irritability, nightmares, and psychotic reactions.
Diclofenac and other NSAIDs can cause temporary infertility in women, particularly those who take it regularly. NSAIDs have been known to cause luteinized unruptured follicle syndrome, which delays or prevents ovulation.
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.
It induces warm antibody hemolytic anemia by inducing antibodies to Rh antigens; ibuprofen also does this.
Diclofenac may disrupt the normal menstrual cycle.
Research (published 2010) has linked use of diclofenac to an increased risk of stroke.
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 hr) than the very short half-life of the drug indicates. This could be partly because it persists for over 11 hours in synovial fluids.
Diclofenac may also be a unique member of the NSAIDs. Some evidence indicates it inhibits the lipoxygenase pathways, thus reducing formation of the leukotrienes (also pro-inflammatory autacoids). It also may inhibit phospholipase A2 as part of its mechanism of action. These additional actions may explain its high potency - it is the most potent NSAID on a broad basis.
Marked differences exist among NSAIDs in their selective inhibition of the two subtypes of cyclooxygenase, COX-1 and COX-2. Much pharmaceutical drug design has attempted to focus on selective COX-2 inhibition as a way to minimize the gastrointestinal side effects of NSAIDs such as aspirin. In practice, use of some COX-2 inhibitors with their adverse effects has led to massive numbers of patient family lawsuits alleging wrongful death by heart attack, yet other significantly COX-selective NSAIDs, such as diclofenac, have been well tolerated by most of the population.
Besides the well-known and often-cited COX-inhibition, a number of other molecular targets of diclofenac possibly contributing to its pain-relieving actions have recently been identified. These include:
Blockage of voltage-dependent sodium channels (after activation of the channel, diclofenac inhibits its reactivation also known as phase inhibition)
Use of diclofenac in animals has been reported to have led to a sharp decline in the vulture population in the Indian subcontinent – a 95% decline by 2003 and a 99.9% decline by 2008. The mechanism is presumed to be renal failure, a known side effect of diclofenac. Vultures eat the carcasses of livestock that have been administered veterinary diclofenac, and are poisoned by the accumulated chemical, as vultures do not have a particular enzyme to break down diclofenac. At a meeting of the National Wildlife Board in March 2005, the Government of India announced it intended to phase out the veterinary use of diclofenac.Meloxicam is a safer candidate to replace use of diclofenac. It is more expensive than diclofenac, but the price is coming down as more drug companies begin to manufacture it.
"The loss of tens of millions of vultures over the last decade has had major ecological consequences across the Indian Subcontinent that pose a potential threat to human health. In many places, populations of feral dogs (Canis familiaris) have increased sharply from the disappearance of Gyps vultures as the main scavenger of wild and domestic ungulate carcasses. Associated with the rise in dog numbers is an increased risk of rabies" and casualties of almost 50,000 people. The Government of India cites this as one of those major consequences of a vulture species extinction. A major shift in transfer of corpse pathogens from vultures to feral dogs and rats could lead to a disease pandemic causing millions of deaths in a crowded country like India; whereas vultures’ digestive systems safely destroy many species of such pathogens.
The loss of vultures has had a social impact on the Indian Zoroastrian Parsi community, who traditionally use vultures to dispose of human corpses in Towers of Silence, but are now compelled to seek alternative methods of disposal.
The resulting multiplication of feral dogs in India and Pakistan has caused a multiplication of leopards feeding on those dogs and invading urban areas looking for dogs as prey, resulting in occasional attacks on human children.
Diclofenac has been recently authorised for use on cattle and pigs in Italy, and, since 2013, in Spain where 90% of European vultures live, and this product is now becoming widely available in other EU countries. 
Pennsaid is a minimally systemic prescription topical lotion formulation of 1.5% w/w diclofenac sodium, which is approved in the US, Canada and other countries for osteoarthritis of the knee.
Flector Patch, a minimally systemic topical patch formulation of diclofenac, is indicated for acute pain due to minor sprains, strains, and contusions. The patch has been approved in many other countries outside the US under different brand names.
Voltaren and Voltarol contain the sodium salt of diclofenac. In the United Kingdom, Voltarol can be supplied with either the sodium salt or the potassium salt, while Cataflam, sold in some other countries, is the potassium salt only. However, Voltarol Emulgel contains diclofenac diethylammonium, in which a 1.16% concentration is equivalent to a 1% concentration of the sodium salt.
Diclofenac is available in stomach acid-resistant formulations (25 and 50 mg), fast-disintegrating oral formulations (25 and 50 mg), powder for oral solution (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 in some countries: 12.5 mg diclofenac as potassium salt in Switzerland (Voltaren dolo), the Netherlands (Voltaren K), and preparations containing 25 mg diclofenac as the potassium salt in Germany (various trade names), New Zealand, Australia, Japan, (Voltaren Rapid), and Sweden (Voltaren T and Diclofenac T). Diclofenac as potassium salt can be found throughout the Middle East in 25-mg and 50-mg doses (Cataflam). Solaraze (3% diclofenac sodium gel) is topically applied, twice a day for three months, to manage the skin condition known as actinic or solar keratosis. Parazone-DP is combination of diclofenac potassium and paracetamol, manufactured and supplied by Ozone Pharmaceuticals and Chemicals, Gujarat,India.
On the 14th of january 2015, Diclofenac oral preparations were re-classified as Prescription Only Medicines in the UK. The topical preparations are still available without prescription.
Diclofenac formulations are available worldwide under many different trade names.
^Mazumdar K, Dutta NK, Dastidar SG, Motohashi N, Shirataki Y (2006). "Diclofenac in the management of E. coli urinary tract infections". In Vivo20 (5): 613–619. PMID17091768.
^Dutta NK, Annadurai S, Mazumdar K, Dastidar SG, Kristiansen JE, Molnar J, Martins M, Amaral L (2007). "Potential management of resistant microbial infections with a novel non-antibiotic: the anti-inflammatory drug diclofenac sodium". Int. J. Antimicrob. Agents30 (3): 242–249. doi:10.1016/j.ijantimicag.2007.04.018. PMID17644318.
^Dutta NK, Mazumdar K, Dastidar SG, Park JH (2007). "Activity of diclofenac used alone and in combination with streptomycin against Mycobacterium tuberculosis in mice". Int. J. Antimicrob. Agents30 (4): 336–340. doi:10.1016/j.ijantimicag.2007.04.016. PMID17644321.
^Naidoo V, Swan GE (August 2008). "Diclofenac toxicity in Gyps vulture is associated with decreased uric acid excretion and not renal portal vasoconstriction". Comp. Biochem. Physiol. C Toxicol. Pharmacol.149 (3): 269–74. doi:10.1016/j.cbpc.2008.07.014. PMID18727958.
^Solomon DH, Avorn J, Stürmer T, Glynn RJ, Mogun H, Schneeweiss S (2006). "Cardiovascular outcomes in new users of coxibs and nonsteroidal antiinflammatory drugs: high-risk subgroups and time course of risk". Arthritis Rheum54 (5): 1378–89. doi:10.1002/art.21887. PMID16645966.
^Dastidar SG, Ganguly K, Chaudhuri K, Chakrabarty AN (2000). "The anti-bacterial action of diclofenac shown by inhibition of DNA synthesis". Int. J. Antimicrob. Agents14 (3): 249–51. doi:10.1016/S0924-8579(99)00159-4. PMID10773497.
^Fowler PD, Shadforth MF, Crook PR, John VA (1983). "Plasma and synovial fluid concentrations of diclofenac sodium and its major hydroxylated metabolites during long-term treatment of rheumatoid arthritis". Eur. J. Clin. Pharmacol.25 (3): 389–94. doi:10.1007/BF01037953. PMID6628528.
^Scholer. Pharmacology of Diclofenac Sodium. Am J of Medicine Volume 80 April 28, 1986
^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 (2004). "Diclofenac residues as the cause of vulture population decline in Pakistan". Nature427 (6975): 630–3. Bibcode:2004Natur.427..630O. doi:10.1038/nature02317. PMID14745453.
^Schwaiger J, Ferling H, Mallow U, Wintermayr H, Negele RD (2004). "Toxic effects of the non-steroidal anti-inflammatory drug diclofenac. Part I: Histopathological alterations and bioaccumulation in rainbow trout". Aquat. Toxicol68 (2): 141–150. doi:10.1016/j.aquatox.2004.03.014. PMID15145224.
^Triebskorn R, Casper H, Heyd A, Eikemper R, Köhler HR, Schwaiger J (2004). "Toxic effects of the non-steroidal anti-inflammatory drug diclofenac. Part II: Cytological effects in liver, kidney, gills and intestine of rainbow trout (Oncorhynchus mykiss)". Aquat. Toxicol68 (2): 151–166. doi:10.1016/j.aquatox.2004.03.015. PMID15145225.