Diclofenac (sold under a number of trade names) is a potent nonsteroidal anti-inflammatory drug (NSAID) taken or applied to reduce inflammation and as an analgesic reducing pain in certain conditions. It is supplied as or contained in medications under a variety of trade names.
The primary mechanism responsible for its anti-inflammatory, antipyretic, and analgesic action is thought to be inhibition of prostaglandin synthesis by inhibition of cycloxygenase-2 (COX-2). Diclofenac inhibits COX-2 with 20-fold more potency than COX-1 and is said to have a lower incidence of gastrointestinal complaints than COX-1 inhibitors such as aspirin. Some evidence indicates it inhibits the lipoxygenase pathways which are related to inflammation,, and possibly phospholipase A2, as well as possibly phase inhibition (blockage) of voltage-dependent sodium channels, blockage of acid-sensing ion channels (ASICs) and positive allosteric modulation of KCNQ- and BK-potassium channels (related to hyperpolarization of the cell membrane). It also appears to exhibit bacteriostatic activity. Diclofenac lasts for around 6–8 hours in the body, possibly as it persists for over 11 hours in synovial fluids.
The name "diclofenac" derives from its chemical name: 2-(2,6-dichloranilino) phenylacetic acid. Diclofenac was first synthesized by Alfred Sallmann and Rudolf Pfister and introduced as Voltaren
by Ciba-Geigy (now Novartis) in 1973, now by Glaxo SmithKline. In the United Kingdom, United States, India, and Brazil diclofenac may be supplied as either the sodium or potassium salt; in China, it is most often supplied as the sodium salt, while in some other countries it is only available as the potassium salt. It 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 of 2015[update], the cost for a typical month of medication in the United States is US$50 to US$100. In European countries, the cost is no more than £8.40 (approx. US$10) for 24 weeks use.
Use of diclofenac for animals is controversial due to toxicity when eaten by scavenging birds that eat dead animals; the drug has been banned for veterinary use in many countries.
Diclofenac is used to treat pain, inflammatory disorders, and dysmenorrhea.
Inflammatory disorders may include musculoskeletal complaints, especially arthritis, rheumatoid arthritis, polymyositis, dermatomyositis, osteoarthritis, dental pain, temporomandibular joint (TMJ) pain, spondylarthritis, ankylosing spondylitis, gout attacks, and pain management in cases of kidney stones and gallstones. An additional indication is the treatment of acute migraines. Diclofenac is used commonly to treat mild to moderate postoperative or post-traumatic pain, in particular when inflammation is also present, and is effective against menstrual pain and endometriosis.
Diclofenac is also available in topical forms and has been found to be useful for osteoarthritis but not other types of long-term musculoskeletal pain.
It may also help with 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 inflammation of the anterior part of the eyes (e.g., postoperative states). Diclofenac eye drops have also been used to manage pain for traumatic corneal abrasion.
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). Diclofenac can be combined with opioids if needed such as a fixed combination of diclofenac and codeine.
(diclofenac) 50 mg enteric coated tablets
Arthrotec (diclofenac and misoprostol) 50 mg tablets
Dyloject (diclofenac) 2 ml for IV and IM administration
Sintofarm (diclofenac) for suppository administration
Diclofenac consumption has been associated with significantly increased vascular and coronary risk in a study including coxib, diclofenac, ibuprofen and naproxen. Upper gastrointestinal complications were also reported. Major adverse cardiovascular events (MACE) were increased by about a third by diclofenac, chiefly due to an increase in major coronary events. Compared with placebo, of 1000 patients allocated to diclofenac for a year, three more had major vascular events, one of which was fatal. Vascular death was increased significantly by diclofenac.
In 2013, a study funded by core grants from the UK Medical Research Council and the British Heart Foundations, and collaboration coordinated by the Clinical Trial Service Unit & Epidemiological Studies Unit (CTSU) at the University of Oxford, UK; major vascular events were increased by about a third by diclofenac (rate ratio 1·41,95% CI 1·12–1·78; p=0·0036), chiefly due to an increase in major coronary events (1·70, 1·19–2·41; p=0·0032). Compared with placebo, of 1000 patients allocated to diclofenac for a year, three more had major vascular events, one of which was fatal. Vascular death was increased significantly by diclofenac (1·65, 0·95–2·85, p=0·0187).
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 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. 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.
A subsequent large study of 74,838 Danish 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."
Another Danish study, at Aarhus University, has made use of the Danish health registry system's data of over 1.3 million diclofenac users to show that subjects beginning use of it had a 50% increased 30-day risk for a composite outcome of Major adverse cardiovascular events (MACE) compared with individuals who didn’t initiate an NSAID or acetaminophen (95% confidence interval for incidence rate ratio, 1.4-1.7). The risk was also significantly elevated when compared with beginning other NSAIDs or acetaminophen: with those starting ibuprofen or acetaminophen, the MACE risk was elevated 20% in diclofenac initiators (95% CI, 1.1-1.3 for both). Initiating diclofenac was associated with 30% greater risk for MACE compared with initiating naproxen (95% CI, 1.1-1.5). In comparison with other NSAIDs, the short half-life of diclofenac means that a supratherapeutic plasma concentration of diclofenac soon after initiation achieves not just cyclooxygenase-2 (COX-2), but also COX-1 inhibition. However, after those high levels fall, patients taking diclofenac spend a substantial period of time with unopposed COX-2 inhibition, a state that is known to be prothrombotic, and also associated with blood pressure elevation, atherogenesis, and worsening of heart failure.
Diclofenac is similar in COX-2 selectivity to celecoxib. A review by FDA Medical Officer David Graham concluded diclofenac does increase the risk of myocardial infarction.
The primary mechanism responsible for its anti-inflammatory, antipyretic, and analgesic action is thought to be inhibition of prostaglandin synthesis by inhibition of the transiently expressed prostaglandin-endoperoxide synthase-2 (PGES-2) also known as cycloxygenase-2 (COX-2). It also appears to exhibit bacteriostatic activity by inhibiting bacterial DNA synthesis.
Inhibition of prostaglandin synthesis occurs systemically resulting in undesirable symptoms such as irritation of the gastric epithelium. This is the main side effect of diclofenac. Diclofenac inhibits COX-2 with 20 times greater potency than the constitutively expressed isoenzyme COX-1 and has, therefore, a somewhat lower incidence of gastrointestinal complaints than noted with aspirin which inhibits COX-1 to a greater extent.
The action of one single dose is much longer (6 to 8 hr) than the very short 1.2–2 hr half-life of the drug would indicate. 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 COX-inhibition, a number of other molecular targets of diclofenac possibly contributing to its pain-relieving actions have recently been identified. These include:
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; however, toxicity may be due to direct inhibition of uric acid secretion in vultures. 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.
Steppe eagles have the same vulnerability to  diclofenac as vultures and may also fall victim to it. Diclofenac has been shown also to harm freshwater fish species such as rainbow trout. In contrast, New World vultures, such as the turkey vulture, can tolerate at least 100 times the level of diclofenac that is lethal to Gyps species.
"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.
Despite the vulture crisis, diclofenac remains available in other countries including many in Europe. It was controversially approved for veterinary use in Spain in 2013 and continues to be available, despite Spain being home to around 90% of the European vulture population and an independent simulation showing that the drug could reduce the population of vultures by 1-8% annually. Spain's medicine agency presented simulations suggesting that the number of deaths would be quite small.
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.
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. In 2016 Voltarol was one of the biggest selling branded over-the-counter medications sold in Great Britain, with sales of £39.3 million.
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. It is sold in Uruguay alone or, in combination with orphenadrine to treat muscle spasms/pain due to injuries (Dicloflex Ion).
On 14 January 2015, diclofenac oral preparations were reclassified 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.