Diclofenac – Dosage

What is diclofenac?

Diclofenac is a phenylacetic acid derivative and non-steroidal anti-inflammatory drug (NSAID). NSAIDs inhibit cyclooxygenase (COX)-1 and-2 which are the enzyme responsible for producing prostaglandins (PGs). PGs contribute to inflammation and pain signalling. Diclofenac, like other NSAIDs, is often used as first line therapy for acute and chronic pain and inflammation from a variety of causes. It was the product of rational drug design based on the structures of phenylbutazone, mefenamic acid, and indomethacin. The addition of two chlorine groups in the ortho position of the phenyl ring locks the ring in maximal torsion which appears to be related to increased potency. It is often used in combination with misoprostol to prevent NSAID-induced gastric ulcers. Diclofenac was first approved by the FDA in July 1988 under the trade name Voltaren, marketed by Novartis (previously Ciba-Geigy).

Properties and Characteristics of Diclofenac

Drug class Nonsteroidal anti-inflammatory drug
Brand Names  Voltaren, Cataflam, Voltaren-XR, Cambia, Zipsor, Zorvolex, Dicloflex, Diclomax, Econac, Fenactol, Motifene
Synonyms Diclofenac, Diclofenac acid, Diclofenaco, Diclofenacum
Molecular Formula     C14H11Cl2NO2
Molecular Weight        296.149 g/mol
IUPAC Names 2-{2-[(2,6-dichlorophenyl)amino]phenyl}acetic acid
Structural formula of main components Diclofenac Structural Formula.png
Pure active ingredient Diclofenac
Appearance white to off-white crystalline and slightly hygroscopic powder.
Melting point 283-285 °C
Solubility         2.37 mg/L (at 25 °C)
Excretion Urinary excretion
Available as     Tablets, Gel, Patch, Suspension, Solution
Storage It should be stored at 25 °C but may be exposed to temperatures ranging from 15-30 °C. Diclofenac gel should not be frozen.
Prescription Doctor prescription is required before consumption

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Diclofenac uses

The Food and Drug Administration (FDA) approves prescription drugs such as diclofenac to treat certain conditions. Diclofenac tablets may also be used off-label for other conditions. Off-label drug use is when an FDA-approved drug is prescribed for a purpose other than what it’s approved for.

  • Diclofenac for osteoarthritis: Diclofenac may be prescribed to treat osteoarthritis. Both diclofenac delayed-release (DR) tablets and extended-release (ER) tablets are approved for this use. (With DR tablets, the drug releases once it enters your stomach. With ER tablets, the drug releases into your body over time.)
  • Diclofenac for rheumatoid arthritis: Diclofenac is prescribed to treat rheumatoid arthritis (RA). Both diclofenac DR tablets and ER tablets are approved for this use.
  • Diclofenac for ankylosing spondylitis: Diclofenac DR tablets are approved for treating ankylosing spondylitis (AS). Diclofenac ER tablets are not approved for treating AS.

Diclofenac side effects

Diclofenac can cause mild or serious side effects. The following list contains some of the key side effects that may occur while taking Diclofenac. This list does not include all possible side effects. For more information on the possible side effects of Diclofenac, or tips on how to deal with a troubling side effect, talk with your doctor or pharmacist.

Diclofenac can also cause other side effects.

More common side effects

The more common side effects that can occur with diclofenac gel include:

  • Itching or rash at application site
  • Stomach pain
  • Constipation
  • Diarrhea
  • Gas
  • Heartburn
  • Nausea
  • Vomiting
  • Sleepiness

Serious side effects

Call your doctor right away if you have serious side effects. Serious side effects and their symptoms can include the following:

  • Allergic reaction. Symptoms can include:
    • Itching
    • Rash
    • Breathing problems
    • Hives
  • Edema. Symptoms can include:
    • Swelling of the feet or ankles
    • Increased blood pressure
    • Increased weight
  • Stomach ulcer or stomach bleeding. Symptoms can include:
    • Very dark stools
    • Blood in your stool
  • Bruising more easily.

Mechanism of action

As with most NSAIDs, the primary mechanism responsible for its anti-inflammatory, antipyretic, and analgesic action is thought to be inhibition of prostaglandin synthesis through COX-inhibition. Diclofenac inhibits COX-1 and COX-2 with relative equipotency.

The main target in inhibition of prostaglandin synthesis appears to be 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.

It has a relatively high lipid solubility, making it one of the few NSAIDs that are able to enter the brain by crossing the blood-brain barrier. In the brain, too, it is thought to exert its effect through inhibition of COX-2. In addition, it may have effects inside the spinal cord.

Diclofenac may be a unique member of the NSAIDs in other aspects. 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.

What other drugs will affect diclofenac?

Ask your doctor before using diclofenac if you take an antidepressant. Taking certain antidepressants with an NSAID may cause you to bruise or bleed easily.

Tell your doctor about all your other medicines, especially:

  • Heart or blood pressure medication, including a diuretic or “water pill”;
  • Other forms of diclofenac (Arthrotec, Flector, Pennsaid, Solaraze, Voltaren Gel);
  • A blood thinner – warfarin, Coumadin, Jantoven; or
  • Other NSAIDs – aspirin, ibuprofen (Advil, Motrin), naproxen (Aleve), celecoxib (Celebrex), indomethacin, meloxicam, and others.

This list is not complete. Other drugs may interact with diclofenac, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

How and when to take or use diclofenac?

Always follow the advice of a pharmacist or doctor, and the instructions that come with your medicine.

Diclofenac tablets, capsules and suppositories


You’ll usually take diclofenac tablets, capsules or suppositories 2 to 3 times a day.

The usual dose is 75mg to 150mg a day, depending on what your doctor prescribes for you. Follow your doctor’s advice on how many tablets to take, and how many times a day.

If your doctor prescribes diclofenac for your child, they’ll use your child’s weight to work out the right dose for them.

If you have pain all the time, your doctor may recommend slow-release diclofenac tablets or capsules. You’ll usually take these either once a day in the evening, or twice a day. If you’re taking slow-release diclofenac twice a day, leave a gap of 10 to 12 hours between your doses.

How to take tablets and capsules

Swallow diclofenac tablets or capsules with a drink of milk. If you need to take them with water, take them after a meal or snack. Taking them with milk or food means they’ll be less likely to upset or irritate your stomach.

Swallow them whole, do not crush, break or chew them.

How to use suppositories

Suppositories are medicine that you push gently into your anus (bottom).

  • Go to the toilet beforehand if you need to.
  • Wash your hands before and after using the medicine. Also clean around your anus with mild soap and water, rinse and pat dry.
  • Unwrap the suppository.
  • Gently push the suppository into your anus with the pointed end first. It needs to go in about 3 centimetres (1 inch).
  • Sit or lie still for about 15 minutes. The suppository will melt inside your anus. This is normal.

Diclofenac gel


You’ll usually use the gel 2 to 4 times a day, depending on how strong it is. Check the packaging for more information or speak to your pharmacist.

If you’re using the gel twice a day, use it once in the morning and once in the evening. If you’re using it 3 or 4 times a day, wait at least 4 hours before putting on any more.

The amount of gel you need depends on the size of the area you want to treat. You’ll usually use an amount about the size of a 1 penny or 2 pence piece (2 to 4 grams).

How to use the gel

  1. Gently squeeze the tube, or press firmly and evenly on the nozzle of the dispenser, to get a small amount of gel.
  2. Put the gel on the painful or swollen area and slowly rub it in. It may feel cool on your skin. Wash your hands afterwards.

Diclofenac plasters and patches


Treat only 1 painful area at a time. Do not use more than 2 medicated plasters or patches in any 24-hour period.

How to use plasters and patches

  1. Stick a medicated plaster or patch over the painful area twice a day, once in the morning and once in the evening. Take the old patch off before you put the new one on.
  2. Apply gentle pressure with the palm of your hand until it’s completely stuck to your skin.
  3. When you want to take the plaster or patch off, it helps to moisten it with some water first. Once you have taken it off, wash the affected skin and rub it gently in circular movements to remove any leftover glue.

In case of emergency/overdose

In case of overdose, call the poison control helpline from your locality. If the victim has collapsed, had a seizure, has trouble breathing, or can’t be awakened, immediately call nearby emergency services.

Symptoms of overdose may include:

  • Nausea
  • Vomiting
  • Stomach pain
  • Bloody, black, or tarry stools
  • Vomiting a substance that is bloody or looks like coffee grounds
  • Drowsiness
  • Slow, shallow, or irregular breathing
  • Loss of consciousness

Before taking this medicine (Precautions)

Diclofenac can increase your risk of fatal heart attack or stroke, even if you don’t have any risk factors. Do not use this medicine just before or after heart bypass surgery (coronary artery bypass graft, or CABG).

Diclofenac may also cause stomach or intestinal bleeding, which can be fatal. These conditions can occur without warning while you are using this medicine, especially in older adults.

You should not use diclofenac if you are allergic to it, or if you have ever had an asthma attack or severe allergic reaction after taking aspirin or an NSAID.

Do not use Cambia to treat a cluster headache. Do not use Zipsor if you are allergic to beef or beef protein.

To make sure this medicine is safe for you, tell your doctor if you have:

  • Heart disease, high blood pressure;
  • Ulcers or bleeding in your stomach;
  • Asthma;
  • Liver or kidney disease; or
  • If you smoke.

Diclofenac and pregnancy

Similar to other nonsteroidal anti-inflammatory drugs (NSAIDs), it isn’t safe to take diclofenac at week 30 of pregnancy and beyond. This is because NSAIDs can cause harm if used at this point in pregnancy. Specifically, NSAID use during pregnancy may affect the amount of nutrients that reach the developing fetus. It may also cause kidney problems in a newborn.

Due to these risks, your doctor may recommend you do not take diclofenac from week 20 of pregnancy. This is because NSAIDs may cause harm if used between weeks 20 and 30 of pregnancy. And during this period, the risk of harm may be greater if NSAIDs are used for more than 48 hours.

If an NSAID is prescribed for you during this period, your doctor will closely monitor you for any signs of complications. This includes a lack of nutrients reaching the fetus.

Talk with your doctor to learn more about the risks and benefits of taking treatments for your condition during pregnancy.

Diclofenac and fertility

In rare cases, NSAIDs such as diclofenac may cause reversible infertility (temporary inability to become pregnant) in females. This is based on how the drug works. Fertility may return after diclofenac treatment ends.

The drug’s manufacturer hasn’t stated whether diclofenac affects male fertility. If you have questions about how diclofenac may affect your fertility, talk with your doctor.

Diclofenac and breastfeeding

Diclofenac may pass into breast milk. However, it isn’t known if the drug causes side effects in a child who is breastfed. Talk with your doctor to learn more about the risks and benefits of breastfeeding while you’re taking it.

Diclofenac and birth control

It may not be safe to take diclofenac during certain weeks of pregnancy. If you’re sexually active and you or your partner can become pregnant, talk with your doctor about your birth control needs while you’re taking diclofenac.

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