Diclofenac inhibits prostaglandin synthesis by decreasing the activity of enzyme cyclooxygenase, which results in decreased formation of prostaglandin precursors from arachidonic acid.

Diclofenac is used mainly for the relief of pain and inflammation in various conditions: musculoskeletal and joint disorders such as rheumatoid arthritis, osteoarthritis, and ankylosing spondylitis; peri-articular disorders such as bursitis and tendinitis; soft-tissue disorders such as sprains or strains; and other painful conditions such as renal colic, acute gout, dysmenorrhea, migraine, and following some surgical procedures.
Immediate–release tablets only indicated for pain and primary dysmenorrhea, and may also be used to relieve acute attacks of gout or calcium pyrophosphate deposition disease (pseudogout) and pain associated with nonrheumatic inflammatory conditions or vascular headaches.
Delayed-release tablets and capsules are used for chronic treatment of rheumatoid arthritis and osteoarthritis.
Diclofenac topical gel is used for tendinitis, post-operation or post–trauma edema, and relief of local pain and inflammation.

Abdominal cramps and pain; Constipation; Diarrhea; Flatulence; Indigestion; Nausea; Peptic ulcer/GI bleeding; Pancreatitis; Vomiting; Increased ALT/AST; Cirrhosis; Hepatic necrosis; Headache; Dizziness; Pruritus; Rash; Alopecia; Photosensitivity; Fluid retention; Acute renal failure; Aseptic meningitis; Agranulocytosis; Aplastic anemia; Thrombocytopenia; Leukopenia; Anaphylaxis; Asthma ; Angioedema; Eosinophilia; Erythema multiforme major; Hearing loss; Visual changes; Nephrotic syndrome; Local reactions to be caused by rectal administration including itching, burning, exacerbation of hemorrhoids.

Hypersensitivity to diclofenac, any component of the formulation, aspirin or other NSAIDs; Porphyria; Pregnancy (3rd trimester)

Use with caution in patients with CHF, dehydration, hypertension, decreased renal or hepatic function, history of GI disease, active GI ulceration or bleeding , pre-existing asthma, or those receiving anticoagulants. Elderly are at a high risk for adverse effects from NSAIDs; therefore use lowest effective dose for shortest period possible. Withhold for at least 4-6 half-lives prior to surgical or dental procedures.

Concurrent use with diclofenac may decrease the antihypertensive effects of ACE inhibitors, angiotensin II antagonists, loop diuretics, thiazides and hydralazine. Anticoagulants and antiplatelet drugs can cause an increased risk of bleeding. Cholestyramine and colestipol reduce the bioavailability of diclofenac. Corticosteroids may increase the risk of GI ulceration; avoid concurrent use. NSAIDs may increase serum creatinine and cyclosporine level; monitor cyclosporine levels and renal function. Lithium levels can be increased; avoid concurrent use or monitor lithium levels. Avoid use during moderate or high-dose methotrexate (increased and prolonged methotrexate levels). Verapamil plasma concentration is decreased; avoid concurrent use. Sucralfate decreases the plasma concentration of diclofenac.

Monitor CBC, liver enzymes, urine output and serum BUN/creatinine , occult blood loss, hemoglobin, hematocrit.

Diclofenac may be taken with food to decrease GI distress.

Usual adult dose:
1- Enteric coated tablets:
Analgesic and Antidysmenorrheal–Oral, 50 mg three times a day as needed. If necessary, 100 mg may be administered to the first dose only.
Rheumatoid arthritis–Oral, 150 to 200 mg per day in 3 or 4 divided doses, initially. After a satisfactory response has been obtained, dosage should be reduced to 75 to 100 mg a day in three divided doses.
Osteoarthritis–Oral, 100 to 150 mg per day in 2 or 3 divided doses, initially. After a satisfactory response has been obtained, dosage should be reduced to the minimum dose that provides continuing control of symptoms.
Ankylosing spondylitis–Oral, 100 to 125 mg a day in 4 or 5 divided doses, initially. After a satisfactory response has been obtained, dosage should be reduced to the minimum dose that provides continung control of symptoms.

Usual adult prescribing limits:
Analgesic and Antidysmenorrheal–Up to 200 mg on the first day, then 150 mg per day thereafter.
Rheumatoid arthritis–225 mg per day.
Osteoarthitis–150 mg per day.

2- S.R. tablets:
Rheumatoid arthritis–Oral, 100 mg once a day, in the morning or evening.
Osteoarthritis–Oral, 100-200 mg once a day, in the morning or evening.
The sustained-release dosage form is not intended as initial therapy; the daily maintenance dose should be determined using an immediate or delayed- release formulation. Then, the sustained-release dosage form may be used.
The sustained–release tablets are to be swallowed whole, not crushed or chewed.

3- Suppositories:
Antirheumatic (nonsteroidal anti-inflammatory)–Rectal, 50 or 100 mg, as a substitute for the last oral dose of the day.
Total daily dosage (oral and rectal) should not exceed 150 mg.

4- Topical:
Usual adult, adolescent, children (15 years of age and over):
It is applied to the affected site 3 to 4 times daily ; Treatment should be reviewed after 14 days or after 28 days if used for osteoarthritis.
Usual pediatric dose:
Safety and efficacy have not been established.

• Enteric Coated Tablet: 25 mg , 50 mg
  Sustained–release Tablet (Diclokim®), 100 mg
• Suppository: 50 mg , 100 mg
• Topical Gel 1%: 60 grams

• USP DI, 2004
• Up To Date, Vol. 13.1 (2005)
• Martindale, The Complete Drug Reference, 33 rd edition 2002