Diclofenac inhibits the activity of the enzyme cyclo - oxygenase, resulting in decreased formation of precursors of prostaglandins and thromboxanes from arachidonic acid.
Diclofenac may block pain impulse generation via a peripheral action that may involve reduction of the activity of prostaglandins, and possibly inhibition of the synthesis or actions of other substances that sensitize pain receptors to mechanical or chemical stimulation.

Indicated for rheumatoid arthritis, osteoarthritis, ankylosing spondylitis. 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.

This medication should not be used when the following medical problems exist: Allergic reaction, severe, such as anaphylaxis or angioedema, induced by aspirin or other NSAIDs, history of; Nasal polyps associated with bronchospasm, aspirin - induced (high risk of severe allergic reactions because of cross - sensitivity); Blood dyscrasis, active or history of; Bone marrow depression ( diclofenac may induce or exacerbate these conditions). Risk benefit should be considered when the following medical problems exist:
Allergic reaction, mild, such as allergic rhinitis, urticaria, or skin rash, induced by aspirin or other NSAIDs, history of (possibility of cross - sensitivity); Anemia; Asthma; Hypertension; Edema; Inftammatory or ulcerative disease of the upper or lower gastrointestinal tract; Diabetes mellitus; Hemophilia or other bleeding problems; Hepatic or renal function impairment; Stomatitis; Systemic lupus erythematosus; Porphyria, hepatic (diclofenac may precipitate an acute attack).

Embryotoxicity and other adverse effects, but not teratogenicity, demonstrated in animal studies.
FDA Pregnancy Category B.

Diclofenac is distributed into breast milk.

In addition to the interactions listed below, the possibility should be considered that additive or multiple effects leading to impaired blood clotting and / or increased risk of bleeding may occur if any NSAID is used concurrently with any medication having a significant potential for causing hypoprothrombinemia, thrombocytopenia, or gastrointestinal ulceration or hemorrhage.
Acetaminophen, Alcohol, Potassium supplements, Anticoagulants, Heparin, Thrombolytic agents, Potassium - sparing diuretics, Lithium, Probenecid, Salicylates, Digoxin, Antidiabetic agents or insulin, Corticosteroids, Cyclosporine, Valproic acid.

Hypersensitivity reactions such as: Rhinosinusitis / asthma or angioedema / urticaria; Anaphylaxis.
Gastrointestinal problems; Dermatologic effects; Headache; Renal and hepatic function impairment; Hearing problems; CNS effects; Hyperkalemia; Edema.

1 - Enteric coated tablets:
Usual adult dose:
Rheumatoid arthritis - Oral, 150 to 200 mg per day in 3 or 4 divided doses, initially. Afther a satisfactory response has been obtained, dosage should be reduced to the minimum dose that provides continuing control of symptoms, usually 75 to 100 mg a day in 3 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 continuing control of symptoms.
Usual adult prescribing limits:
Rheumatoid arthritis - 225 mg per day.
Osteoarthritis - 150 mg per day; higher doses have not been studied.
Usual pediatric dose - Safety and efficacy have not been established.
2 - Suppositories:
Usual adult dose: Antirheumatic (nonsteroidal anti - inflammatory) - Rectal, 50 or 100 mg, as a substitute for the last oral dose of the day.
Usual adult prescribing limits:
Total daily dosage (oral and rectal) should not exceed 150 mg.
Usual pediatric dose:
Safety and efficacy have not been established.