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Diclofenac (Diclofenac Potassium) - Description and Clinical Pharmacology



Revised – June 2012

Rx only

Prescribing Information


Diclofenac sodium extended-release tablets, USP are a benzeneacetic acid derivative. The chemical name is 2-[(2,6-dichlorophenyl)amino] benzeneacetic acid, monosodium salt. The molecular weight is 318.13. Its molecular formula is C14H10Cl2NNaO2, and it has the following structural formula

Each extended-release tablet for oral administration contains 100 mg of diclofenac sodium, USP. In addition, each tablet contains the following inactive ingredients: carnauba wax, cetyl alcohol, colloidal silicon dioxide, hypromellose, lactose monohydrate, magnesium stearate, povidone, synthetic yellow iron oxide, talc, titanium dioxide, and triacetin.



Diclofenac sodium extended-release tablets, USP are a non-steroidal anti-inflammatory drug (NSAID) that exhibits anti-inflammatory, analgesic, and antipyretic activities in animal models. The mechanism of action of diclofenac sodium extended-release, like that of other NSAIDs, is not completely understood but may be related to prostaglandin synthetase inhibition.



Diclofenac is 100% absorbed after oral administration compared to IV administration as measured by urine recovery. However, due to first-pass metabolism, only about 50% of the absorbed dose is systemically available (see Table 1). When diclofenac sodium extended-release is taken with food, there is a delay of 1 to 2 hours in the Tmax and a two-fold increase in Cmax values. The extent of absorption of diclofenac, however, is not significantly affected by food intake.

Table 1. Pharmacokinetic Parameters for Diclofenac
   Normal Healthy Adults
 PK Parameter  (18 to 48 yrs.)
     Coefficient of
   Mean  Variation (%)




 Bioavailability (%)

 [N = 7]

 Tmax (hr)



 [N = 12]

 Oral Clearance (CL/F; mL/min)



 [N = 12]

 Renal Clearance

 (% unchanged drug in urine)



 [N = 7]

 Apparent Volume of



 Distribution (V/F; L/kg)

 [N = 56]

 Terminal Half-life (hr)



 [N = 56]


The apparent volume of distribution (V/F) of diclofenac sodium is 1.4 L/kg. Diclofenac is more than 99% bound to human serum proteins, primarily to albumin. Serum protein binding is constant over the concentration range (0.15 to 105 mcg/mL) achieved with recommended doses.

Diclofenac diffuses into and out of the synovial fluid. Diffusion into the joint occurs when plasma levels are higher than those in the synovial fluid, after which the process reverses and synovial fluid levels are higher than plasma levels. It is not known whether diffusion into the joint plays a role in the effectiveness of diclofenac.


Five diclofenac metabolites have been identified in human plasma and urine. The metabolites include 4'-hydroxy-, 5-hydroxy-, 3'-hydroxy-, 4',5-dihydroxy- and 3'-hydroxy-4'-methoxy-diclofenac. The major diclofenac metabolite, 4'-hydroxy-diclofenac, has very weak pharmacologic activity. The formation of 4’-hydroxy diclofenac is primarily mediated by CPY2C9. Both diclofenac and its oxidative metabolites undergo glucuronidation or sulfation followed by biliary excretion. Acylglucuronidation mediated by UGT2B7 and oxidation mediated by CPY2C8 may also play a role in diclofenac metabolism. CYP3A4 is responsible for the formation of minor metabolites, 5-hydroxy- and 3’-hydroxy-diclofenac. In patients with renal dysfunction, peak concentrations of metabolites 4'-hydroxy- and 5-hydroxy-diclofenac were approximately 50% and 4% of the parent compound after single oral dosing compared to 27% and 1% in normal healthy subjects.


Diclofenac is eliminated through metabolism and subsequent urinary and biliary excretion of the glucuronide and the sulfate conjugates of the metabolites. Little or no free unchanged diclofenac is excreted in the urine. Approximately 65% of the dose is excreted in the urine and approximately 35% in the bile as conjugates of unchanged diclofenac plus metabolites. Because renal elimination is not a significant pathway of elimination for unchanged diclofenac, dosing adjustment in patients with mild to moderate renal dysfunction is not necessary. The terminal half-life of unchanged diclofenac is approximately 2 hours.

Drug Interactions

When co-administered with voriconazole (inhibitor of CYP2C9, 2C19 and 3A4 enzyme), the Cmax and AUC of diclofenac increased by 114% and 78%, respectively (see PRECAUTIONS, Drug Interactions).

Special Populations

Pediatric: The pharmacokinetics of diclofenac sodium extended-release has not been investigated in pediatric patients.

Race: Pharmacokinetic differences due to race have not been identified.

Hepatic Insufficiency: Hepatic metabolism accounts for almost 100% of diclofenac sodium extended-release elimination, so patients with hepatic disease may require reduced doses of diclofenac sodium extended-release compared to patients with normal hepatic function.

Renal Insufficiency: Diclofenac pharmacokinetics has been investigated in subjects with renal insufficiency. No differences in the pharmacokinetics of diclofenac have been detected in studies of patients with renal impairment. In patients with renal impairment (inulin clearance 60 to 90, 30 to 60, and <30 mL/min; N=6 in each group), AUC values and elimination rate were comparable to those in healthy subjects.

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