Diclofenac Sodium

DICLOFENAC SODIUM- diclofenac sodium tablet, delayed release
BluePoint Laboratories

Rx only

WARNING: RISK OF SERIOUS CARDIOVASCULAR AND GASTROINTESTINAL EVENTS

Cardiovascular Thrombotic Events

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause an increased risk of serious cardiovascular thrombotic events, including myocardial infarction and stroke, which can be fatal. This risk may occur early in treatment and may increase with duration of use (see WARNINGS).
Diclofenac sodium delayed-release tablets are contraindicated in the setting of coronary artery bypass graft (CABG) surgery (see CONTRAINDICATIONS and WARNINGS).

Gastrointestinal Bleeding, Ulceration, and Perforation

NSAIDs cause an increased risk of serious gastrointestinal (GI) adverse events including bleeding, ulceration, and perforation of the stomach or intestines, which can be fatal. These events can occur at any time during use and without warning symptoms. Elderly patients and patients with a prior history of peptic ulcer disease and/or GI bleeding are at greater risk for serious GI events (see WARNINGS).

DESCRIPTION

Diclofenac sodium is a benzeneacetic acid derivative, designated chemically as 2-[(2,6-dichlorophenyl)amino] benzeneacetic acid, monosodium salt. The structural formula is:

structural formula

C14 H10 Cl2 NNaO2 M.W. 318.14

Diclofenac sodium is a white to off-white, hygroscopic crystalline powder. It is freely soluble in methanol, soluble in ethanol, sparingly soluble in water and practically insoluble in chloroform and in dilute acid. The n-octanol/water partition coefficient is 13.4 at pH 7.4 and 1545 at pH 5.2. Diclofenac sodium has a dissociation constant (pKa) of 4.0 ± 0.2 at 25°C in water.

Each enteric-coated tablet for oral administration contains 25 mg, 50 mg, or 75 mg of diclofenac sodium. In addition, each tablet contains the following inactive ingredients. Inactive ingredients: lactose (monohydrate), microcrystalline cellulose, croscarmellose sodium, povidone, talc, magnesium stearate, methacrylic acid copolymer, polyethylene glycol, opadry brown (Titanium dioxide, hypromellose, polyethylene glycol, iron oxide red, iron oxide yellow).

CLINICAL PHARMACOLOGY

Mechanism of Action

Diclofenac has analgesic, anti-inflammatory, and antipyretic properties.

The mechanism of action of diclofenac sodium delayed-release tablets, like that of other NSAIDs, is not completely understood but involves inhibition of cyclooxygenase (COX-1 and COX-2).

Diclofenac is a potent inhibitor of prostaglandin synthesis in vitro. Diclofenac concentrations reached during therapy have produced in vivo effects. Prostaglandins sensitize afferent nerves and potentiate the action of bradykinin in inducing pain in animal models. Prostaglandins are mediators of inflammation. Because diclofenac is an inhibitor of prostaglandin synthesis, its mode of action may be due to a decrease of prostaglandins in peripheral tissues.

Pharmacokinetics

Absorption

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). Food has no significant effect on the extent of diclofenac absorption. However, there is usually a delay in the onset of absorption of 1 to 4.5 hours and a reduction in peak plasma levels of <20%.

Table 1. Pharmacokinetic Parameters for Diclofenac

Normal Healthy Adults (20-48 years)

PK Parameter

Mean

Coefficient of Variation (%)

Absolute Bioavailability (%)[N = 7]

55

40

Tmax (hr) [N = 56]

2.3

69

Oral Clearance(CL/F; mL/min) [N = 56]

582

23

Renal Clearance(% unchanged drug in urine)[N = 7]

<1

Apparent Volume of Distribution (V/F; L/kg) [N = 56]

1.4

58

Terminal Half-life (hr)[N = 56]

2.3

48

Distribution

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.

Elimination

Metabolism

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 CYP2C9. Both diclofenac and its oxidative metabolites undergo glucuronidation or sulfation followed by biliary excretion. Acylglucuronidation mediated by UGT2B7 and oxidation mediated by CYP2C8 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.

Excretion

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.

Special Populations

Pediatric

The pharmacokinetics of diclofenac sodium delayed-release tablets has not been investigated in pediatric patients.

Race

Pharmacokinetic differences due to race have not been identified.

Hepatic Impairment

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

Renal Impairment

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.

Drug Interactions Studies

Voriconazole

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).

Aspirin

When NSAIDs were administered with aspirin, the protein binding of NSAIDs were reduced, although the clearance of free NSAID was not altered. The clinical significance of this interaction is not known. See Table 2 for clinically significant drug interactions of NSAIDs with aspirin (see PRECAUTIONS: Drug Interactions).

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