DFS 1.5%/MS 25%/MENTH 6%/CAP 0.025% PAK (Page 4 of 7)

11. DESCRIPTION

Diclofenac sodium topical solution is a clear, colorless to faintly pink-orange solution for topical application.

Diclofenac sodium topical solution contains 1.5% w/w diclofenac sodium, a benzeneacetic acid derivative that is a nonsteroidal anti-inflammatory drug (NSAID), designated chemically as 2-[(2,6-dichlorophenyl)amino]-benzeneacetic acid, monosodium salt. The molecular weight is 318.14. Its molecular formula is C 14 H 10 Cl 2 NNaO 2 and it has the following structural formula:

Chemical Structure
(click image for full-size original)

Each 1 mL of solution contains 16.05 mg of diclofenac sodium. In addition diclofenac sodium topical solution contains the following inactive ingredients: dimethyl sulfoxide USP (DMSO, 45.5% w/w), propylene glycol, alcohol, glycerin and purified water.

12. CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

The mechanism of action of diclofenac is similar to that of other nonsteroidal anti-inflammatory drugs. Diclofenac inhibits the enzyme, cyclooxygenase (COX), an early component of the arachidonic acid cascade, resulting in the reduced formation of prostaglandins, thromboxanes and prostacylin. It is not completely understood how reduced synthesis of these compounds results in therapeutic efficacy.

12.2 Pharmacodynamics

Diclofenac, the active component of diclofenac sodium topical solution has anti-inflammatory, anti-nociception, and antipyretic effects.

12.3 Pharmacokinetics

After topical administration to healthy human volunteers of single and multiple maximum doses of diclofenac sodium topical solution, 40 drops (approximately 1.2 mL) to each knee (80 drops total dose), the following diclofenac pharmacokinetic parameters were obtained: (see Table 2).

Table 2: Single-Dose (80 drops) and Multiple Dose (80 drops four times daily for 7 days) Diclofenac Sodium Topical Solution Pharmacokinetic Parameters
Pharmacokinetic Parameters Diclofenac sodium
Normal Adults [N=18] (Age: 18-55 years) Normal Adults [N=19] (Age: 18-55 years)
Single Dose Multiple Dose Four times daily for 7 days
*
Apparent total body clearance
AUC 0-t 177.5 ± 72.6 ng.h/mL 695.4 ± 348.9 ng.h/mL
AUC 0-inf 196.3 ± 68.5 ng.h/mL 745.2 ± 374.7 ng.h/mL
Plasma C max 8.1 ± 5.9 ng/mL 19.4 ± 9.3 ng/mL
Plasma T max (h) 11.0 ± 6.4 4.0 ± 6.5
Plasma t 1/2 (h) 36.7 ± 20.8 79.0 ± 38.1
Kel (h -1) 0.024 ± 0.010 0.011 ± 0.004
CL/F (L/h) 244.7 ± 84.7 *

Absorption

Diclofenac systemic exposure from diclofenac sodium topical solution application (4 times daily for 1 week) was approximately 1/3 of the diclofenac systemic exposure from the Solaraze (diclofenac topical gel) application (twice daily for 4 weeks).

Distribution

Diclofenac is more than 99% bound to human serum proteins, primarily to albumin.

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.

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 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.

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.

Special Populations

Pediatric: The pharmacokinetics of diclofenac sodium topical solution has not been investigated in pediatric patients.

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

12.4 Platelets

The effect of diclofenac sodium topical solution on platelet function was evaluated in 10 healthy human volunteers as a sub-study of a multiple-dose pharmacokinetic study [see Pharmacokinetics (12.3)]. Average (range) platelet aggregation time following stimulation with adenosine diphosphate, collagen, epinephrine and arachidonic acid was 101.3% (73.3 to 128.1), 99.8% (69.6 to 112.9), 109.9% (66.2 to 178.1) and 99.0% (15.5 to 126.6) of baseline value, respectively. These results indicate that there was no effect on platelet aggregation after application of the maximum clinical dose for 7 days [see Pharmacokinetics (12.3)].

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