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Mechanism of Action
Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID). In pharmacologic studies, diclofenac has shown anti-inflammatory, analgesic, and antipyretic activity. As with other NSAIDs, its mode of action is not known; its ability to inhibit prostaglandin synthesis, however, may be involved in its anti-inflammatory activity, as well as contribute to its efficacy in relieving pain associated with inflammation.
Flector Patch applied to intact skin provides local analgesia by releasing diclofenac epolamine from the patch into the skin.
Following a single application of the Flector Patch (diclofenac epolamine topical patch) on the upper inner arm, peak plasma concentrations of diclofenac (range 0.7 - 6 ng/mL) were noted between 10 - 20 hours of application. Plasma concentrations of diclofenac in the range of 1.3 - 8.8 ng/mL were noted after five days with twice-a-day Flector Patch (diclofenac epolamine topical patch) application.
Systemic exposure (AUC) and maximum plasma concentrations of diclofenac, after repeated dosing for four days with Flector Patch (diclofenac epolamine topical patch) , were lower ( < 1%) than after a single oral 50-mg diclofenac sodium tablet.
The pharmacokinetics of Flector Patch (diclofenac epolamine topical patch) has been tested in healthy volunteers at rest or undergoing moderate exercise (cycling 20 min/h for 12 h at a mean HR of 100.3 bpm). No clinically relevant differences in systemic absorption were observed, with peak plasma concentrations in the range of 2.2 - 8.1 ng/mL while resting, and 2.7 - 7.2 ng/mL during exercise.
Diclofenac has a very high affinity ( > 99%) for human serum 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.
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.
The plasma elimination half-life of diclofenac after application of Flector Patch (diclofenac epolamine topical patch) is approximately 12 hours. 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.
Efficacy of Flector Patch (diclofenac epolamine topical patch) was demonstrated in two of four studies of patients with minor sprains, strains, and contusions. Patients were randomly assigned to treatment with the Flector Patch (diclofenac epolamine topical patch) , or a placebo patch identical to the Flector Patch minus the active ingredient. In the first of these two studies, patients with ankle sprains were treated once daily for a week. In the second study, patients with sprains, strains and contusions were treated twice daily for up to two weeks. Pain was assessed over the period of treatment. Patients treated with the Flector Patch (diclofenac epolamine topical patch) experienced a greater reduction in pain as compared to patients randomized to placebo patch as evidenced by the responder curves presented below.
Figure 1: Patients Achieving Various Levels of Pain Relief
at Day 3; 14-Day Study
Figure 2: Patients Achieving Various Levels of Pain Relief
at End of Study; 14-Day Study
Figure 3: Patients Achieving Various Levels of Pain Relief
at Day 3; 7-Day Study
Figure 4: Patients Achieving Various Levels of Pain Relief
at End of Study; 7-Day Study
Last reviewed on RxList: 3/18/2011
This monograph has been modified to include the generic and brand name in many instances.
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