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Qutenza

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Qutenza

CLINICAL PHARMACOLOGY

Mechanism of Action

Capsaicin is an agonist for the transient receptor potential vanilloid 1 receptor (TRPV1), which is an ion channel-receptor complex expressed on nociceptive nerve fibers in the skin. Topical administration of capsaicin causes an initial enhanced stimulation of the TRPV1-expressing cutaneous nociceptors that may be associated with painful sensations. This is followed by pain relief thought to be mediated by a reduction in TRPV1-expressing nociceptive nerve endings [see Pharmacodynamics]. Over the course of several months, there may be a gradual re-emergence of painful neuropathy thought to be due to TRPV1 nerve fiber reinnervation of the treated area.

Pharmacodynamics

Two studies evaluated the pharmacodynamic effects of Qutenza (capsaicin 8% patch) on sensory function and epidermal nerve fiber (ENF) density in healthy volunteers. Consistent with the known pharmacodynamic effects of capsaicin on TRPV1-expressing nociceptive nerve endings, reduced ENF density and minor changes in cutaneous nociceptive function (heat detection and sharp sensation) were noted one week after exposure to Qutenza (capsaicin 8% patch) . ENF density reduction and sensory changes were fully reversible.

Pharmacokinetics

Pharmacokinetic data in humans showed transient, low ( < 5 ng/mL) systemic exposure to capsaicin in about one third of PHN patients following 60-minute applications of Qutenza. The highest plasma concentration of capsaicin detected was 4.6 ng/mL and occurred immediately after Qutenza (capsaicin 8% patch) removal. Most quantifiable levels were observed at the time of Qutenza (capsaicin 8% patch) removal and were below the limit of quantitation 3 to 6 hours after Qutenza (capsaicin 8% patch) removal. No detectable levels of metabolites were observed in any subject.

Clinical Studies

Postherpetic Neuralgia

The efficacy of Qutenza (capsaicin 8% patch) , was established in two 12-week, double-blind, randomized, dose-controlled, multicenter studies. These studies enrolled patients with postherpetic neuralgia (PHN) persisting for at least 6 months following healing of herpes zoster rash and a baseline score of 3-9 on an 11-point Numerical Pain Rating Scale (NPRS) ranging from 0 (no pain) to 10 (worst possible pain). Qutenza (capsaicin 8% patch) and a control patch were each applied as a single 60-minute application. The control used in these studies looked similar to Qutenza (capsaicin 8% patch) but contained a low concentration of the active ingredient, capsaicin (3.2 mcg/cm2, 0.04% w/w) to retain blinding regarding the known application site reactions of capsaicin (such as burning and erythema). The baseline mean pain scores across the 2 studies was approximately 6.0. Patients who entered the study on stable doses of pain-control medications were required to keep dosing stable throughout the duration of the study. Approximately half of the patients were taking concomitant medications including anticonvulsants, non-SSRI antidepressants, or opioids for their PHN at study entry. Prior to study patch application a topical anesthetic was applied to the treatment area for 60 minutes. Patients were permitted to use local cooling and additional analgesic medications for treatment-related discomfort as needed through Day 5. Patients recorded their pain daily in a diary.

PHN Study 1: In this 12-week study, the Qutenza (capsaicin 8% patch) group demonstrated a greater reduction in pain compared to the Control group during the primary assessment at Week 8. The percent change in average pain from baseline to Week 8 was -18% (±2%) for the low-dose control and -29% (±2%) for Qutenza (capsaicin 8% patch) .

For various degrees of improvement in pain from baseline to study endpoint, Figure 2 shows the fraction of patients achieving that degree of improvement. The figure is cumulative, so that patients whose change from baseline is, for example, 50%, are also included at every level of improvement below 50%. Patients who did not complete the study through Week 12 or who showed no improvement at Week 12 were assigned 0% improvement. Some patients experienced a decrease in pain as early as Week 1, which persisted throughout the study. The proportion of patients experiencing ≥ 30% reduction in pain intensity from baseline for each week through Week 12 is shown in Figure 3.

FIGURE 2: Patients Achieving Various Percentages of Reduction in Pain Intensity at Week 12 – Study 1

Patients Achieving Various Percentages of Reduction in Pain Intensity at Week 12 – Study 1 - Illustration

FIGURE 3: Weekly Proportion of Patients Achieving ≥ 30% Pain Intensity Reduction – Study 1*

Weekly Proportion of Patients Achieving &ge; 30% Pain Intensity Reduction – Study 1 - Illustration

*The same patients may not have responded at each timepoint.

PHN Study 2: In this 12-week study the Qutenza (capsaicin 8% patch) group demonstrated a greater reduction in pain compared to the Control group during the primary assessment at Week 8. The percent change in average pain from baseline to Week 8 was -26% (±2%) for the low-dose control and -33% (±2%) for Qutenza (capsaicin 8% patch) .

For various degrees of improvement in pain from baseline to study endpoint, Figure 4 shows the fraction of patients achieving that degree of improvement. The figure is cumulative, so that patients whose change from baseline is, for example, 50%, are also included at every level of improvement below 50%. Patients who did not complete the study through Week 12 or who showed no improvement at Week 12 were assigned 0% improvement. Some patients experienced a decrease in pain as early as Week 1, which persisted throughout the study. The proportion of patients achieving ≥ 30% reduction in pain intensity from baseline for each week through Week 12 is shown in Figure 5.

FIGURE 4: Patients Achieving Various Percentages of Reduction in Pain Intensity at Week 12 – Study 2

Patients Achieving Various Percentages of Reduction in Pain Intensity at Week 12 – Study 2 - Illustration

FIGURE 5: Weekly Proportion of Patients Achieving ≥ 30% Pain Intensity Reduction – Study 2*

Weekly Proportion of Patients Achieving &ge; 30% Pain Intensity Reduction – Study 2 - Illustration

*The same patients may not have responded at each timepoint.

Last reviewed on RxList: 12/2/2009
This monograph has been modified to include the generic and brand name in many instances.

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