A capsaicin patch is a topical medication applied to the skin for pain relief, and is often prescribed for patients suffering from nerve pain due to postherpetic neuralgia, or shingles. This drug is a TRVP1 channel agonist, which means that it works by interfering with the nociceptors, or sensory receptors located at nerve endings. The active ingredient in the patch, capsaicin, binds to these receptors to prevent them from sending pain signals to the brain.
Often, a doctor or nurse will apply the capsaicin patch, or the patient may be shown how to use it at home. Patients must wear gloves when applying the patch to the skin to prevent the medicine from making contact with any other part of the body. Once the patch is applied to the area of skin being treated, patients must refrain from touching it with their bare hands. The capsaicin patch may be removed after 30 to 60 minutes and patients may use this medicine again every 90 days, as needed. It may take up to two weeks for the full effect of the drug to be noticed.
A capsaicin patch is not intended for use on a person's face or scalp and it should never make contact with the nose, mouth, or eyes. Inhalation of the drug can occur, which may result in coughing, shortness of breath, and sneezing. Patients may notice that the treated skin is more sensitive to heat for several days following the treatment. The capsaicin patch should never be applied to skin that is broken or otherwise damaged.
Some mild side effects may occur while using capsaicin patches, which should be reported to the prescribing physician if they become bothersome or do not go away. Patients may experience nausea, a sore throat, and mild pain. They may notice some redness at the area of skin where the patch is applied, as well as itchiness and a burning sensation. Some people using the capsaicin patch have reported drying of the skin, swelling, or blisters.
More serious side effects should be reported to the doctor as soon as possible, and may require medical care. Some people experience an increase in blood pressure while wearing the patch, which may also be accompanied by heart palpitations and an increased heart rate. Those who undergo treatment under a doctor's supervision will likely be monitored for blood pressure increases. Other serious side effects may include shortness of breath, severe dizziness, and severe pain, as well as symptoms of an allergic reaction, such as tightness in the chest, hives, and swelling of the facial area. Rarely, some patients have reported changes in taste, muscle spasms, and first degree atrioventricular block, which means that the electrical impulses in the heart transfer more slowly.
People with certain medical conditions may be unable to use the capsaicin patch. These can include those with diabetes, uncontrolled hypertension, and a history of heart problems. It is not intended for use by people under the age of 18. As of 2011, the safety of this drug when used by women who are pregnant or breastfeeding has not been established.