Lidocaine patches are a form of topical anesthetic delivery designed to provide localized pain relief. They contain lidocaine, an amide-type local anesthetic that stabilizes neuronal membranes, inhibiting the conduction of pain impulses. Prescription-strength patches are primarily used to manage post-herpetic neuralgia, which is persistent nerve pain following a shingles infection. The controlled release mechanism allows the medication to act locally, minimizing the amount of drug that enters the bloodstream compared to oral medications.
Common Skin Reactions at the Application Site
The most frequently reported adverse effects from using lidocaine patches are confined to the area of skin where the patch is placed. These application site reactions are typically mild and transient, often resolving on their own within a few minutes or hours after the patch is removed. Common reactions include temporary redness (erythema) and mild swelling (edema). Users may also experience a sensation of burning or itching (pruritus) directly under the patch. Localized skin irritation can also manifest as blisters, bruising, or the development of small bumps (papules or vesicles). These reactions are usually a response to either the adhesive material or the lidocaine itself, and they can often be managed by rotating the exact spot of application.
Recognizing Signs of Systemic Toxicity
Although lidocaine patches are designed for local action, systemic toxicity can occur if too much of the drug is absorbed into the bloodstream. This is more likely if the patch is applied improperly, such as to damaged skin, or if an excessive number of patches are used. Signs of systemic toxicity primarily involve the central nervous system (CNS) and the cardiovascular system. Initial CNS symptoms may include lightheadedness, dizziness, or a metallic taste in the mouth. Users might also notice ringing in the ears (tinnitus), confusion, or slurred speech. As the lidocaine concentration in the blood increases, these symptoms can progress to neurological effects like muscle twitching, convulsions, drowsiness, or loss of consciousness. Cardiovascular effects occur at higher systemic concentrations. Symptoms include changes in heart rate (slow or fast pulse) and low blood pressure (hypotension). Severe toxicity can lead to shortness of breath, irregular heart rhythms, or cardiac arrest. Immediate medical attention is required if serious signs, such as difficulty breathing or an irregular heartbeat, are observed.
Mitigation Strategies and Safe Patch Application
Preventing both local and systemic adverse effects depends heavily on strictly following the recommended application instructions. To minimize the risk of increased systemic absorption, it is advised to apply the patch only to clean, dry, and intact skin. Applying the patch to broken, irritated, or inflamed skin, such as a cut or rash, can significantly increase the amount of lidocaine absorbed into the body.
Users must adhere strictly to the maximum wear time. For prescription patches, this is typically 12 hours within a 24-hour period, followed by a 12-hour patch-free interval. Using more than the prescribed number of patches or wearing them for longer than recommended increases the risk of high blood concentrations and serious side effects.
It is also important to avoid external heat sources, such as heating pads or electric blankets, over the patch area, as heat can accelerate the absorption of lidocaine into the body. Proper disposal is a final safety measure to prevent accidental exposure, especially to children and pets.
After removing a used patch, it should be folded in half with the adhesive sides stuck together to prevent any remaining medication from being accessible. The folded patch should then be discarded immediately in a container that is inaccessible to others.