Lidocaine is a widely used local anesthetic medication designed to temporarily create a numbing sensation in a specific area of the body. As a topical analgesic, it is a common ingredient in creams, gels, and patches applied directly to the skin to manage localized discomfort. The primary goal of this medication is to interrupt the transmission of pain signals before they reach the brain. This article examines the effectiveness of lidocaine for various back pain conditions, explains the mechanism by which it achieves nerve blockade, and outlines safety considerations for its proper use.
Effectiveness for Different Back Pain Conditions
The ability of lidocaine to relieve back pain depends on the pain source and the method of drug delivery. Topical lidocaine patches, available in prescription-strength (5%) and over-the-counter (4%) formulations, are best suited for pain originating near the skin’s surface. This includes localized musculoskeletal discomfort or peripheral neuropathic pain, such as the nerve pain following a shingles outbreak, which is the only condition for which the 5% patch is specifically approved by the FDA.
Patches diffuse medication into the tissue layers beneath the application site, targeting nerve endings in the skin and superficial muscles. They are less effective for deep-seated, systemic back pain originating from structures like vertebral discs, ligaments, or facet joints. Since topical lidocaine does not treat inflammation, it will not resolve pain caused primarily by an inflammatory process.
For more severe or centralized pain, a physician often administers lidocaine through injection. It is commonly used in nerve block procedures, trigger point injections, and epidural injections near the spinal cord. The medication is delivered directly to the involved nerve or muscle group, providing immediate, short-lived relief lasting only a few hours. These injections can also serve a diagnostic purpose, confirming the precise source of the patient’s pain.
How Lidocaine Blocks Pain Signals
Lidocaine interferes with nerve impulse transmission, the electrical signal that carries pain sensation. Pain signals travel along nerve cells, or neurons, as an electrical event called an action potential. This event is initiated by the rapid movement of ions across the nerve cell membrane.
The medication blocks voltage-gated sodium channels embedded within the nerve cell membrane. These channels are pores that must open to allow positively charged sodium ions to rush into the neuron. This influx of sodium causes the change in electrical charge, or depolarization, that propagates the pain signal down the nerve fiber.
Lidocaine molecules bind to the inner side of these sodium channels, preventing them from opening and blocking the flow of sodium ions. By inhibiting this movement, the drug prevents the nerve cell from transmitting the electrical impulse. This temporary blockade results in the numbing sensation and elimination of pain perception. The effect is reversible; once the medication is metabolized, the nerve’s normal function returns.
Safety Considerations and Proper Use
Topical lidocaine is generally safe when used as directed, but improper application can lead to health risks due to excessive absorption into the bloodstream. Local side effects are common and mild, including temporary skin irritation, redness, a mild burning sensation, or a rash at the application site.
A serious concern is Local Anesthetic Systemic Toxicity (LAST), which occurs when too much lidocaine is absorbed into the circulatory system. This can happen from applying too many patches, wearing them too long, or using them on damaged or irritated skin. Applying heat to the area also increases the rate of absorption.
Early symptoms of systemic toxicity often involve the central nervous system. These can include:
- Dizziness or lightheadedness
- A metallic taste in the mouth
- Confusion
- Numbness around the lips and tongue
As concentration increases, symptoms may progress to muscle twitching, slurred speech, seizures, and severe cardiovascular effects like low blood pressure. To use topical lidocaine safely, never apply it to open wounds, and strictly follow the recommended wear time (e.g., 12 hours on/12 hours off for the prescription patch). Individuals with pre-existing heart conditions or severe liver impairment should consult a physician.