Lidocaine is a local anesthetic used for numbing the skin before minor medical procedures or to alleviate pain from various conditions. While generally safe when used as directed, leaving the cream on for an extended period, particularly in higher concentrations or over a large area, can lead to the absorption of lidocaine into the bloodstream and cause severe consequences.
Systemic Risks of Prolonged Exposure
Excessive lidocaine in the bloodstream can cause local anesthetic systemic toxicity (LAST), impacting the central nervous system (CNS) and the cardiovascular system. The severity depends on the absorbed amount, exposure duration, and individual factors.
Central Nervous System (CNS) Effects
CNS symptoms often appear first. Initial, milder signs may include a metallic taste, numbness around the mouth, dizziness, tinnitus, blurred vision, confusion, or changes in temperature sensation. As blood levels rise, more severe symptoms like muscle tremors, seizures, loss of consciousness, and coma can occur.
Cardiovascular Complications
Lidocaine toxicity can seriously affect the heart, potentially leading to fatal events by disrupting electrical signals. Symptoms may include slow heart rate (bradycardia), low blood pressure (hypotension), irregular heartbeats (arrhythmias), and cardiovascular collapse, which can result in cardiac arrest.
Methemoglobinemia
Systemic lidocaine absorption can rarely cause methemoglobinemia, a blood disorder impairing oxygen transport. Infants and individuals with certain conditions like G6PD deficiency are at higher risk. Signs include bluish skin, shortness of breath, fatigue, and headache.
Factors that Increase Systemic Absorption
Several factors can increase lidocaine absorption through the skin and raise the risk of toxicity. These include using high-concentration products (above 4%), applying to a large body area, leaving the cream on for too long (beyond 30-120 minutes), applying to irritated or broken skin, and covering the area with an occlusive dressing. The FDA has warned about risks from high-strength numbing creams.
Safe vs. Unsafe Lidocaine Cream Use
Safe use of lidocaine cream is critical to avoid toxicity. The table below highlights key differences between safe and unsafe practices:
| Aspect | Safe Use | Unsafe Use |
|---|---|---|
| Concentration | Using FDA-approved products, typically 4% or less for OTC creams. | Using high-concentration creams (e.g., 5%+) without medical supervision or unapproved products. |
| Application Area | Applying to a small, specific, and intact area of skin. | Applying to large areas of the body, particularly for cosmetic purposes. |
| Application Time | Following the maximum recommended time on the packaging (often 30-120 minutes). | Leaving the cream on for multiple hours or overnight. |
| Skin Condition | Applying only to healthy, intact skin. | Applying to broken, irritated, blistered, or otherwise compromised skin. |
| Dressings | Using no dressing or a recommended, non-occlusive dressing. | Wrapping the area tightly with plastic wrap or other occlusive materials. |
| Purpose | Using for minor, temporary pain relief or specific medical procedures under guidance. | Using for unapproved conditions or attempting extensive anesthesia on your own. |
What to Do in Case of Overexposure
If you observe signs of lidocaine toxicity after prolonged exposure, take immediate action:
- Remove the Cream: Wash the affected area thoroughly with soap and water.
- Call for Help: Contact Poison Control or emergency services (911) immediately, providing details of the product and symptoms.
- Provide Information: Be ready to give details about the product, application duration, and the person's age and weight.
- Administer Treatment (if applicable): Medical treatment may include medications for seizures or lipid emulsion therapy to help clear the drug.
Conclusion: Prioritize Safety
Using lidocaine cream safely is paramount. Leaving it on too long can lead to severe, life-threatening systemic toxicity affecting the nervous system and heart. Always follow instructions, use the minimum effective amount for the shortest duration, avoid applying to damaged skin, and never use high-concentration products without medical guidance. Adhering to these guidelines ensures safe and effective use.
For additional drug safety information, consult the U.S. Food and Drug Administration's website.
