From the Guidelines
A metallic taste in the mouth is a common early symptom of lidocaine toxicity, which requires immediate attention. If you experience a metallic taste while receiving lidocaine, inform your healthcare provider immediately as this may indicate that blood levels are approaching toxic range. Other early symptoms to watch for include numbness around the mouth, lightheadedness, dizziness, visual disturbances, and ringing in the ears. Lidocaine toxicity occurs when the medication reaches excessive levels in the bloodstream, typically above 5 μg/mL, and can progress to more serious effects including seizures, cardiac arrhythmias, and even cardiovascular collapse if not addressed. This toxicity is more likely with rapid intravenous administration, accidental intravascular injection during local anesthesia, or when using high doses, especially in patients with liver dysfunction since the liver metabolizes lidocaine. Treatment involves stopping lidocaine administration immediately, providing supportive care, and in severe cases, administering benzodiazepines for seizures or appropriate cardiac support. The metallic taste occurs because lidocaine affects taste receptors and sensory nerves in the mouth, altering taste perception as blood levels rise, as reported in a study published in the journal Anaesthesia 1.
Some key factors that may influence lidocaine toxicity include:
- Acid-base status, with acidaemia increasing the dissociation of lidocaine from plasma proteins 1
- Hypoalbuminaemia and other conditions where plasma proteins are depleted, increasing the amount of free drug in the plasma and making toxicity more likely 1
- Drugs that reduce lidocaine metabolism, such as beta-blockers, and clearance, such as amiodarone, which may enhance lidocaine toxicity, especially with prolonged infusions 1
- Low body weight, which can result in a reduction in skeletal muscle mass and may be associated with an increased frequency of adverse reactions 1
It is essential to monitor patients receiving intravenous lidocaine closely, especially in the presence of these risk factors, and to be aware of the signs and symptoms of toxicity, including metallic taste, to ensure prompt intervention and prevent serious complications, as emphasized in the international consensus statement on efficacy and safety of intravenous lidocaine for postoperative pain and recovery 1.
From the Research
Lidocaine Toxicity Symptoms
- The symptoms of lidocaine toxicity include numbness of the tongue, dizziness, tinnitus, visual disturbances, muscle spasms, convulsions, coma, and respiratory and cardiac arrest 2
- Metallic taste is not mentioned as a symptom of lidocaine toxicity in the provided studies
Treatment of Lidocaine Toxicity
- Lipid emulsion therapy has been shown to be effective in treating lidocaine toxicity 2, 3, 4, 5
- The mechanism of action of lipid emulsion therapy is not well defined, but it has been postulated to work by both a "lipid sink" and a direct "energy source" to the myocardium 5