From the FDA Drug Label
The lowest dosage that results in effective anesthesia should be used to avoid high plasma levels and serious adverse effects. Repeated doses of lidocaine HCl may cause significant increases in blood levels with each repeated dose because of slow accumulation of the drug or its metabolites. It should be kept in mind at such times that restlessness, anxiety, tinnitus, dizziness, blurred vision, tremors, depression or drowsiness may be early warning signs of central nervous system toxicity.
The significance of accidentally injecting 2 ml of lidocaine 0.1% intramuscularly (IM) is that it may cause central nervous system toxicity or other adverse effects. The FDA drug label recommends using the lowest dosage that results in effective anesthesia to avoid high plasma levels and serious adverse effects. However, the label does not provide a specific dosage limit for a single accidental injection.
- Key considerations:
- Dose and concentration: The actual volume and concentration used depend on factors like the type and extent of the procedure, depth of anesthesia, and patient condition.
- Patient condition: Dosages should be reduced for children, the elderly, debilitated patients, and those with cardiac and/or liver disease.
- Monitoring: Careful and constant monitoring of cardiovascular and respiratory vital signs and the patient's state of consciousness is necessary after each local anesthetic injection. 1 1 1
From the Research
Accidental intramuscular injection of 2 ml of lidocaine 0.1% is generally not clinically significant. This dose contains only 2 mg of lidocaine (0.1% means 1 mg/ml), which is well below the toxic threshold, as noted in a case report on local anesthetic systemic toxicity 2. For context, therapeutic doses of lidocaine for local anesthesia typically range from 20-200 mg, and toxicity usually occurs at much higher doses (>300 mg in adults) 3. The small amount injected would be absorbed gradually from muscle tissue and metabolized by the liver without causing systemic effects. Patients may experience mild local effects like temporary numbness or discomfort at the injection site. However, if the patient shows any unusual symptoms such as dizziness, ringing in the ears, metallic taste, confusion, or cardiac arrhythmias (which would be extremely unlikely at this dose), medical attention should be sought. Individuals with severe liver disease or certain cardiac conditions might be more sensitive to even small amounts of lidocaine, but this dose remains minimal for almost all patients.
Some key points to consider in the use of local anesthetics include the potential for local anesthetic systemic toxicity (LAST), which can affect the cardiac and central nervous systems, and the importance of healthcare providers being trained in LAST treatment and prevention 2. Additionally, the dosage of local anesthetics should be adjusted in certain populations, such as children, elderly, and fragile individuals, and those with organ failures, as their metabolism of the compounds may be impaired 3.
In terms of management, intravenous lipid emulsion is an important life-saving treatment in severe, life-threatening cases of LAST 3. It is also essential to recognize the signs and symptoms of LAST, which can range from mild findings, such as temporary hypertensive events, to serious conditions, including refractory cardiac dysfunction, dysrhythmias, and prearrest situations 3.
Overall, while accidental intramuscular injection of 2 ml of lidocaine 0.1% is not expected to cause significant harm, it is crucial to be aware of the potential risks and take steps to prevent and manage any adverse effects that may occur.