Could lidocaine be causing the intermittent psychiatric symptoms and tachycardia in a patient on a three‑drug psychotropic regimen?

Lidocaine is Unlikely to Be Causing the Psychiatric Symptoms and Tachycardia

Lidocaine does not cause tachycardia—it is a sodium channel blocker that typically slows heart rate and conduction, not accelerates it. The psychiatric symptoms could theoretically be lidocaine-induced if the patient is receiving therapeutic doses, but tachycardia points away from lidocaine toxicity and toward other causes in the psychotropic regimen or an underlying medical condition 1, 2, 3.

Lidocaine's Cardiovascular Effects

Expected Cardiac Effects

• Lidocaine acts as a Class Ib antiarrhythmic that blocks voltage-dependent sodium channels, which decreases automaticity, slows conduction, and typically does not increase heart rate 4.
• The drug depresses cardiac conduction and contractility rather than stimulating heart rate, similar to other Class I antiarrhythmic agents 2.
• In clinical studies, lidocaine administration during ventricular tachycardia actually increased tachycardia cycle length (slowed the rate) rather than accelerating it 5.
• Lidocaine is specifically used to treat ventricular tachyarrhythmias, not cause them 6, 7, 4.

Cardiovascular Toxicity Profile

• When lidocaine toxicity does affect the cardiovascular system, it manifests as myocardial depression, hypotension, bradycardia, and circulatory depression—not tachycardia 6, 3.
• High concentrations may cause complete heart block and wide complex tachycardia, but these are conduction disturbances, not primary increases in heart rate 6.

Lidocaine's Neuropsychiatric Effects

Well-Documented CNS Toxicity

• Neuropsychiatric side effects from lidocaine are extremely common and well-recognized, occurring in 1.8-100% of patients in published series, with one study documenting psychiatric symptoms in 75% of headache patients treated with lidocaine 8.
• Early CNS toxicity appears at plasma levels >6 μg/mL and includes perioral numbness, dizziness, confusion, slurred speech, restlessness, anxiety, tinnitus, blurred vision, tremors, and drowsiness 1, 3.
• More severe toxicity progresses to seizures, respiratory depression, and cardiovascular collapse 1, 3.
• The psychiatric presentation is stereotypical and consistent across different patient populations, ages, and dosages 8.

Risk Factors for Toxicity

• Elderly patients (>70 years), those with hepatic dysfunction, congestive heart failure, or cardiogenic shock are at higher risk due to reduced clearance 1, 3.
• Repeated doses cause accumulation because of slow drug metabolism 3.

Clinical Reasoning Algorithm

Step 1: Assess for Lidocaine Exposure

• Is the patient actually receiving lidocaine? Check for IV infusions, topical applications, or recent procedures involving local anesthesia 3.
• If no lidocaine exposure exists, it cannot be the cause.

Step 2: Evaluate the Tachycardia

• Tachycardia argues strongly against lidocaine as the primary culprit 2, 5, 4.
• Consider alternative causes:
  • Anticholinergic effects from psychotropic medications
  • Serotonin syndrome from drug interactions
  • Sympathomimetic effects from certain antidepressants or antipsychotics
  • Withdrawal states
  • Underlying medical conditions (hyperthyroidism, infection, dehydration)

Step 3: Evaluate the Psychiatric Symptoms

• If lidocaine exposure is confirmed, assess for classic CNS toxicity symptoms: confusion, perioral numbness, tinnitus, visual changes, tremors 1, 3, 8.
• Check serum lidocaine levels if prolonged or high-dose infusion, or if neurologic changes are present 1.
• Consider that psychiatric symptoms may be intermittent if related to fluctuating drug levels or interactions with the psychotropic regimen 8.

Step 4: Consider Drug Interactions

• Psychotropic medications that affect hepatic metabolism (CYP450 system) could theoretically increase lidocaine levels if both are being administered 3.
• However, this would not explain isolated tachycardia without other signs of lidocaine toxicity.

Critical Pitfalls to Avoid

• Do not attribute tachycardia to lidocaine toxicity—this is inconsistent with the drug's pharmacology and would require looking elsewhere for the cause 2, 5, 4.
• Do not overlook serotonin syndrome or anticholinergic toxicity from the psychotropic regimen, which commonly presents with both psychiatric symptoms AND tachycardia.
• Do not miss lidocaine-induced seizures, which can occur with severe toxicity and may be mistaken for psychiatric agitation 1, 3.
• If lidocaine toxicity is suspected based on CNS symptoms, measure serum levels and discontinue or reduce the infusion immediately 1.

Most Likely Alternative Explanations

The combination of psychiatric symptoms and tachycardia in a patient on a three-drug psychotropic regimen is far more consistent with:

• Drug-drug interactions within the psychotropic regimen
• Serotonin syndrome (confusion, agitation, tachycardia, hyperthermia)
• Anticholinergic toxicity (confusion, tachycardia, dry mucous membranes, urinary retention)
• Neuroleptic malignant syndrome
• Underlying medical illness (sepsis, thyrotoxicosis, substance withdrawal)