Adverse experiences following the administration of lidocaine are similar in nature to those observed with other amide local anesthetic agents. These adverse experiences are, in general, dose-related and may result from high plasma levels caused by overdosage, rapid absorption, or inadvertent intravascular injection, or may result from a hypersensitivity, idiosyncrasy or diminished tolerance on the part of the patient.

Table 1: Adverse Drug Reaction Frequencies

Serious adverse experiences are generally systemic in nature. The following types are those most commonly reported:

Central Nervous System

CNS manifestations are excitatory and/or depressant and may be characterized by circumoral paresthesia, lightheadedness, nervousness, apprehension, euphoria, confusion, dizziness, drowsiness, hyperacusis, tinnitus, blurred vision, vomiting, sensations of heat, cold or numbness, twitching, tremors, convulsions, unconsciousness, respiratory depression and arrest. The excitatory manifestations may be very brief or may not occur at all, in which case the first manifestation of toxicity may be drowsiness merging into unconsciousness and respiratory arrest.

Drowsiness following the administration of lidocaine is usually an early sign of a high lidocaine plasma level and may occur as a consequence of rapid absorption.

Cardiovascular System

Cardiovascular manifestations are usually depressant and are characterized by bradycardia, hypotension, arrhythmia, and cardiovascular collapse, which may lead to cardiac arrest.

Allergic

Allergic reactions are characterized by cutaneous lesions, urticaria, edema or, in the most severe instances, anaphylactic shock. Allergic reactions of the amide type are rare and may occur as a result of sensitivity either to the local anesthetic agent or to other components in the formulation.

Neurologic

The incidences of adverse reactions may be related to the total dose of local anesthetic administered but is also dependent upon the particular drug used, the route of administration and the physical status of the patient. Neuropathy and spinal cord dysfunction (e.g. anterior spinal artery syndrome, arachnoiditis, cauda equina syndrome), have been associated with regional anesthesia. Neurological effects may be related to local anesthetic techniques, with or without a contribution from the drug.

In the practice of lumbar epidural block, occasional unintentional penetration of the subarachnoid space by the catheter or needle may occur. For example, a high spinal is characterized by paralysis of the legs, loss of consciousness, respiratory paralysis and bradycardia.

Neurologic effects following unintentional subarachnoid administration during epidural anesthesia may include spinal block by varying magnitude (including total or high spinal block), hypotension secondary to spinal block, urinary retention, fecal and urinary incontinence, loss of perineal sensation and sexual function, persistent anesthesia, paresthesia, weakness, paralysis of the lower extremities and loss of sphincter control, all of which may have slow, incomplete or no recovery; headache, backache, septic meningitis, meningismus, slowing of labour, increased incidence of forceps delivery, or cranial nerve palsies due to traction on nerves from loss of cerebrospinal fluid.

Preclinical safety data

In animal studies, the signs and symptoms of toxicity noted after high doses of lidocaine are the results of the effects on the central nervous and cardiovascular systems. No drug related adverse effects were seen in the reproduction toxicity studies, neither did lidocaine show any mutagenic potential in either in vitro or in vivo mutagenicity tests. Cancer studies have not been performed with lidocaine, due to the area and duration of therapeutic use for this drug.

Lidocaine should be used with caution in patients receiving other local anesthetics or agents structurally related to amide-type local anesthetics (e.g. certain anti-arrhythmics, such as mexilitine) since the toxic effects are additive. Specific interaction studies with lidocaine and anti-arrhythmic drugs class III (e.g. amiodarone) have not been performed, but caution is advised.

XYLOCAINE with Epinephrine or other vasopressors should not be used concomitantly with ergot-type oxytocic drugs, because a severe persistent hypertension may occur and cerebrovascular and cardiac accidents are possible. Likewise, XYLOCAINE with Epinephrine or solutions containing XYLOCAINE and another vasoconstrictor should be used with extreme caution in patients receiving monoamine oxidase inhibitors (MAO) or antidepressants of the triptyline or imipramine types, because severe prolonged hypertension may result. In situations when concurrent therapy is necessary, careful patient monitoring is essential. Phenothiazines and butyrophenones may oppose the vasoconstrictor effects of epinephrine giving rise to hypotensive responses and tachycardia.

If sedatives are employed to reduce patient apprehension, they should be used in reduced doses, since local anesthetic agents, like sedatives, are central nervous system depressants which in combination may have an additive effect.

Solutions containing epinephrine should be used with caution in patients undergoing general anesthesia with inhalation agents such as halothane and enflurane, due to the risk of serious cardiac arrhythmias.

Non-cardioselective betablockers such as propranolol enhance the pressor effects of epinephrine, which may lead to severe hypertension and bradycardia.

Drug/Laboratory Test Interactions

The intramuscular injection of lidocaine may result in an increase in creatine phosphokinase levels. Thus, the use of this enzyme determination, without isoenzyme separation, as a diagnostic test for the presence of acute myocardial infarction may be compromised by the intramuscular injection of lidocaine.

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