<p>In common with other local anaesthetics, adverse reactions to lidocaine are rare and are usually the result of excessively high blood concentrations due to inadvertent intravascular injection, excessive dosage, rapid absorption or occasionally to hypersensitivity, idiosyncracy or diminished tolerance on the part of the patient. In such circumstances systemic effects occur involving the central nervous system and/or the cardiovascular system. CNS reactions are excitatory and/or depressant and may be characterized by nervousness, dizziness, blurred vision and tremors, followed by drowsiness, convulsions, unconsciousness and possibly respiratory arrest. Cardiovascular reactions are hypotension, myocardial depression, bradycardia and possibly cardiac arrest. Allergic reactions are extremely rare. They may be characterized by cutaneous lesions, urticaria, oedema or anaphylactoid reactions.</p>