Anesthetic benzocaine carries risk of blood condition

Canadians facing surgical, dental or other medical procedures should know that the local anesthetic benzocaine has been linked to a potentially serious blood condition, Health Canada said Friday.

The blood condition methemoglobinemia is an uncommon side-effect linked to the topical anesthetic, which is used to numb the skin, inside of the nose or lips. Benzocaine is available in varying strengths as a gel, cream, liquid or spray.

Methemoglobinemia reduces the ability of red blood cells to deliver oxygen, which can lead to bluish discolouration of the skin, nausea and fatigue that can progress to stupor, coma and death.

Health Canada has received reports of nine suspected cases of the condition linked to the use of benzocaine. None of them were fatal.

In most of the reported cases, health professionals used high-concentration sprays containing 14 to 20 per cent benzocaine to numb mucous membranes during medical procedures.

Risk factors

Infants may be at increased risk of the condition, as well as those who:

• Have pre-existing inflammation or damage to the mucous membranes where the benzocaine is applied.
• Have heart disease.
• Suffer from malnutrition.
• Have certain metabolic conditions such as a deficiency in the enzyme glucose-6-phosphate dehydrogenase or hemoglobin reductase.

Cases continue to be reported to the department and more are appearing in the medical literature, Health Canada said in its notice to hospitals.

Health professionals should record how many sprays are given and the length of each spray, using the minimum amount needed.

Patients should be monitored for signs and symptoms of methemoglobinemia, and suspected cases should be confirmed by measuring levels of methemoglobin in the blood, the notice said.