Benzocaine is a local anaesthetic agent belonging to the ester group and it is one of the key pharmacological ingredients used in oral gels. This is used to treat mouth and gum pain or teething problems due to its local anaesthetic property. Even though it is commonly prescribed in dentistry, it should be used with caution especially in children. This is because; benzocaine is known to cause acute toxic methemoglobinemia, a rare but fatal condition.
Methemoglobinemia is a blood disorder where it causes reduced oxygen-carrying capacity of the red blood cells to the various tissues of the body. Methemoglobin is formed when the iron in the ferrous form is converted to ferric form and this compound is unable to bind and carry oxygen to the various tissues of the body leading to functional anaemia. Methemoglobinemia can be congenital or acquired. Benzocaine-induced methemoglobinemia is an example of acquired form. 15-25mg benzocaine/kg body weight can cause Methemoglobinemia. This is observed in the children aged below 2years.
The signs of benzocaine-induced methemoglobinemia can be seen soon or few hours’ after its application. One of the early features is cyanosis. This may be followed by anxiety, fatigue, dyspnoea, tachycardia, headache and syncope. Death is a terminal stage of this abnormal haemoglobin. All these clinical features depend on the percentage of the methemoglobin. Any patient observed with any of the above mentioned clinical features should seek immediate medical management, failing which the results may be fatal. So, one need to be cautious in prescribing the benzocaine based oral gel for the children and if so prescribed, warn the caretakers about the possible side effects.