Limitations and Risk of Topical anaesthetics

Will topical anaesthetics affect pregnancy and nursing?

Dental topical anaesthetics have not shown adverse effects for developing infants and they do not show up at significant levels in breast milk. If you are pregnant or if you are nursing then you should consult your dentist for all of your concerns.

What are the limitations of topical anaesthetics?

Topical anaesthetics have certain limitations like

  • applying them across a large area could cause toxicity. It is particularly a danger for tetracaine since it is absorbed very easily
  • there are people allergic to drugs, flavourings, and certain ingredients
  • most of the topical anaesthetics have not been tested in young children, particularly those who are aged one to two
  • most of the topical anaesthetics have not yet been tested on the elderly

What are the risks when using topical anaesthetics?

The risk of using a topical anaesthetic is low but you should still keep them in mind. They are

  • allergic reactions. Even if they are usually rare and mild, sometimes they can be severe. Mild allergic reactions include swelling and raised welts on the skin that have a burning sensation and are usually itchy. Some of the allergic reactions are delayed for up to two days from the application of the anaesthetic
  • toxicity. If you receive too much anaesthesia then you may get
    • blurry vision
    • unusual nervousness or restlessness
    • dizziness
    • becoming lightheaded
    • headaches
    • ringing or buzzing in your ears
    • shivering
    • drowsiness
    • difficulty in breathing
    • seizures

Too much benzocaine causes methemoglobinemia which is a condition characterized by the inability of red blood cells to carry oxygen. Subtle forms of this condition may not produce symptoms. In severe cases, it can cause fatigue, a bluish cast, a greyish cast, and may even give you hard times breathing. It is uncommon for this to happen. It occurs in these three situations

  • in the operating room where doctors have applied excessive amounts of benzocaine or excessive amounts of tetracaine and benzocaine on the back of the throat prior to the placement of the breathing tube or special tube used to look at the stomach or the heart. Methemoglobinemia is more likely to occur in elderly patients and in debilitated patients
  • when infants are teething, some parents may disregard the manufacturer’s dosage and they may apply too much benzocaine liquid or gel inside the mouth
  • in young children who have accidentally ingested too much benzocaine

You should follow the manufacturer’s instructions for the drugs and you should keep all of the medications out of the reach of young children. For the milder cases of methemoglobinemia, you should simply observe the patient closely although in the more severe cases, methylene blue dye is injected into the vein and it will serve as an antidote.

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