Dr. James WyrickEmergency Medicine

Why Do Local Anesthetics Cause Pain?

1 min read
Local anesthetics such as lidocaine and bupivacaine are commonly used in many surgical and dental procedures. So why do they cause pain when injected?
First there is the pain from the needle. Sometimes things can be done to decrease the pain of the needle piercing the site of injection.
Another factor is the temperature of the medication. It is stored at room temperature instead of body temperature so this can increase the pain of injection somewhat.
However, a major factor is the pH of the medication. The normal pH of the human body is around 7.4. The pH of local anesthetics ranges from about 3.9 to 6.5 depending on the specific medicine.
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Since the anesthetic is acidic compared to the human body this causes pain with injection.
Fortunately most local anesthetics work very quickly so the pain from injection does not last very long.
It’s definitely better to have some brief pain from the anesthetic than having a procedure done with out it.