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Lidocaine is an anesthetic that works on nerve endings to reduce the sensations of pain. It is available in both a non-buffered and buffered form; the difference between them is that the buffered form contains sodium bicarbonate. This addition appears to reduce the pain of administration of the lidocaine through injection, although the exact mechanism by which buffered lidocaine does this is not yet known as of 2011. Possible explanations include a reduction in irritation at the site, additional painkilling activity, or quicker anesthetic effects.
People who may need to have lidocaine injections include those undergoing operations that only necessitate local anesthesia and those who have to have bone marrow biopsies performed. The drug acts on the nerve endings in the area of the body it is administered to, blocking the transmission of pain impulses to the brain. Commonly, lidocaine is administered through an injection, and the injection itself can be painful for the patient receiving it.
The pain of a lidocaine injection is accompanied by a sensation of burning. Scientists can assign at least part of the burning sensation to the acidic pH of lidocaine in solution. Typically, an injection product of lidocaine contains about 1% of lidocaine in 99% sterile water, producing a low pH. Once the solution gets into the body through an injection, it is thought that the acidic nature of the product irritates the tissue to produce the burning.
Buffered lidocaine has a more neutral pH than unbuffered lidocaine. This is because it contains another ingredient that is more alkaline than lidocaine called sodium bicarbonate. This chemical is the same substance that bakers add to bread as baking soda, and it is also found in some toothpastes. Commonly, the percentage of sodium bicarbonate in a buffered lidocaine product is at 8.4 percent.
Scientists know through studies of pain perception that people feel less pain with a buffered lidocaine injection than with an unbuffered injection. The safety of this method of administering lidocaine is also proven. The way that this works is not yet known in detail as of 2011, but various explanations have been put forward. Generally, they may act in conjunction with each other to produce this beneficial effect.
Irritation from low pH may be reduced inside the injection site, which provokes less pain and burning than the unbuffered version. The higher pH of a buffered lidocaine injection may actually increase the rate at which the drug gets to the nerve endings, therefore speeding up the painkilling effect. Another possible reason for the buffered drug to create less pain on injection is that the sodium bicarbonate ingredient actually produces its own painkilling effect. Carbon dioxide from the breakdown of the sodium bicarbonate could decrease the pain signals from the nerve ending, or instead help the lidocaine be more concentrated at the nerve ending.
Buffered lidocaine typically contains 0.84 percent sodium bicarbonate, not 8.4 percent.
The buffered solution has poor stability, so it is make up just before use. The usual mixture is 9 parts of lidocaine solution and 1 part of 8.4 percent sodium bicarbonate solution. 8.4 percent sodium bicarbonate solution contains one millimole or one milli-equivalent of bicarbonate per millilitre, which makes it a popular strength because of ease of calculations required for certain applications.