Lidocaine (also known as Lignocaine and Xylocaine) and Lidocaine Hydrochloride have been used since 1948 for medical applications such as surface pain and itch reduction among other uses. Lidocaine has a fairly low toxicity as the LD50 for the hydrochloride is approx. 459 mg/kg of body weight.
Lidocaine, commonly referred to as the “base” molecule is not soluble in water. It is soluble in alcohol or hydrocarbons. The hydrochloride or “salt” form is freely soluble in water. This is an important fact to be considered when developing a topical cream or ointment using these as an ingredient. Lidocaine and its hydrochloride are not to be used for any type of oral products, as swallowing could be harmful. The maximum concentration allowed by the FDA in a Lidocaine Topical product is 5%.
Lidocaine works by blocking Sodium Channels in the neuronal cell membrane. Although rare, Toxicity can result from high blood concentrations in individuals who have certain risk factors. This is the reason why it is important when developing a topical skin product with Lidocaine there must be FDA approval before the product goes to market. This is also the reason it is NOT to be used in any type of oral product or any application where it could be swallowed. If used properly, Lidocaine continues to be a very useful ingredient in topical skin itch and numbing products around the world.