Pharmaceutical Studies on Certain Lidocaine Formulations

Lidocaine (LD), the most commonly used of amide-linked local anesthetic , is usually the drug of choice for the emergency treatment of ventricular arrythmia and for prophylaxis after myocardial infarction . However, some pharmaceutical problems correlated to LD preparations, such as , LD cannot be given orally , due to its extensive first-pass metabolism in the liver. its bioavailability is only about one third of the drug that reaches the general circulation after oral administration . Large dose is needed to compensate the efect of first-pass metabolism, but it produces a high concentration of toxic metabolites. Also LD is restricted , to be given by I.V route due to its short elimination half life, which is approximately 1.5 hrs.This means that an I.V. infusion for longer than few hours is required to keep the plasma concentration within the therapeutic range. LD, in the salt form , cannot penetrate the skin easily, but its corresponding un-ionzed base can penetrate the skin to a greater extent .As reported , the local anesthetic activity usually increases by increasing the concentration of the un-ionzind form of the drug.