Lidocaine intramuscular injection

Parenteral 1 g powder to reconstitute for intravenous (0.9% NaCl diluent) or intramuscular (1% lidocaine diluent) injection... 

Because lidocaine undergoes nearly complete first-pass hepatic metabolism by CyP 3 A4 and 2D6 when administered orally, it is administered only as an intravenous or intramuscular injection. Once in the blood, it is 50% bound to protein, mainly to AAG and albumin. Clearance of lidocaine is very rapid. The distribution half-life is -0.5 hour, and the elimination half-life is 1 to 1.5 hours. Reduced hepatic function impairs clearance and causes prolonged elimination and accumulation of the drug. This is due both to reduced blood flow to the liver (seen in heart failure) and to decreased metabofism of lidocaine. The end effect is lidocaine intoxication if the dose is not adjusted to account for this decreased metabolic rate. 

C. Local pain may occur at intramuscular injection sites. Lidooaine (1 mL of 1% lidocaine per mL of EDTA concentrate) may be added to intramuscular injections to decrease discomfort. 

Twenty patients undergoing surgery were given repeated 1-mg intravenous doses of midazolam as induction anaesthesia every 30 seconds until they failed to respond to three repeated commands to squeeze the anaesthetist s hand. This was considered as the induction end-point titrated dose. It was found that the 10 who had been given prior spinal anaesthesia with tetracaine 12 mg needed only half the dose of midazolam (7.6 mg) than the 10 other patients who had not received tetracaine (14.7 mg). The reasons are not known. The authors of this report simply advise care in this situation. In another study in which patients were given intravenous midazolam following an intramuscular injection of either bupivacaine, lidocaine or saline, it was found that both anaesthetics enhanced the effect of midazolam. This effect was dose-dependent and it was concluded that the use of lidocaine or bupivacaine for regional blocks or local infiltration could alter the effect of midazolam from sedative to hypnotic. ... 

Parenteral administration can be associated with pain at the injection site. The so-called injection fear may be diminished by applying topically anaesthetics prior to injection. Eutectic mixtures of local anaesthetics (e.g. lidocaine/ prilocaine cream or a tetracaine gel) have proven to be effective and well-tolerated in the relief of pain associated with intramuscular injections, venepuncture or intravenous injection in adults and children. 

Schwartz, M.L., Meyer, M.B., Covino, B.G. and Narang, R.M. (1974). Antiarrhythmic effectiveness of intramuscular lidocaine Influence of different injection sites. J. Clin. Pharmacol. 14 77-83. 

Intramuscular (i.m.) injections are an alternative when i.v. access is not available. For example, lidocaine has been shown to be rapidly absorbed after i.m. injection, with the deltoid muscle being a superior site to either the buttocks or lateral thigh. Many drugs show great variability in absorption after intramuscular or subcutaneous injection. Because of the uncertainty in the bioavailability of the drug from these routes, in an emergency the i.v. route is clearly superior for rapid administration of a defined dose. 

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