Anaesthetic intramuscular injection

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. 

Benzyl alcohol (see Fig. 23.20) has weak local anaesthetic properties in addition to its preservative activity and is sometimes used for that effect in preparations for intramuscular injection. However it should not be used in injections intended for children < 6 months (see Sect. 13.5.9) nor in injections intended for prematures or neonates. It also causes haemolysis in higher concentrations and dosages [3]. 

Non-physiological osmolality and pH or increased buffer concentrations in formulations can be responsible for pain at the injection site. Therefore some formulations for intramuscular use contain a local anaesthetic. Needle-free injection... 

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