Local anaesthetics Subject

Enterprise in the synthesis of new local anaesthetics shows no sign of diminution and several useful reviews dealing with the correlation of structure and local anaesthetic action have been published of which that by Moore deals generally with the subject, while Gilman, Goodman, Thomas, Hahn and Priitting discuss structure and acti-vity in... 

PROCAINE ECOTHIOPATE t plasma concentrations and risk of unconsciousness, and cardiovascular collapse with injections of prilocaine Ecothiopate inhibits pseudocholinesterase, which metabolizes prilocaine Do not co-administer. Use an alternative local anaesthetic not subject to metabolism by pseudocholinesterases... 

It is a local anaesthetic used for infiltration, peridural, nerve block, and caudal anaesthesia. It is found to be twiee as potent as procaine. It has been reported that its duration of action is significantly longer than that of lidocaine, even without adrenaline. Henee, it is of particular importance in subjects showing contraindication to adrenaline. 

It is not totally inconceivable that in predisposed subjects, local anaesthetics may cause an anaphylactoid reaction via direct conversion of the third complement in the same way as may occur with certain anaesthetic induction agents (discussed elsewhere). 

The new local anaesthetic drug aptocaine is chemically related to prilocaine, but till now no methaemoglobinaemia following its use has been reported. In a double-blind trial in 28 volunteers (35), the drug was compared at 1, 2, and 3% concentration given intradermally with lidocaine 2% and bupivacaine 0.5% whilst in 27 subjects 1% aptocaine was compared with mepivacaine and prilocaine, both 1,2 and 3%. The anaesthetic activity of aptocaine was about the same as that of mepivacaine. 

The lidocaine/cimetidine interaction is well studied but controversial. It is confused by the differences between the studies (healthy subjects, patients with different diseases, different modes of drug administration, etc). A fall in the clearance of lidoeaine (15% or more) and a resultant rise in the serum levels should be looked for if eimetidine is used, but a clinically significant alteration may not occur in every patient. It may possibly be of less importance in patients following a myocardial infarction because of the increased amounts of alpha-l-acid glycoprotein, which alters the levels of bound and free lidoeaine. Monitor all patients closely for evidence of toxicity and, where possible, check serum lidoeaine levels regularly. A reduced infusion rate may be needed. Ranitidine would appear to be a suitable alternative to eimetidine. See also Anaesthetics, local -i- H2-receptor antagonists , p.l 11. 

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