[Famotidine does not modify the plasma levels of lidocaine for spinal anesthesia. A comparative study of famotidine and cimetidine].

H2 receptor antagonists are often used to reduce gastric acidity prior to general or regional anaesthesias. However cimetidine and ranitidine have been found to increase plasma levels of local anaesthetics such as lidocaine. This study aimed to compare famotidine--another H2 receptor antagonist--with cimetidine in this respect. 33 male patients 70 years old or more, scheduled for surgery under spinal anaesthesia and randomized into 3 groups, received either diazepam 0.15 mg.kg-1 and famotidine 20 mg (group A) or diazepam and cimetidine 200 mg (group B) or diazepam only (group C) on the previous night and 90 minutes before spinal anaesthesia by hyperbaric lidocaine 5%, 3 ml. Arterial blood samples were taken 3 minutes after spinal injection then every 15 minutes unto 90 minutes after the first sampling. Lidocaine plasma levels were measured by fluorescence polarization immunoassay and the results were statistically analyzed. In famotidine group lidocaine levels were intermediate between B and C groups levels, and the increase was of lesser duration than in B group. Elimination mechanism of lidocaine with and without H2 inhibitor is briefly discussed. Therefore famotidine would appear to be more convenient than other H2 receptor inhibitors whenever antacid protective effects are sought after prior to regional anaesthesia.