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To the Editor:—
Harvey Bernard, MD, (208:1196, 1969), advised preparing the skin for lumbar puncture with a hexachlorophene-containing soap followed by benzalkonium chloride. James A. Visconti, PhD, and Donald Schneider RPh; then wrote you (209:2057, 1969) pointing out, quite properly, that soaps are anionic and consequently incompatible with cationic detergents such as benzalkonium chloride. They therefore advised removing the soap by thorough rinsing with water before applying the germicide.However, it is almost impossible to remove all soap with water. Water and soap constitute a colloidal suspension; if you rub the skin after what you consider a complete removal of soap with water, you can usually stir up a few more suds, sufficient to inactivate the cationic germicide. Alcohol and soap, on the other hand, are 100% soluble in one another. If you, therefore, expect a quaternary ammonium antiseptic to act effectively after preliminary preparation with soap, 70%
Kahn S. Preparation of Skin for Lumbar Puncture. JAMA. 1969;210(10):1923. doi:10.1001/jama.1969.03160360069024