Canadian Journal of Anesthesia, Vol 19, 75-82, Copyright © 1972 by Canadian Anesthesiologists' Society

The Effect of a Series of Anti-Cancer Drugs on Plasma Cholinesterase Activity

¹ University of Michigan Medical Center, Department of Anesthesiology, Ann Arbor, Michigan, USA and Anesthesia Research Laboratory of Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

Prolonged apnoea caused by succinylcholine in combination with anti-cancer drugs in patients suffering from maligant tumors has been reported in past.

In order to determine the potential inhibitory effect of anti-cancer agents on plasma cholinesterase in vivo in cancer patients, a systematic study was carried out to determine there in vitro inhibitory effect. Utilizing Kalow's ultraviolet spectrophotometric method the hydrloysis of benzoylcholine and procaine by purified human cholinesterase and pooled human plasma was determined both in the presence and in the absence of anti-cancer agents. Of those studied, only the alkylating agents possess significant anticholinesterase effects. These are in decreashing order of effectivness: triethylene-melamine (TEM), cyclophosphamide (Cytoxan), mechlorethamine (Nitrogen Mustard) and triethylene thiophosphoramide (Thio-tepa). The corresponding I₅₀ values are 3.3 x 10^-4 M, 4.0 x 10^-4 M, 6.3 x 10^-4 M, 7.9 x 10^-4 M, concentrations with benzoylcholine as the substrate. In patients and especially in those treated with large intravenous doses of these anti-cancer drugs, the dose of succinylcholine should be reduced in proportion to the reduction of plasma cholinestrase activity to prevent prolonged apnoea and cardiac arrythimas which even may result in arrest. Therefore, patients who have more than 70 per cent reduction in plasma chplinesterase activity should be protected by wearing an Identification Tag.