• A simple, sensitive, and specific radioreceptor assay has been developed for the measurement of anticholinergic drugs in human serum. The assay is based on the competitive inhibition by free anticholinergic drugs in a 0.2-mL sample of serum with the specific binding of the potent muscarinic antagonists, tritiated quinuclidinyl benzilate, to solubilized brain muscarinic receptors. Anticholinergic activity could be detected regardless of drug structure and was quantified against atropine standards. Although the serum levels of anticholinergic drugs varied considerably in 35 patients receiving both neuroleptic and anticholinergic drugs, there was a highly significant inverse correlation between the presence of acute extrapyramidal side effects due to neuroleptics and the serum levels of anticholinergics.
Tune L, Coyle JT. Serum Levels of Anticholinergic Drugs in Treatment of Acute Extrapyramidal Side Effects. Arch Gen Psychiatry. 1980;37(3):293-297. doi:10.1001/archpsyc.1980.01780160063007