The Chew 2008 study: what 107-drug anticholinergic activity testing actually measured

Abstract

Chew and colleagues’ 2008 study is frequently cited in discussions of anticholinergic medication evidence, but its measurement should not be confused with a universal clinical burden score. This article provides a methodological appraisal of the published assay description. The study tested 107 medicines using a radioreceptor assay at specified concentrations and reported activity in atropine-equivalent units. The present article does not repeat the laboratory work, reanalyze raw results, or create new medication categories. Its approach distinguishes the tested preparation and concentration, the assay signal, the assumptions used to relate that signal to usual exposure, and the further evidence needed for a clinical outcome claim. The principal interpretation is that laboratory activity can support biological plausibility while leaving individual exposure and outcome questions unresolved. The original findings remain attributed to Chew and colleagues; no synthetic UnifiedACB value, pediatric conversion, or route-independent risk estimate is derived.

Introduction

The phrase “anticholinergic activity” can describe a laboratory signal, a clinical source category, or an observed adverse effect, depending on context. These meanings should not be interchanged. A study can be valuable at one level without directly measuring the others.

The objective is to clarify what the Chew study contributes to an evidence map. The article focuses on the logic of measurement and interpretation rather than reproducing the drug table. It retains the distinction between the published experiment and the educational analysis presented here.

Methods

This is a narrative methodological appraisal of the published study description and its relationship to the source-specific evidence model used by UnifiedACB. No systematic literature search or new experiment was performed. The appraisal asks four questions: what was tested, what the assay measured, how concentration context entered the interpretation, and which clinical claims remained outside the design.

Chew and colleagues used a radioreceptor assay with rodent brain tissue and a labeled ligand, examining six concentrations for each medicine. Drug-free serum was included in assay samples. Reported activity used atropine equivalents; for medicines with detectable activity, the investigators considered average steady-state peak concentrations in older adults when relating the laboratory findings to exposure. Chew et al., 2008

For the present interpretation, the assay result is treated as a measurement under those experimental conditions. The concentration tested, the preparation, the assay system, and the reference standard belong to the result. They should not be discarded when the finding is summarized in an educational article or cited by a later scale.

The appraisal does not infer unreported route-specific or pediatric concentrations, does not convert atropine-equivalent units into ordinal categories, and does not reconstruct patient-level exposure from a medicine name. It also does not treat the absence of detectable activity under one set of conditions as proof that every possible pharmacologic or clinical effect is absent.

Results

The published study reported variation across medicines and across tested concentrations, with some activity detected only at the highest concentrations examined. Chew et al., 2008 These are laboratory findings from the original study, not new UnifiedACB observations or a clinical outcome analysis conducted for this article.

The appraisal identifies a sequence of distinct claims: activity was measured in an assay; a concentration context was used to discuss exposure; and a clinician may then consider whether that evidence is relevant to a person’s treatment. The first claim does not automatically establish the last. No patient-specific risk probability, source-consensus score, or universal formulation equivalence follows from the assay result alone.

Discussion

The unit tells us what kind of result we are reading

Atropine-equivalent assay activity is not the same unit as an ordinal burden category. An equivalence within an assay describes the reference used to express its signal. It does not mean the tested medicine is clinically interchangeable with atropine or that the numerical result can be inserted directly into another scale.

The same caution applies when a later publication uses laboratory evidence as one input to an expert classification. The later category belongs to that later method. Its existence does not retroactively change what the original experiment measured. An evidence map should keep the chain of citation and transformation visible.

Exposure assumptions need their own evidence

A concentration used to contextualize an experiment is not a measured concentration in every patient taking that medicine. Individual administration history, product, route, and other clinical factors may differ from the experimental assumptions. A medication name therefore cannot supply the entire bridge between the assay and an individual outcome.

This is especially important when a result is applied to another formulation or population. An ingredient-level match can establish relevance for further review, but it cannot prove that the same assay-level exposure occurs. The correct summary identifies the assumption instead of hiding it inside a generalized category.

A clinical outcome is another measurement

Cognition, dry mouth, bowel symptoms, and other outcomes require clinical observation or study. A biologically plausible mechanism can motivate such work but does not replace it. A result in one outcome also does not establish all other outcomes associated with the broad term “anticholinergic.”

For that reason, laboratory evidence and outcome evidence should be reported alongside one another without being collapsed. Agreement can strengthen an interpretation; disagreement may reflect differences in exposure, measurement, or population. Neither situation is solved by averaging incomparable values.

Negative findings also have boundaries

No detected activity under tested conditions is a meaningful experimental result. It should remain tied to the method and range of concentrations examined. It is different from an absent entry in a published scale and different again from a clinical trial showing no association with a specified outcome.

Those distinctions protect against both overstatement and dismissal. A negative assay finding should not become a universal safety claim, while an absent scale entry should not be treated as though an assay had actually been performed and returned zero. Each evidence state has its own provenance.

Limitations

This appraisal relies on the published study description and does not verify raw laboratory measurements or reproduce the assay. It does not provide a complete pharmacokinetic evaluation for any medicine and does not assess every later use of the Chew findings in burden scales.

The experiment’s population-related concentration context, assay conditions, and tested medicines limit the inferences that can be made from it. The study should not be generalized into a pediatric dosing rule, a route-independent clinical effect, or a patient-level treatment decision. No new public medication values have been derived in this article.

Conclusion

Chew 2008 contributes a defined laboratory evidence layer. Its value is preserved by retaining the assay method, concentration context, and original units. Clinical interpretation requires additional evidence about actual exposure and outcomes, while source-native scale classifications remain separate records with their own methods and versions.

References

1. Chew ML, et al. Anticholinergic activity of 107 medications commonly used by older adults. J Am Geriatr Soc. 2008;56:1333-1341. Source
2. Vennard O, Stewart C, Tolia M, Soiza RL, Myint PK. Anticholinergic Medication Burden Scales: A Systematic Review. J Am Geriatr Soc. 2026;74(6):1771-1784. Source
3. Carnahan RM, et al. The Anticholinergic Drug Scale as a measure of drug-related anticholinergic burden: associations with serum anticholinergic activity. J Clin Pharmacol. 2006;46:1481-1486. Source
4. Rudolph JL, et al. The anticholinergic risk scale and anticholinergic adverse effects in older persons. Arch Intern Med. 2008;168:508-513. Source
5. Lisibach A, Benelli V, Ceppi MG, et al. Quality of anticholinergic burden scales and their impact on clinical outcomes: a systematic review. Eur J Clin Pharmacol. 2021;77(2):147-162. Source

Disclosure

Funding: None. Conflict of interest: None declared for the UnifiedACB educational project.

Educational evidence summary. This content does not provide patient-specific medical advice and does not replace clinical judgment, medication reconciliation, or prescribing guidance.