Why was edrophonium discontinued? The Reasons Behind the Tensilon Test's End

October 5, 2025 •

3 min read

In 2018, the U.S. Food and Drug Administration (FDA) discontinued the use of edrophonium, effectively ending the era of the Tensilon test as a diagnostic tool for myasthenia gravis. This decision was driven by the test's inherent limitations and the advent of safer, more accurate diagnostic methods.

Quick Summary

Edrophonium was discontinued by the FDA due to unreliable results from the Tensilon test, including high rates of false positives and negatives. Significant safety concerns and the development of superior, safer diagnostic alternatives like serologic antibody testing also drove the change.

Key Points

End of an Era: The FDA officially discontinued edrophonium (Tensilon test) in 2018 for diagnosing myasthenia gravis.
Unreliable Results: The Tensilon test suffered from high rates of both false-positive and false-negative outcomes, leading to misdiagnoses.
Significant Risks: Edrophonium posed serious safety concerns, including the potential for severe adverse effects like bradycardia and respiratory distress.
Superseded by Better Science: Modern diagnostic techniques, such as serologic antibody testing and electrophysiologic studies, proved to be far more accurate and safer.
Improved Patient Care: The shift away from edrophonium represents an advancement in medical practice, prioritizing patient safety and diagnostic certainty over a rapid, but risky, bedside test.

The Historical Role and Mechanism of Edrophonium

For decades, edrophonium, sold under the brand name Tensilon, was a cornerstone in the diagnosis of myasthenia gravis (MG), an autoimmune neuromuscular disorder. Edrophonium is a short-acting acetylcholinesterase inhibitor. Its mechanism of action involves inhibiting the acetylcholinesterase enzyme, which is responsible for breaking down the neurotransmitter acetylcholine in the neuromuscular junction (NMJ). By blocking this breakdown, edrophonium causes acetylcholine levels to increase temporarily. In a patient with MG, this brief increase in acetylcholine can temporarily overcome the effects of the antibodies that block or destroy the acetylcholine receptors, leading to a temporary improvement in muscle strength. This dramatic but fleeting improvement was the basis of the Tensilon test, a diagnostic procedure performed at the bedside.

The Problems with Inaccuracy: False Positives and Negatives

One of the most significant factors contributing to edrophonium's discontinuation was its unreliability. The Tensilon test was plagued by both false-positive and false-negative results, which could lead to incorrect diagnoses and inappropriate treatment pathways.

False-Positive Results: A false positive occurred when a person without MG showed temporary muscle improvement after receiving edrophonium. This could be a result of the placebo effect or observer bias. Such a misdiagnosis could cause unnecessary anxiety and expose patients to treatments they did not need.
False-Negative Results: On the other hand, a false-negative result occurred when a person with MG did not show any improvement after the injection. This often happened in patients with specific subtypes of MG, such as those with muscle-specific receptor kinase (MuSK) antibodies or seronegative MG, who do not have the typical acetylcholine receptor antibodies.

This suboptimal sensitivity and specificity made it difficult for clinicians to rely solely on the Tensilon test, pushing them toward more definitive, objective diagnostic methods.

Significant Safety Concerns

Another major reason for the end of the edrophonium era was the drug's potential for severe adverse effects. The administration of edrophonium required close medical monitoring and the availability of emergency resuscitation equipment.

Adverse effects of edrophonium included:

Bradycardia (slow heart rate) and other arrhythmias
Bronchospasm, which could lead to respiratory distress
Seizures
Nausea, vomiting, diarrhea, and other gastrointestinal distress
Excessive salivation and sweating

Patients with certain heart conditions or asthma were at particular risk and required extreme caution or were excluded from the test. The risk of respiratory arrest was also a serious concern. The availability of safer and more accurate testing methods made these risks unnecessary for a diagnosis.

The Rise of Safer, More Accurate Diagnostics

Medical science has since developed superior alternatives that offer greater precision and reduced risk for patients. These modern diagnostic tools ultimately made the continued use of edrophonium obsolete for diagnosing MG.


Diagnostic Method	Mechanism	Advantages	Limitations
Edrophonium (Tensilon) Test	Short-acting acetylcholinesterase inhibitor; temporary increase in acetylcholine	Rapid results (minutes)	High rate of false positives and negatives, Significant risk of adverse effects, Subjective results
Serologic Antibody Testing	Detects pathogenic antibodies (e.g., anti-AChR, anti-MuSK)	High specificity and sensitivity, Objective results, Safer procedure	Results take longer than a bedside test, Some cases (seronegative MG) yield no antibody detection
Repetitive Nerve Stimulation (RNS)	Measures compound muscle action potential (CMAP) decline	Objective, Quantifiable results	Less useful for ocular MG, Less sensitive than single-fiber EMG
Single-Fiber Electromyography (SFEMG)	Measures neuromuscular jitter	High sensitivity, Especially for ocular MG	Technically demanding procedure

Conclusion: A Medical Advancement

The discontinuation of edrophonium marks a significant milestone in the evolution of diagnostic medicine for myasthenia gravis. The transition from a risky and sometimes misleading bedside test to a portfolio of accurate, objective, and safe diagnostic tools reflects the progress in our understanding of the disease's pathophysiology. While edrophonium served its purpose for many years, the advent of serologic testing and advanced electrophysiologic studies offered a path forward that prioritized both patient safety and diagnostic certainty. The decision by regulatory bodies like the FDA to remove it from the market was a necessary step, ensuring that modern medical practice adheres to the highest standards of care. For anyone interested in the history of medicine, the story of edrophonium's decline is a compelling case study in how better science can ultimately replace outdated methods.

Outbound Link

For a deeper look into the historical context and the shift in diagnostic approaches, the National Institutes of Health (NIH) provides articles detailing the modern diagnostics for MG.

Frequently Asked Questions

The Tensilon test, which used edrophonium, was historically used to help diagnose myasthenia gravis (MG). A temporary improvement in muscle strength after the injection suggested a positive result.

The U.S. Food and Drug Administration (FDA) discontinued the use of edrophonium for diagnostic purposes in 2018.

The test produced false positives due to the placebo effect or observer bias, and false negatives often occurred in patients with certain MG antibody types (like MuSK) or seronegative MG.

Risks included bradycardia, bronchospasm, seizures, and severe gastrointestinal issues. Due to these risks, the test required emergency equipment to be available.

Today, doctors use more reliable methods like serologic antibody testing (looking for specific antibodies) and electrophysiologic studies such as repetitive nerve stimulation (RNS) and single-fiber electromyography (SFEMG).

While primarily known for the Tensilon test, edrophonium was also used to reverse the effects of certain neuromuscular blocking agents used during surgery, though other drugs are now often preferred. It is no longer widely available.

Edrophonium's effect was based on a subjective, temporary observation of muscle improvement, while modern tests rely on objective, quantifiable data from blood tests or nerve function studies, providing a much higher degree of accuracy and safety.