Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 8/8/2022

Drug Summary

What Is Enlon?

Enlon (edrophonium injection) is a short and rapid-acting cholinergic drug used to reverse the effects of certain medications used to prevent muscle contractions during surgical procedures. The brand name Enlon is discontinued, but generic versions may be available.

What Are Side Effects of Enlon?

Common side effects of Enlon include:

  • watery eyes,
  • vision problems,
  • changes in your voice,
  • nausea,
  • vomiting,
  • diarrhea,
  • stomach pain,
  • weakness, or
  • muscle twitching

Enlon may cause serious side effects including:

  • hives,
  • difficulty breathing,
  • swelling of your face, lips, tongue, or throat,
  • slow heartbeats,
  • weak or shallow breathing,
  • lightheadedness,
  • vision problems,
  • eye redness or watering,
  • seizure,
  • trouble speaking or swallowing,
  • cough with mucus,
  • wheezing,
  • shortness of breath,
  • increased salivation,
  • nausea,
  • vomiting,
  • diarrhea,
  • stomach pain,
  • muscle weakness,
  • twitching or involuntary movement,
  • increased sweating,
  • urinating more than usual, and
  • loss of bowel or bladder control

Get medical help right away, if you have any of the symptoms listed above.

Seek medical care or call 911 at once if you have the following serious side effects:

  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheartedness, or passing out;
  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

Dosage for Enlon

The intravenous dosage of Enlon for adults: A tuberculin syringe containing 1 mL (10 mg) of Enlon is prepared with an intravenous needle, and 0.2 mL (2 mg) is injected intravenously within 15 to 30 seconds. The needle is left in situ. Only if no reaction occurs after 45 seconds is the remaining 0.8 mL (8 mg) injected.

What Drugs, Substances, or Supplements Interact with Enlon?

Enlon may interact with other drugs. Tell your doctor all medications and supplements you use.

Enlon During Pregnancy or Breastfeeding

Enlon may be harmful to a fetus. Tell your doctor if you are pregnant before you receive this medication. Consult your doctor before breastfeeding.

Additional Information

Our Enlon (edrophonium injection) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

Drug Description


Enlon (edrophonium injection) ® is a short and rapid-acting cholinergic drug. Chemically, edrophonium chloride is ethyl (m-hydroxyphenyl) dimethylammonium chloride.

Each mL contains, in a sterile solution, 10 mg edrophonium chloride compounded with 0.45% phenol as a preservative, and 0.2% sodium sulfite as an antioxidant, buffered with sodium citrate and citric acid, and pH adjusted to approximately 5.4. Structural formula as follows:

Enlon (edrophonium injection) ® is intended for IV and IM use.



Enlon (edrophonium injection) ® is recommended for the differential diagnosis of myasthenia gravis and as an adjunct in the evaluation of treatment requirements in this disease. It may also be used for evaluating emergency treatment in myasthenic crises. Because of its brief duration of action, it is not recommended for maintenance therapy in myasthenia gravis.

Enlon (edrophonium injection) ® is also useful whenever a curare antagonist is needed to reverse the neuromuscular block produced by curare, tubocurarine, gallamine triethiodide or dimethyl-tubocurarine. It is not effective against decamethonium bromide and succinylcholine chloride. It may be used adjunctively in the treatment of respiratory depression caused by curare overdosage.



Enlon (edrophonium injection) ® Test in the Differential Diagnosis of Myasthenia Gravis:1-8

Intravenous Dosage (Adults): A tuberculin syringe containing 1 mL (10 mg) of Enlon (edrophonium injection) ® is prepared with an intravenous needle, and 0.2 mL (2 mg) is injected intravenously within 15 to 30 seconds. The needle is left in situ. Only if no reaction occurs after 45 seconds is the remaining 0.8 mL (8 mg) injected. If a cholinergic reaction (muscarinic side effects, skeletal muscle fasciculations and increased muscle weakness) occurs after injection of 0.2 mL (2 mg), the test is discontinued and atropine sulfate, 0.4 mg to 0.5 mg, is administered intravenously. After one-half hour the test may be repeated.

Intramuscular Dosage (Adults): In adults with inaccessible veins, dosage for intramuscular injection is 1 mL (10 mg) of Enlon (edrophonium injection) ®. Subjects who demonstrate hyperreactivity to this injection (cholinergic reaction), should be retested after one-half hour with 0.2 mL (2mg) of Enlon (edrophonium injection) ® intramuscularly to rule out false-negative reactions.

Dosage (Children): The intravenous testing dose of Enlon (edrophonium injection) ® in children weighing up to 75 lbs is 0.1 mL (1 mg); above this weight, the dose is 0.2 mL (2 mg). If there is no response after 45 seconds, it may be titrated up to 0.5 mL (5 mg) in children under 75 lbs, given in increments of 0.1 mL (1 mg) every 30 to 45 seconds and up to 1 mL (10 mg) in heavier children. In infants, the recommended dose is 0.05 mL (0.5 mg). Because of technical difficulty with intravenous injection in children, the intramuscular route may be used. In children weighing up to 75 lbs, 0.2 mL (2 mg) is injected intramuscularly, in children weighing more than 75 lbs, 0.5 mL (5 mg) is injected intramuscularly. All signs which would appear with the intravenous test appears with the intramuscular test except that there is a delay of two to ten minutes before a reaction is noted.

Enlon (edrophonium injection) ® Test for Evaluation of Treatment Requirements in Myasthenia Gravis: The recommended dose is 0.1 mL to 0.2 mL (1 mg to 2 mg) of Enlon (edrophonium injection) ®, administered intravenously one hour after oral intake of the drug being used in treatment. 1-5 Response will be myasthenic in the undertreated patient, adequate in the controlled patient, and cholinergic in the overtreated patient. Responses to Enlon (edrophonium injection) ® in myasthenic and nonmyasthenic individuals are summarized in the following chart.

  Myasthenic*  Adequate  Cholinergic¡
Muscle Strength    (ptosis, diplopia dysphonia, dysphagia, dysarthria, respiration, Limb strength) Increased No change Decreased
Fasciculations (orbicularis oculi, facial muscles, limb muscles) Absent Present or absent  Present or absent 
Side reactions (lacrimation diaphoresis, salivation, abdominal cramps, nausea, vomiting, diarrhea) Absent  Minimal. Severe

* Myasthenic Response- occurs in untreated myasthenics and may serve to establish diagnosis; in patients under treatment, indicates that therapy is inadequate.

  Adequate Response- observed in treated patients when therapy is stabilized: a typical response in normal individuals. In addition to this response in non-myasthenics, the phenomenon of forced lid closure is often observed in psychoneurotics.

¡ Cholinergic Response- seen in myasthenics who have been overtreated with anticholinesterase drugs.

Enlon (edrophonium injection) ® Test in Crisis: The term crisis is applied to the myasthenic whenever severe respiratory distress with objective ventilatory inadequacy occurs and the response to medication is not predictable. This state may be secondary to a sudden increase in severity of myasthenia gravis (myasthenic crisis), or to overtreatment with anticholinesterase drugs (cholinergic crisis).

When a patient is apneic, controlled ventilation must be secured immediately in order to avoid cardiac arrest and irreversible central nervous system damage. No attempt is made to test with Enlon (edrophonium injection) ® until respiratory exchange is adequate.

Dosage used at this time is most important: If the patient is cholinergic, Enlon (edrophonium injection) ® will cause increased or opharyngeal secretions and further weakness in the muscles of respiration. If the crisis is myasthenic, the test clearly improves respiration and the patient can be treated with longer-acting intravenous anticholinesterase medication. When the test is performed, there should not be more than 0.2 mL (2 mg) Enlon (edrophonium injection) ® in the syringe. An intravenous dose of 0.1 mL (1 mg) is given initially. The patient†s heart action is carefully observed. If, after an interval of one minute, this dose does not further impair the patient, the remaining 0.1 mL (1 mg) can be injected. If no clear improvement of respiration occurs after 0.2 mL (2 mg) dose, it is usually wisest to discontinue all anticholinesterase drug therapy and secure controlled ventilation by tracheostomy with assisted respiration. 5

For Use as a Curare Antagonist: Enlon (edrophonium injection) ® should be administered by intravenous injection in 1 mL (10 mg) doses given slowly over a period of 30 to 45 seconds so that the onset of cholinergic reaction can be detected. This dosage may be repeated whenever necessary. The maximal dose for any one patient should be 4 mL (40 mg). Because of its brief effect, Enlon (edrophonium injection) ® should not be given prior to the administration of curare, tubocurarine, gallamine triethiodide or dimethyl-tubocurarine: it should be used at the time when its effect is needed. When given to counteract curare overdosage, the effect of each dose on the respiration should be carefully observed before it is repeated, and assisted ventilation should always be employed.

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.


ENLON (edrophonium injection) ® (edrophonium chloride injection, USP):

NDC 10019-873-15   15 mL vials

ENLON (edrophonium injection) ® (edrophonium chloride injection, USP) should be stored at controlled room temperature 15°-30°C (59°-86°F).


1. Osserman KE, Kaplan LI. JAMA 1952;150:265.

2. Osserman KE, Kaplan LI., Besson G. J Mt Sinai Hosp 1953;20:165.

3. Osserman KE, Kaplan LI. Arch Neurol Psychiatr 1953;70:385.

4. Osserman KE, Teng P. JAMA 1956;160:153.

5. Osserman KE, Genkins G. Ann Ny Acad Sci 1966;135:312.

6. Tether JE, Second International Symposium Proceedings, Myasthenia Gravis, 1961, p.444.

7. Tether JE, in HF Conn: Current Therapy 1960, Philadelphia, WB Saunders Go, p.551.

8. Tether JE, in HF Conn: Current Therapy 1965, Philadelphia, WB Saunders Co, p.556.

9. Grab D. Johns RJ. JAMA 1958;166:1855.

Side Effects & Drug Interactions


Careful observation should be made for severe cholinergic reactions in the hyperreactive individual. The myasthenic patient in crisis who is being tested with Enlon (edrophonium injection) ® should be observed for bradycardia or cardiac standstill and cholinergic reactions if an overdose is given.

The following reactions common to anticholinesterase agents may occur, although not all of these reactions have been reported with the administration of Enlon (edrophonium injection) ®, probably because of its short duration of action and limited indications:


Increased lacrimation, pupillary constriction, spasm of accommodation, diplopia, conjunctival hyperemia.

CNS:   Convulsions, dysarthria, dysphonia, dysphagia.

Increased tracheobronchial secretions, laryngospasm, bronchiolar constriction, paralysis of muscles of respiration, central respiratory paralysis. 


Arrhythmias (especially bradycardia), fall in cardiac output leading to hypotension. Increased salivary, gastric and intestinal secretion, nausea, vomiting, increased peristalsis, diarrhea, abdominal cramps.

Skeletal Muscle:   Weakness, fasciculations.
Miscellaneous:   Increased urinary frequency and incontinence, diaphoresis.


Care should be given when administering this drug to patients with symptoms of myasthenic weakness who are also on anticholinesterase drugs. Since symptoms of anticholinesterase overdose (cholinergic crisis) may mimic underdosage (myasthenic weakness), their condition may be worsened by the use of this drug. (See OVERDOSAGE section for treatment.)

Warnings & Precautions


Whenever anticholinesterase drugs are used for testing, a syringe containing 1 mg of atropine sulfate should be immediately available to be given in aliquots intravenously to counteract severe cholinergic reactions which may occur in the hypersensitive individual, whether he is normal or myasthenic. Enlon (edrophonium injection) ® should be used with caution in patients with bronchial asthma or cardiac dysrhythmias. The transient bradycardia which sometimes occurs can be relieved by atropine sulfate. Isolated instances of cardiac and respiratory arrest following administration of Enlon (edrophonium injection) ® have been reported. It is postulated that these are vagotonic effects.

Contains sodium sulfite, a sulfite that may cause allergic-type reactions including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible people. The overall prevalence of sulfite sensitivity in the general population is unknown and probably low. Sulfite sensitivity is seen more frequently in asthmatic than in nonasthmatic people.

Usage in Pregnancy: The safety of Enlon (edrophonium injection) ® during pregnancy or lactation in humans has not been established. Therefore, use of Enlon (edrophonium injection) ® in women who may become pregnant requires weighing the drug†s potential benefits against its possible hazards to mother and child.


Patients may develop †anticholinesterase insensitivity for brief or prolonged periods. During these periods the patients should be carefully monitored and may need respiratory assistance. Dosages of anticholinesterase drugs should be reduced or withheld until patients again become sensitive to them.

Overdose & Contraindications


With drugs of this type, muscarine-like symptoms (nausea, vomiting, diarrhea, sweating, increased bronchial and salivary secretions and bradycardia) often appear with overdosage (cholinergic crisis). An important complication that can arise is obstruction of the airway by bronchial secretions. These may be managed with suction (especially if tracheostomy has been performed) and by the use of atropine. Many experts have advocated a wide range of dosages of atropine (for Enlon (edrophonium injection) ®, see atropine dosage below), but if there are copious secretions, up to 1.2 mg intravenously may be given initially and repeated every 20 minutes until secretions are controlled. Signs of atropine overdosage such as dry mouth, flush and tachycardia should be avoided as tenacious secretions and bronchial plugs may form. A total dose of atropine of 5 to 10 mg or even more may be required. The following steps should be taken in the management of overdosage of Enlon (edrophonium injection) ®:

1. Adequate respiratory exchange should be maintained by assuring an open airway and by the use of assisted respiration augmented by oxygen.

2. Cardiac function should be monitored until complete stabilization has been achieved.

3. Atropine sulfate in doses of 0.4 to 0.5 mg should be administered intravenously. This may be repeated every 3 to 10 minutes. Because of the short duration of action of Enlon (edrophonium injection) ® the total dose required will seldom exceed 2 mg.

4. Pralidoxime chloride (a cholinesterase reactivator) may be given intravenously at the rate of 50 to 100 mg per minute; usually the total dose does not exceed 1000 mg. Extreme caution should be exercised in the use of pralidoxime chloride when the cholinergic symptoms are induced by double-bond phosphorous anticholinesterase drugs.9

5. If convulsions occur or shock is present, appropriate measures should be instituted.


Known hypersensitivity to anticholinesterase agents; intestinal and urinary obstructions of mechanical type.

Clinical Pharmacology


Enlon (edrophonium injection) ® is an anticholinesterase drug. Its pharmacologic action is due primarily to the inhibition or inactivation of acetylcholinesterase at sites of cholinergic transmission. Its effect is manifest within 30 to 60 seconds after injection and lasts an average of 10 minutes.

Medication Guide



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