Antimyasthenic (Oral, Parenteral)

Antimyasthenics form a group of a medication that is most commonly prescribed to treat myasthenia gravis, a condition affecting muscle strength.

Overview

Antimyasthenics is a prescription-only drug that is used to treat myasthenia gravis, a condition affecting muscle strength. It can be taken orally or via injection, and is part of a group of medications that relax the muscles and prevent involuntary movements.

Myasthenia gravis is a rare condition with long term health implications for sufferers. [ref 1] The condition can affect people of any age group, but is typically found starting in women under the age of 40 and men over the age of 60. The illness causes muscle weakness, which often does not persist for consistent lengths of time – rather coming and going in spurts. The muscles that are most commonly affected by this condition centre around the face – in particular the eyes and eyelids. It also affects the muscles that control facial expressions, swallowing, speaking and chewing. As a result, sufferers of myasthenia gravis may experience difficulty in doing any of these activities when they are going through a period of muscle weakness. The condition is not limited to the face; it is also known to affect other parts of the body in rarer cases.

One of the most common drugs types used to treat the symptoms of myasthenia gravis are antimyasthenics.

Antimyasthenics are drugs taken by the mouth or by injection and come in a variety of forms. They help to treat this condition by relaxing and strengthening muscles. This group of medication is also sometimes used to treat other conditions, such as various urinary tract infections and intestinal diseases. It is also occasionally given to patients as a muscle relaxant during invasive surgery.

There are various drugs that make up the antimyasthenics group – some common ones include ambenonium, neostigmine and pyridostigmine. This type of medicine is available only through prescriptions issued by a health care professional.

There are various brand names for antimyasthenics, but they all contain the same active ingredients, so should be treated in exactly the same way. These brands are:

  • Razadyne
  • Razadyne ER
  • Razadyne IR
  • Exelon
  • Mestinon
  • Prostigmin Bromide
  • Mestinon Timespan
  • Aricept

Conditions treated

  • Myasthenia gravis
  • Urinary tract infections
  • Intestinal diseases
  • Muscle relaxant

Type of medicine

  • Oral
  • Parenteral / injection

The medication is generally available in a variety of forms to aid consumption. These include:

  • Tablet
  • Capsule
  • Disintegrating tablets
  • Syrup
  • Extended Release Tablets
  • Extended Release Capsules
  • Solution

Side effects

As with any medication, there are various side effects that patients can expect when taking antimyasthenics. Some of these side effects are fairly common and therefore nothing to worry about. However, if patients' symptoms persist, or if they experience any of the rarer more serious symptoms, they should contact their doctor immediately for advice.

Some of the common side effects of antimyasthenics include – but are not limited to – the list below.

  • Diarrhea
  • Increased saliva production in the mouth
  • Vomiting or nausea
  • Pain in the stomach
  • Cramps in the abdomen

You may, in some cases, also experience some of the following side effects. These symptoms are not usually experienced, but there have been some reports of them being related to taking antimyasthenics:

  • Sore throat (sometimes experienced with fever, or otherwise on its own)
  • Skin rash, redness or itchiness
  • Excessive watering of the eyes
  • Smaller pupils than normal
  • Increased need for urination

Side effects of antimyasthenics are not limited to those listed; you may find that you experience other changes to the body while taking the medication, particularly at the beginning of a treatment cycle while your physicality adapts to the drug. [ref 2]

If you think you have taken too much medication, you may also experience some of the side effects commonly experienced during overdose. If you find that you are suffering from any of these symptoms, you should seek medical advice urgently and immediately.

  • Blurry vision
  • Instability on the feet, or clumsiness and lack of coordination
  • Severe diarrhea
  • Convulsions / seizures
  • Intense muscle weaknesses, especially acute in the neck, shoulders, arms and tongue
  • Twitching
  • Cramps in the muscles
  • A shortage of breath or difficulty breathing / restricted airflow [ref 3]
  • Coughing or wheezing
  • Nervousness, fear or extreme anxiety
  • Restlessness or heightened irritability
  • Tightness in the chest area and inability to take a deep breath
  • Swelling or redness of the skin, or skin rash
  • Pain in the location of the injection
  • A slower heartbeat than normal
  • Slurred speech
  • Cramps in the stomach

Dosage

The dose you are prescribed of this medication will depend on several factors – and will be different from patient to patient. The following doses are averages only; your doctor may prescribe you a different dose, but do not attempt to alter it yourself – always stick to your doctor's recommended dose.

Ambenonium

For those tablets to be administered orally as a treatment for myasthenia gravis, the normal starter dose is 5 milligrams (mg) for teenagers and adults. This is taken three to four times per day, with meals ideally. After an initial period, your doctor may look to increase that dose. Children are usually started on a dose of 300 micrograms (mcg) per kilogram of body weight. As with adults, the dosage for children is usually divided into three or four takings throughout each day. After the initial period, the dose for children could be increased to around 1.5 mg per kg of body weight, taken three to four times per day.

Neostigmine

This is commonly taken in the form of oral tablets and is usually prescribed at 15 mg per day for adults and teenagers, taken every three to four hours throughout the day. The increased dose after a successful trial is then typically 150 mg, which is spread evenly over a 24-hour period. For children, it is usually recommended to start the dosage at 2 mg per kg of body weight. It is recommended that this is then divided into six to eight doses, to be taken at regular intervals throughout the course of a day.

This type of medication can also be taken as an injection, and this is arguably a much easier option as it prevents the need for constant doses throughout the day. For adults and teenagers, the usual dose for this is 500 micrograms, and this is injected underneath the skin into a muscle. However, for children, it is necessary to inject every two to three hours. A dose of between 10 and 40 micrograms per kg of body weight is the norm.

When used to treat urinary tract diseases, recommended starting doses are between 250 to 500 mcg, which is usually injected under the skin or in a muscle. For children, this drug is not usually prescribed for this purpose, but a doctor will decide on its implementation on a case by case basis.

Pyridostigmine

For medication that is prescribed in the form of oral tablets or syrup, a starting dose for adults and teenagers is usually set at somewhere between 30 and 60 mg per three to four hour period. After an initial period, the dose per taking is between 60 mg and 1.5 grams, which adds up to around 600 mg per 24-hour period. For children, the dosage is again down to individual body weight, but, as a general rule, sits at around 7 mg per kg of body weight.

Major drug interactions

Some medications can react with others, altering their effectiveness and occasionally leading to a variety of unwanted and unnecessary side effects. You should always tell your doctor if you are on any other form of medication. Not all interactions are serious – some can be very mild – but it is always best to be upfront with your doctor before starting a new medication. There may be instances in which you are taking another drug, but you may still be able to take antimyasthenics; it may just alter the dose that your doctor prescribes to you.

There are a variety of medicines that have been found to interact with antimysthenics. The list below contains those drugs that have been found to have major interactions. However, it is by no means an exhaustive list.

  • Amifampridine
  • Amisulpride
  • Atropine
  • Mesoridazine
  • Metoclopramide
  • Sparfloxacin
  • Bepridil
  • Bromopride
  • Cisapride
  • Thioridazine
  • Dronedarone
  • Posaconazole
  • Saquinavir
  • Fluconazole
  • Ketoconazole
  • Pimozide
  • Piperaquine
  • Terfenadine
  • Ziprasidone

Warnings

There are various warnings for those taking this medication, which should be considered before starting a course.

Allergies

You should always tell your doctor if you are aware of any allergies you have to medicines – in this group of medication or others. There are also other types of allergies that may be provoked as a result of taking this type of medication. Intolerances to preservatives, types of food, dyes and even animals can all trigger a reaction from taking this medication.

Children

Although there is no evidence to suggest that taking antimyasthenics can cause harm to children, there are also no studies that have been taken to show the long-lasting impact on minors. You should therefore consider the potential for different reactions to the medication when taken by children.

Geriatric

As with children, there is not a lot of information available as to how well these drugs work when taken by older people. There are no studies to confirm that side effects of antimyasthenics will be the same in elderly patients as they are in younger adults. The potential risk to an elderly patient's health should also be considered before deciding upon a course of antimyasthenics.

Pregnancy and breast feeding

Although there has been no evidence to suggest that antimyasthenics can cause birth defects, there are some reports of muscle weakening in some new-borns where the mother has taken a course of antimyasthenic drugs at any point during the pregnancy. Fortunately there is no evidence to show that antimyasthenics have any impact on nursing babies.

Alcohol

As with many prescribed drugs, it is strongly advisable not to drink excessive amounts of alcohol during a course of treatments. Alcohol consumption can alter with the effectiveness of this medication; therefore, it is recommended to only drink in moderation when taking antimyasthenics. For women, this usually means one drink per day and for men two drinks per day. Alcohol can not only impact on the effectiveness of antimyasthenics; it can also lead to heightened side effects and increased drowsiness. Also, the antimyasthenics can lead to a tendency to lower the body's tolerance of alcohol.

Other diseases

Other drugs can react with and impact the effectiveness of your antimyasthenics – as can other diseases and conditions that you might suffer from. Always tell your doctor if you suffer from one of any other conditions, as this may affect the dosage or type of medication that is suitable for you.

Monitoring of patients taking antimyasthenics

If you are prescribed a course of antimyasthenics, it is important that your progress is monitored by a trained healthcare professional – particularly in the early stages of taking your medication. This is also particularly important if you are coming off another drug and onto this one, as there may be overlapping side effects as a result. These types of side effects can often be more severe, or can be more problematic if they persist. If you experience significant side effects after transferring to antimyasthenics, your doctor may decide to prescribe you a different type of medication.

Missing a dose

If you take your antimyasthenics orally, you may forget to take one from time to time. If this is the case, there is no need to worry. Simply take the dose as soon as you remember. However, if you find that it is closer to your next dose, skip the missed one entirely. Do not try to make up for missed medication by taking more of it in your next dose. This will not make any positive difference and could bring on unwanted side effects.

Overdose

If you take more than your prescribed dosage of antimyasthenics, make sure you contact a medical professional for advice as soon as possible, particularly if you are experiencing any of the symptoms associated with overdose (listed in the side effects section above).

Storage

It is widely recommended that all antimyasthenics are stored at room temperature (21 degrees centigrade), and out of direct sunlight or heat sources. This ensures that the drugs remain at maximum effectiveness.

No matter what form your antimyasthenics come in, always make sure you store this medication in a secure place that is out of the reach of children or animals – at all times. Many of these tablets or syrups come in secure containers that lock into place when closed, making them impossible for children or animals to open and consume. You should always use these types of containers where supplied as they have been designed to prevent misuse.

If your medication does not come supplied in a tamper-proof container, make sure you store it in a secure cupboard or a high shelf, out of the sight of those for whom it is not intended. You should not transfer your medication to other types of containers, as these generic tubs do not typically come with safety caps, so are not tamper resistant or child-proof.

Disposal

If you no longer require your medication, you must dispose of it in the correct manner. In the United States, there are various drug recycling schemes that will collect your medication from you and dispose of it in a safe way. These take-back schemes are available to residents across the country and were formed to prevent disposed drugs getting into the wrong hands. Run by the FSA, take-back schemes offer is simple and hassle-free way to get rid of your medication.

Of course, there will be some instances where using an FSA-approved take-back scheme may not be possible – such as in some remote locations. If this is the case, there are various steps you can take to make sure you dispose of your antimyasthenics. [ref 4] However, as a rule, you should mix your unwanted antimyasthenics with a substance that is not fit for human or animal consumption – such as soil or dirt. You should then place the mixture into a sealable bag and then place into your normal household trash cans.

Summary

There have been various studies that show the effectiveness of antimyasthenics in treating myasthenia gravis. However, the consumption of these medicines should be treated with caution and care – as many courses require multiple intakes throughout the day. If doses are missed, the drug will be less effective at treating the effects of myasthenia gravis. There are also a range of possible side effects that need to be closely monitored, particularly in newer patients.

Various drugs are known to interact with antimyasthenics, so patients should proceed with caution if they are taking any other form of medication. Avoid any unpleasant or dangerous symptoms by always being upfront with healthcare professionals about other medication and co-existing health conditions.

This is a drug that is most effective when it is strictly monitored, and taken with food or milk to lower the possibility of side effects. The drug requires a very high level of commitment by the patient to stick to various doses required throughout the day, and it is often required that patients keep a diary of their progress to ensure that prescribed dosages are at the correct level. However, with the right level of commitment from the patient, along with close monitoring by the health care professional, antimyasthenics can be an effective long-term treatment for easing the discomfort and long-term impact of of myasthenia gravis.

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Last Reviewed:
December 24, 2017
Last Updated:
April 04, 2018
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