Antimyasthenics are given by mouth or by injection to treat myasthenia gravis. Neostigmine may also be given by injection as a test for myasthenia gravis. Sometimes neostigmine is given by injection to prevent or treat certain urinary tract or intestinal disorders. In addition, neostigmine or pyridostigmine may be given by injection as an antidote to certain types of muscle relaxants used in surgery.

These medicines are available only with your doctor's prescription in the following dosage forms:

Oral
• Ambenonium
  • Tablets (U.S.)
• Neostigmine
  • Tablets (U.S. and Canada)
• Pyridostigmine
  • Syrup (U.S.)
  • Tablets (U.S. and Canada)
  • Extended-release tablets (U.S. and Canada)

Parenteral
• Neostigmine
  • Injection (U.S. and Canada)
• Pyridostigmine
  • Injection (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For the antimyasthenics, the following should be considered:

Allergies?Tell your doctor if you have ever had any unusual or allergic reaction to ambenonium, bromides, neostigmine, or pyridostigmine. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy?Antimyasthenics have not been reported to cause birth defects; however, muscle weakness has occurred temporarily in some newborn babies whose mothers took antimyasthenics during pregnancy.

Breast-feeding?Antimyasthenics have not been reported to cause problems in nursing babies.

Children?Although there is no specific information comparing use of antimyasthenics in children with use in other age groups, these medicines are not expected to cause different side effects or problems in children than they do in adults.

Older adults?Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults. Although there is not much information comparing use of antimyasthenics in the elderly with use in other age groups, these medicines are not expected to cause different side effects or problems in older people than they do in younger adults.

Other medicines?Although certain medicines should not be used together at all, in other cases 2 different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking an antimyasthenic, it is especially important that your health care professional knows if you are using any of the following:

• Demecarium (e.g., Humorsol) or
• Echothiophate (e.g., Phospholine Iodide) or
• Isoflurophate (e.g., Floropryl) or
• Malathion (e.g., Prioderm)?Using these medicines with antimyasthenics may result in serious side effects

• Guanadrel (e.g., Hylorel) or
• Guanethidine (e.g., Ismelin) or
• Mecamylamine (e.g., Inversine) or
• Procainamide (e.g., Pronestyl) or
• Trimethaphan (e.g., Arfonad)?The effects of these medicines may interfere with the actions of the antimyasthenics

• Intestinal blockage or
• Urinary tract blockage or
• Urinary tract infection?These medicines may make the condition worse

Your doctor may want you to take this medicine with food or milk to help lessen the chance of side effects. If you have any questions about how you should be taking this medicine, check with your doctor.

Take this medicine only as directed. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. To do so may increase the chance of side effects.

If you are taking this medicine for myasthenia gravis :

• When you first begin taking this medicine, your doctor may want you to keep a daily record of:
  • the time you take each dose.
  • how long you feel better after taking each dose.
  • how long you feel worse.
  • any side effects that occur.

This is to help your doctor decide whether the dose of this medicine should be increased or decreased and how often the medicine should be taken in order for it to be most effective in your condition.

Dosing?

The dose of these medicines will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets or teaspoonfuls of syrup that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking these medicines.

For ambenonium
• For oral dosage form (tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 5 milligrams (mg) three or four times per day. Then, if needed, the dose will be adjusted by your doctor.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 300 micrograms (mcg) per kilogram (kg) (136 mcg per pound) of body weight or 10 mg per square meter of body surface area. This dose may be divided into three or four smaller doses. If needed, the total daily dose will be increased to 1.5 mg per kg (0.68 mg per pound) of body weight or 50 mg per square meter of body surface area. This dose may be divided into three or four smaller doses.

For neostigmine
• For oral dosage form (tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 15 milligrams (mg) every three or four hours. Then, the dose is 150 mg taken over a twenty-four-hour period.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 2 mg per kilogram (kg) (0.91 mg per pound) of body weight or 60 mg per square meter of body surface area. This dose may be divided into six to eight smaller doses.
• For injection dosage form:
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 500 micrograms (mcg) injected into a muscle or under the skin.
    • Children?The dose is based on body weight and must be determined by your doctor. It is usually 10 to 40 mcg per kg (4.5 to 18.2 mcg per pound) of body weight, injected into a muscle or under the skin, every two or three hours.
  • For urinary tract or intestinal disorders:
    • Adults and teenagers?The usual dose is 250 to 500 mcg, injected into a muscle or under the skin, as needed.
    • Children?Use and dose must be determined by your doctor.

For pyridostigmine
• For oral dosage forms (syrup and tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 30 to 60 milligrams (mg) every three or four hours. Then, the dose is 60 mg to 1.5 grams (usually 600 mg) per day.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 7 mg per kilogram (kg) (3.2 mg per pound) of body weight or 200 mg per square meter of body surface area. This dose may be divided into five or six smaller doses.
• For long-acting oral dosage form (extended-release tablets):
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 180 to 540 mg one or two times per day.
    • Children?Dose must be determined by your doctor.
• For injection dosage form:
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 2 mg, injected into a muscle or vein, every two or three hours.
    • Children?The dose is based on body weight and must be determined by your doctor. It is usually 50 to 150 micrograms (mcg) per kg (22.7 to 68.1 mcg per pound) of body weight, injected into a muscle every four to six hours.

Missed dose?

If you miss a dose of this medicine, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage?

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the syrup form of pyridostigmine from freezing.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Your doctor may want you to take this medicine with food or milk to help lessen the chance of side effects. If you have any questions about how you should be taking this medicine, check with your doctor.

Take this medicine only as directed. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. To do so may increase the chance of side effects.

If you are taking this medicine for myasthenia gravis :

• When you first begin taking this medicine, your doctor may want you to keep a daily record of:
  • the time you take each dose.
  • how long you feel better after taking each dose.
  • how long you feel worse.
  • any side effects that occur.

This is to help your doctor decide whether the dose of this medicine should be increased or decreased and how often the medicine should be taken in order for it to be most effective in your condition.

Dosing?

The dose of these medicines will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets or teaspoonfuls of syrup that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking these medicines.

For ambenonium
• For oral dosage form (tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 5 milligrams (mg) three or four times per day. Then, if needed, the dose will be adjusted by your doctor.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 300 micrograms (mcg) per kilogram (kg) (136 mcg per pound) of body weight or 10 mg per square meter of body surface area. This dose may be divided into three or four smaller doses. If needed, the total daily dose will be increased to 1.5 mg per kg (0.68 mg per pound) of body weight or 50 mg per square meter of body surface area. This dose may be divided into three or four smaller doses.

For neostigmine
• For oral dosage form (tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 15 milligrams (mg) every three or four hours. Then, the dose is 150 mg taken over a twenty-four-hour period.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 2 mg per kilogram (kg) (0.91 mg per pound) of body weight or 60 mg per square meter of body surface area. This dose may be divided into six to eight smaller doses.
• For injection dosage form:
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 500 micrograms (mcg) injected into a muscle or under the skin.
    • Children?The dose is based on body weight and must be determined by your doctor. It is usually 10 to 40 mcg per kg (4.5 to 18.2 mcg per pound) of body weight, injected into a muscle or under the skin, every two or three hours.
  • For urinary tract or intestinal disorders:
    • Adults and teenagers?The usual dose is 250 to 500 mcg, injected into a muscle or under the skin, as needed.
    • Children?Use and dose must be determined by your doctor.

For pyridostigmine
• For oral dosage forms (syrup and tablets):
  • For myasthenia gravis:
    • Adults and teenagers?At first, the dose is 30 to 60 milligrams (mg) every three or four hours. Then, the dose is 60 mg to 1.5 grams (usually 600 mg) per day.
    • Children?The dose is based on body weight or size and must be determined by your doctor. The total daily dose is usually 7 mg per kilogram (kg) (3.2 mg per pound) of body weight or 200 mg per square meter of body surface area. This dose may be divided into five or six smaller doses.
• For long-acting oral dosage form (extended-release tablets):
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 180 to 540 mg one or two times per day.
    • Children?Dose must be determined by your doctor.
• For injection dosage form:
  • For myasthenia gravis:
    • Adults and teenagers?The usual dose is 2 mg, injected into a muscle or vein, every two or three hours.
    • Children?The dose is based on body weight and must be determined by your doctor. It is usually 50 to 150 micrograms (mcg) per kg (22.7 to 68.1 mcg per pound) of body weight, injected into a muscle every four to six hours.

Missed dose?

If you miss a dose of this medicine, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage?

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the syrup form of pyridostigmine from freezing.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.