BMA Concise Guide to Medicine & Drugs

Pyridostigmine

Brand name Mestinon

Used in the following combined preparations None

QUICK REFERENCE

Drug group Drug for myasthenia gravis

Overdose danger rating High

Dependence rating Low

Prescription needed Yes

Available as generic No

GENERAL INFORMATION

Pyridostigmine is used to treat myasthenia gravis, an autoimmune disease involving faulty transmission of nerve impulses to the muscles. Pyridostigmine improves muscle strength by prolonging nerve signals, although it does not cure the disease. In severe cases, it may be prescribed with corticosteroids or other drugs. Pyridostigmine may also be used to reverse temporary paralysis of the bowel and urinary retention following surgical operations.

Cholinergic side effects (e.g. nausea, abdominal cramps, increased salivation and sweating, and diarrhoea) usually disappear after reducing the dosage of pyridostigmine, although occasionally an anticholinergic drug such as propantheline is needed to counteract these effects.

INFORMATION FOR USERS

Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses Every 3–4 hours initially. Thereafter, according to the needs of the individual.

Dosage range Adults 300mg–1.2g daily (by mouth) according to response and side effects. Children Reduced dose necessary according to age and weight.

Onset of effect 30–60 minutes.

Duration of action 3–6 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose Take as soon as you remember. If your next dose is due within 2 hours, take a single dose now and skip the next.

Stopping the drug Do not stop the drug without consulting your doctor; symptoms may recur.

OVERDOSE ACTION

Seek immediate medical advice in all cases. You may experience severe abdominal cramps, vomiting, weakness, and tremor. Take emergency action if troubled breathing, unusually slow heart beat, seizures, or loss of consciousness occur.

POSSIBLE ADVERSE EFFECTS

Adverse effects of pyridostigmine are usually dose-related and can be avoided by adjusting the dose. Nausea, vomiting, increased salivation, sweating, abdominal cramps, and diarrhoea are common; discuss with your doctor if you have abdominal cramps or diarrhoea or if any of these other symptoms are severe. Less commonly, the drug may cause watering eyes, small pupils, or a rash (which may result from hypersensitivity to the drug). Consult your doctor if any of these symptoms occur. Muscle twitching or increased muscle weakness may sometimes be due to too large a dose; if these occur, contact your doctor immediately.

INTERACTIONS

General note Drugs that suppress the transmission of nerve signals may oppose the effect of pyridostigmine. Such drugs include aminoglycoside antibiotics, clindamycin, digoxin, procainamide, quinidine, lithium, and chloroquine.

Propranolol may decrease the effectiveness of pyridostigmine.

SPECIAL PRECAUTIONS

Be sure to tell your doctor if:

· You have asthma.

· You have a long-term kidney problem.

· You have heart problems.

· You have had epileptic seizures.

· You have difficulty in passing urine.

· You have a peptic ulcer.

· You have Parkinson’s disease.

· You are taking other medicines.

Pregnancy No evidence of risk to the developing fetus in the first 6 months. Large doses near the time of delivery may cause premature labour and temporary muscle weakness in the baby. Discuss with your doctor.

Breast-feeding No evidence of risk, but the baby should be monitored for signs of muscle weakness.

Infants and children Reduced dose necessary, calculated according to age and weight.

Over 60 Reduced dose may need to be given. Increased likelihood of adverse effects.

Driving and hazardous work Your underlying condition may make such activities inadvisable. Discuss with your doctor.

Alcohol No special problems.

Surgery and general anaesthetics Pyridostigmine interacts with some anaesthetic agents. Make sure your treatment is known to your doctor, dentist, and anaesthetist before any surgery.

PROLONGED USE

Pyridostigmine has been implicated in “Gulf War syndrome” when taken for long periods. However, there is no evidence of this occurring when the drug is used in people with myasthenia gravis.