Dostimid

Indications

Pyridostigmine is used to treat myasthenia gravis, a condition in which the immune system disrupts the signals between nerves and muscles, causing muscle weakness and tiredness, drooping eyelids, double vision and difficulty swallowing. It may also be used by doctors to reverse the effect of some muscle relaxants after surgery and, in some cases, for bowel or bladder problems caused by poor muscle movement.

How It Works

Nerves pass messages to muscles using a chemical called acetylcholine. Pyridostigmine blocks the enzyme (cholinesterase) that breaks acetylcholine down, so more of it stays available at the nerve and muscle junction. This improves muscle strength.

Dosage and Administration

The dose is adjusted for each person according to symptoms and is taken as prescribed, usually several times a day spread through waking hours. Some people are advised to take a dose 30 to 60 minutes before meals to help with chewing and swallowing. The injection form is given by a doctor or nurse.

• Take doses at evenly spaced times as advised.
• Do not increase the dose on your own, as too much can cause weakness that looks like the disease getting worse.

Interactions

Some medicines can weaken its effect or worsen myasthenia, including certain antibiotics (Gentamicin and other aminoglycosides, Ciprofloxacin and other fluoroquinolones, Azithromycin), Quinine, Procainamide, beta blockers, Lithium and Magnesium given by injection. Atropine and other anticholinergic medicines oppose its action. It can change the effect of muscle relaxants used in anaesthesia, so tell the anaesthetist you take it. Corticosteroids can at first worsen weakness.

Contraindications

• Allergy to Pyridostigmine or bromide.
• Blockage of the bowel or urinary tract.
• Use with care, or avoid, in uncontrolled asthma.

Side Effects

Common effects come from extra acetylcholine activity: stomach cramps, diarrhoea, nausea, increased saliva and sweating, watery eyes, frequent urination and muscle twitching. Slow heartbeat and low blood pressure can occur.

Get urgent medical help if you have severe muscle weakness, difficulty breathing or swallowing, a very slow heartbeat, fainting, or signs of an allergic reaction such as rash, swelling of the face or wheezing.

Pregnancy and Lactation

Myasthenia gravis needs continued treatment in pregnancy and Pyridostigmine is often used under specialist care, but the injection form should be avoided near delivery unless advised. Only small amounts pass into breast milk; breastfeeding is usually possible, but watch the baby for unusual weakness or feeding problems and discuss with your doctor.

Precautions and Warnings

Use with care in asthma, heart rhythm problems, recent heart attack, epilepsy, Parkinson's disease, stomach ulcer, overactive thyroid and kidney problems (a lower dose may be needed). Too much medicine can cause a cholinergic crisis, with increasing weakness, which can be hard to tell apart from a myasthenic crisis; both need urgent care.

Overdose

Overdose can cause severe stomach cramps, diarrhoea, heavy sweating and saliva, small pupils, slow heartbeat, muscle twitching and serious weakness of breathing muscles. Seek emergency medical help immediately. Atropine and breathing support may be given in hospital.

Therapeutic Class

Cholinesterase inhibitor (parasympathomimetic agent).

Storage

Store below 30°C in a dry place, away from light and out of the reach of children.