Pyridostigmine

Myasthenia gravis, paralytic ileus and post-operative urinary retention.

Posology

Myasthenia gravis

Adults

Doses of 30 to 120mg are given at intervals throughout the day when maximum strength is needed (for example, on rising and before mealtimes). The usual duration of action of a dose is 3 to 4 hours in the daytime but a longer effect (6 hours) is often obtained with a dose taken on retiring for bed.

The total daily dose is usually in the range of 5 - 20 tablets but doses higher than these may be needed by some patients.

Paediatric population

Children under 6 years old should receive an initial dose of half a tablet (30mg) of Pyridostigmine; children 6 - 12 years old should receive one tablet (60mg). Dosage should be increased gradually, in increments of 15 - 30mg daily, until maximum improvement is obtained. Total daily requirements are usually in the range to 30 - 360mg.

Other Indications (paralytic ileus, post-operative urinary retention)

Adults

The usual dose is 1 to 4 tablets (60 - 240mg) per day.

Paediatric population

The usual dose is 15 - 60mg per day.

The frequency of these doses may be varied according to the needs of the patient.

Special populations

Elderly

There are no specific dosage recommendations for Pyridostigmine in elderly patients.

Renal impairment

Pyridostigmine is mainly excreted unchanged by the kidney, therefore lower doses may be required in patients with renal disease and treatment should be based on titration of drug dosage to effect.

Hepatic impairment

There are no specific dosage recommendations for Pyridostigmine in patients with hepatic impairment.

Method of administration

For oral use

Pyridostigmine is contra-indicated in patients with:

-

- Mechanical gastro-intestinal or urinary obstruction

Extreme caution is required when administering Pyridostigmine to patients with obstructive respiratory diseases like bronchial asthma and chronic obstructive pulmonary disease (COPD).

Care should also be taken in patients with:

- Arrhythmias such as bradycardia and AV block(elderly patients may be more susceptible to dysrhythmias than the young adult)

- Recent coronary occlusion

- Hypotension,

- Vagotonia

- Peptic ulcer

- Epilepsy or Parkinsonism

- Hyperthyroidism

When relatively large doses of Pyridostigmine are taken by myasthenic patients it may be necessary to give atropine or other anticholinergic drugs to counteract the muscarinic effects. It should be noted that the slower gastro-intestinal motility caused by these drugs may affect the absorption of Pyridostigmine.

In all patients the possibility of "cholinergic crisis", due to overdosage of Pyridostigmine , and its differentiation from "myasthenic crisis", due to increased severity of the disease, must be borne in mind. Both types of crisis are manifested by increased muscle weakness, but whereas myasthenic crisis may require more intensive anticholinesterase treatment, cholinergic crisis calls for immediate discontinuation of this treatment and institution of appropriate supportive measures, including respiratory assistance.

The requirement for Pyridostigmine is usually markedly decreased after thymectomy or when additional therapy (steroids, immunosuppressant drugs) is given.

Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Due to miosis and accommodation disorders caused by pyridostigmine bromide or an inadequate treatment of Myasthenia gravis, Pyridostigmine may impair visual acuity and consequently the ability to react as well as the ability to drive and use machines.

As with all cholinergic products, Pyridostigmine may have unwanted functional effects on

the autonomic nervous system. Muscarine-like adverse effects may be exhibited as nausea, vomiting, diarrhoea, abdominal cramps, increased peristaltic and increased bronchial secretion, salivation, bradycardia and miosis.

The primary nicotinic effects are muscle spasms, fasciculation and muscular weakness.

Adverse reactions are listed below according to system organ class and frequency. Frequencies are defined according to the following convention:

Very common (>1/10), Common (>1/100 to <1/10), Uncommon (>1/1,000 to <1/100), Rare (>1/10,000 to <1/1,000) Very rare (<1/10,000) Not known (cannot be estimated from the available data)

Eye disorders

Frequency not known: Miosis, increased lacrimation, accommodation disorders

Cardiac disorders

Frequency not known: Arrhythmia (including bradycardia, tachycardia, AV block), as well as syncope and hypotension

Respiratory, thoracic and mediastinal disorders

Frequency not known: Increased bronchial secretion combined with bronchoconstriction

Gastrointestinal disorders

Frequency not known: Nausea, vomiting, diarrhoea, abdominal cramps, gastrointestinal hypermotility, salivary hypersecretion

Skin and subcutaneous tissue disorders

Frequency not known: Rash (disappears usually soon after ceasing of medication. Bromide containing medicines should no longer be used.) Hyperhydrosis

Musculoskeletal and connective tissue disorders

Frequency not known: Increased muscle weakness fasciculation, tremors and muscle cramps or muscle hypotonia

Renal and urinary disorders

Frequency not known: Urinary urgency

Because these symptoms may be an indication of cholinergic crisis, the physician should be notified immediately to clarify the diagnosis

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme Website: www.mhra.gov.uk/yellowcard

Overdosage may lead to “cholinergic crisis” characterised by severe muscarinic and nicotinic symptoms of marked muscle weakness. Cardiovascular and respiratory failure may occur.

Signs of overdosage due to muscarinic effects may include abdominal cramps, increased peristalsis, diarrhoea, nausea and vomiting, increased bronchial secretions, salivation, hyperhydrosis and miosis. Nicotinic effects consist of muscular cramps, fasciculations and general weakness up to paralysis.

Hypotension up to cardiovascular collapse, bradyarrhythmia, up to cardiac arrest may also occur.

Central nervous system effects may include agitation, confusion, slurred speech, nervousness, irritation, visual hallucinations.

Artificial ventilation should be instituted if respiration is severely depressed.

Atropine sulphate 1 to 2mg intravenously is an antidote to the muscarinic effects. Doses may be repeated every 5 to 30 minutes as needed.

Pharmacotherapeutic group: Nervous system, parasympathomimetics, anticholinesterases, pyridostigmine , ATC code: N07AA02

Pyridostigmine is an antagonist to cholinesterase, the enzyme which normally destroys acetylcholine. The action of Pyridostigmine can briefly be described, therefore, as the potentiation of naturally occurring acetylcholine. Pyridostigmine has a more prolonged action than Prostigmin (neostigmine) although it is somewhat slower to take effect (generally taking 30 - 60 minutes). Because it has a weaker "muscarinic" action than Prostigmin, it is usually much better tolerated by myasthenic patients in whom the longer action is also an advantage.

Oral pyridostigmine bromide is poorly absorbed. Maximum plasma concentrations occur at 1 to 2 hours and it is eliminated by the kidney largely unchanged with a half-life of 3 to 4 hours.

There are no preclinical data of relevance to the prescriber, which are additional to those already included in other sections of the SmPC.

Not applicable.

No special requirements for disposal.