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4.4 Special warnings and precautions for use
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Abrupt discontinuation of amantadine may result in worsening of Parkinsonism or in symptoms resembling neuroleptic malignant syndrome (NMS), as well as in cognitive manifestations (e.g. catatonia, confusion, disorientation, worsening of mental status, delirium). Symmetrel should not be stopped abruptly in patients who are treated concurrently with neuroleptics. There have been isolated reports of precipitation or aggravation of neuroleptic malignant syndrome or neuroleptic-induced catatonia following the withdrawal of amantadine in patients taking neuroleptic agents. A similar syndrome has also been reported rarely following withdrawal of amantadine and other anti-parkinson agents in patients who were not taking concurrent psychoactive medication.
Amantadine has anticholinergic effects, it should not be given to patients with untreated angle closure glaucoma.
Hypothermia has been observed in children, especially in those younger than 5 years of age. Caution should be exercised when prescribing Symmetrel to children for the prevention and treatment of influenza type A virus (see also section 4.2 Posology and method of administration).
4.8 Undesirable effects
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Adverse reactions (Table 1) are ranked under heading of frequency, the most frequent first, using the following convention: very common (greater than or equal to 1 in 10); common (less than or equal to 1 in 100, less than 1 in 10); uncommon (greater than or equal to 1 in 1,000, less than 1 in 100); rare (greater than or less than 1 in 10,000, less than 1 in 1,000) very rare (less than 1 in 10,000), not known (where no valid estimate of the incidence has been derived).
NB: The incidence and severity of some of the adverse reactions, noted below, varies according to the dosage and nature of the disease under treatment.
Table 1
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Blood and lymphatic system disorders:
Very rare: leucopenia, reversible elevation of liver enzymes
Nervous system disorders:
Common: anxiety, elevation of mood, lightheadedness, headache, lethargy, hallucinations, nightmares, ataxia, slurred speech, blurred vision, loss of concentration, nervousness, depression, insomnia, myalgia. Hallucinations, confusion and nightmares1
Uncommon: confusion, disorientation, psychosis, tremor, dyskinesia, convulsions, neuroleptic malignant-like syndrome
Not known: Delirium, hypomanic state and mania2
Eye disorders:
Rare: corneal lesions, e.g. punctate subepithelial opacities which might be associated with superficial punctate keratitis, corneal epithelial oedema, and markedly reduced visual acuity
Cardiac disorders:
Very common: oedema of ankles, livedo reticularis3
Common: palpitations, orthostatic hypotension
Very rare: heart insufficiency/failure
Gastrointestinal disorders:
Common: dry mouth, anorexia, nausea, vomiting, constipation
Rare: diarrhoea
Skin and subcutaneous tissue disorders:
Common: diaphoresis.
Rare: exanthema
Very rare: photosensitisation
Renal and urinary disorders:
Rare: urinary retention, urinary incontinence
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1more common when amantadine is administered concurrently with anticholinergic agents or when the patient has an underlying psychiatric disorder.
2reported but their incidence cannot be readily deduced from the literature.
3usually after very high doses or use over many months.
4.9 Overdose
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Overdose with Symmetrel can lead to fatal outcome.
Signs and symptoms: Neuromuscular disturbances and symptoms of acute psychosis are prominent. Central nervous system: Hyperreflexia, motor restlessness, convulsions, extrapyramidal signs, torsion spasms, dystonic posturing, dilated pupils, dysphagia, confusion, disorientation, delirium, visual hallucinations, myoclonus. Respiratory system: hyperventilation, pulmonary oedema, respiratory distress, including adult respiratory distress syndrome. Cardiovascular system: cardiac arrest and sudden cardiac death have been reported. Sinus tachycardia, arrhythmia, hypertension. Gastrointestinal system: nausea, vomiting, dry mouth. Renal function: urine retention, renal dysfunction, including increase in BUN and decreased creatinine clearance.
5.1 Pharmacodynamic properties
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Pharmacotherapeutic group: Antiparkinsonian agent
ATC code N04B B01
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