An acute hypermagnesaemia (either asymptomatic or with acute systemic toxicity) suppresses both the central and the peripheral neural activity by inhibiting acetylcholine release. Systemic toxicity is to be expected from a serum concentration of 2.5 mmol/l, severe neurotoxic side effects appear from 3 mmol/l and above. With concentrations of 2.5-5.0 mmol/l gastrointestinal disturbances (nausea, anorexia, constipation), cystospasm, muscle weakness, lethargy, missing deep-tendon reflexes and disturbed AV-conduction and ventricular stimulus conduction has been observed.
In case of serum magnesium levels of 5-10 mmol/l, arterial hypotension induced by vasodilatation, paralytic ileus, flaccid paralysis and coma have been observed. At a level of more than 10 mmol/l respiratory arrest and cardiac arrest occur.
Symptoms of hypercalcaemia are initially muscle weakness and gastrointestinal disturbances (abdominal pain, constipation, nausea and vomiting). Severe hypercalcaemia is characterised by disturbances of consciousness (e.g. lethargy,disorientation, stupor, in extreme cases also coma). In patients with a serum calcium level of more than 3.5 mmol/l a hypercalcaemic crisis is possible with the symptoms of:
- Polyuria, polydipsia
- Nausea, anorexia, constipation, pancreatitis (infrequent)
- Arrhythmia, shortening of the QT-interval, adynamia, hypertension
- Muscle weakness up to pseudo paralysis
- Psychosis, somnolence up to coma.
Long-term overdosing may lead to the development of an adynamic osteopathy.
Emergency treatment: In addition to symptomatic treatment, the therapy of hypermagnesaemia consists in lowering the magnesium-concentration of the dialysate and in a reduction of the dose of this tablet. During the treatment of hypercalcaemia with a calcium-free dialysate close monitoring of serum calcium concentration is necessary in order to minimise the risk of hypocalcaemia and adverse cardiovascular reactions.