Hypocalcaemic tetany

Rapid intravenous injection of the sodium salt of EDTA depletes blood calcium levels and produces hypocalcaemic tetany, but, carefully administered, this agent can be used to treat hypercalcaemia and to overcome digitalis-induced arrhythmia by adjusting the Ca2+/K+ balance61). The ready availability of calcium ion from extracirculatory stores enables slow (drip) infusion of sodium EDTA without untoward effects. Continued over several days, calcium is mobilised from bone and calcium EDTA is excreted in the urine but plasma calcium levels are not greatly affected62). Although it has been little explored, drip infusion of sodium EDTA,... 

Haskell LP. Hypocalcaemic tetany induced by hypertonic-phosphate enema [letter]. Lancet 1985 ii 1433. 

A 46-year-old woman, known to have radiation enteritis with chronic diarrhoea and associated malabsorption syndrome, presented to the outpatient department complaining of severe tingling of recent on.set in her hands and feet. The patient had a pa.st history of hypocalcaemic tetany 18 months previously, but serum calcium had since remained normal on therapy with I a-hydroxycholecalciferol. 0.75 pg daily, plus oral calcium supplements. 

A low hydrogen ion concentration occurs as a result of hyperventilation, in which carbon dioxide is blown off in the lungs. The condition occurs in certain otherwise normal people who hyperventilate as a reaction to stress. A frequent result is a reduced concentration of ionized calcium in the extracellular fluid, the condition of hypocalcaemia. The effect is hypocalcaemic tetany, which consists of involuntary uncoordinated contractions of skeletal muscles and of bizarre subjective sensations and numbness. These symptoms and signs are due to hyperexcitability of peripheral nerve fibres, which fire action potentials spontaneously. The mechanism is that the reduced hydrogen ion concentration results in dissociation of complexes between plasma albumin and hydrogen ions, with a binding of plasma calcium to the albumin sites which are vacated by the hydrogen ions. Hence there is a fall in the concentration of ionized calcium in the extracellular fluid and this results in the nervous hyperexcitability. 

Indicate why hyperventilation may result in hypocalcaemic tetany include the importance of extracellular [H ] variation. 

PENTAMIDINE ISETIONATE (INTRAVENOUS) FOSCARNET SODIUM Risk of hypocalcaemia Unclear possibly additive hypocalcaemic effects Use extreme caution with intravenous pentamidine monitor serum calcium (correct before the start of treatment), renal function and signs of tetany closely. Stop one drug if necessaiy... 

Deficiency causes hypocalcaemia, resulting in rickets in children or osteomalacia in adults. Hypocalcaemic convulsions and tetany can occur. 

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