magnesium glycerophosphate: clinical use

Prescribing considerations

• Confirm hypomagnesaemia and consider its cause before replacement.
• Oral tablets are unsuitable as the sole acute correction for severe symptomatic hypomagnesaemia.
• Consider reduced absorption after extensive bowel resection.
• Look for associated hypokalaemia and hypocalcaemia.

Contraindications and cautions

• Hypersensitivity to the active substance or relevant excipients
• Severe renal impairment
• Hyperphosphataemia
• Phenylketonuria for Neomag because it contains aspartame
• Relevant hereditary sugar-intolerance disorders for the sorbitol- and sucrose-containing product

Monitoring

• Serum magnesium, particularly in children and renal impairment
• Renal function and clinical features of magnesium accumulation
• Potassium and calcium where magnesium deficiency is confirmed
• Response, gastrointestinal tolerance and interacting medicines

Clinical pharmacology

Magnesium is absorbed mainly in the jejunum and ileum and participates in enzyme activity, neuromuscular transmission and muscle excitability. Renal filtration and tubular reabsorption predominantly regulate absorbed magnesium, so accumulation is more likely when renal clearance is substantially impaired.

Formulation and product differences

• Neomag contains aspartame and may be quartered, chewed or swallowed with water; its score does not create equal doses.
• Magnesium 4mmol Chewable Tablets contain sorbitol, sucrose and sodium and should be chewed.
• Excipients create product-specific restrictions, so products should not be treated as identical without checking the relevant SmPC.