Magnesium

Magnesium

Lucy Walker

Question• Mrs Jones is a 65 year old lady with an Adenocarcinoma

of lung. She has just completed her sixth cycle of chemotherapy. You are asked to see her in Day Hospice as she complains of muscle spasms and fatigue. What is the most likely drug cause for her symptoms?

A. Alendronic acidB. CisplatinC. DocetaxelD. EtoposideE. Pemetrexed

Learning Outcomes:

• By the end of the talk, you will be able to:– List symptoms of hypomagnesaemia– Give 5 causes of low magnesium– Suggest tests for low magnesium– Advise someone on replacement

Overview:

• The Science Bit• Signs and Symptoms of High and Low

magnesium levels• Investigations• Potential relevance• Management

The Science Bit• Second most abundant intracellular ion after potassium

• Less than 1% of total body magnesium is found in blood

• Serum levels tightly controlled by homeostasis

• Roles in the body:– Regulates energy production (ATP activation)– Vital for protein synthesis– Needed by over 300 enzyme reactions– Bone mineralisation– Muscle relaxation– Neurotransmitter – Regulates K+ and Ca2+ channels in cell membranes

What regulates levels?

• Small Intestine– Absorbed predominantly from ileum

• Kidney– Excreted in glomerulus, predominantly reabsorbed

in Loop of Henle• Bone

Where does it come from?

• Food!• Decline in dietary magnesium content over

the last century

• Which foods???

TOP FIVE FOODS

Features of high and low MgHypomagnesaemia• Neuromuscular

– Weakness– tremor– Muscles cramps/ spasms– Tetany– Chvostek’s sign– Hyperreflexia– Paraesthesia

• CNS– Anxiety– Apathy– Depression– Coma– Delirium– Choreiform movements– Fatigue– Lethargy– Nystagmus– Seizures– Personality change

• Cardiovascular– Prolonged QT– Arrhythmia esp Torsade de pointes

• Others– Increased pain?– Hypokalaemia– Hypocalcaemia– Hypophosphataemia– Nausea

Hypermagnesaemia

• Neuromuscular– Muscle weakness– Hypotonia– Hyporeflexia

• Sensation of warmth (IV)• Flushing (IV)• CNS

– Drowsiness– Slurred speech– Double vision– Delirium

• Cardiovascular– Hypotension– Arrhythmias

• Other– Nausea– Thirst– Respiratory depression

Why does it get low?• Reduced intake

• Reduced absorption/ increased GI tract loss– Small bowel resection, cholestasis, pancreatic insufficiency,

diarrhoea, vomiting, stoma, fistula, prolonged PPI use, laxative use

• Increased renal losses– Congenital or acquired tubular defects– Alcoholism– Drug induced eg platinum based chemotherapy agents, loop

diuretics, ACE inhibitors, aminoglycosides

• Endocrine disturbance– Hyperthyroidism, SIADH, hyperparathyroidism, DM

When should we think about it

• Pain– Natures NMDA receptor antagonist

• Refeeding syndrome– Probably underdiagnosed in our population

• Fatigue– But probably not first line??

DR VICTORIA MONTGOMERY ON MAGNESIUM FOR PAIN

COMING SOON TO AN EBM NEAR YOU…

How to check levels• Normal serum levels are 0.7- 1.05mmol/L– Patients with low magnesium can still fall within

this range

• Magnesium Loading Test (see PCF)

• 24 hour urine Magnesium

• Resistant low potassium?

How to replace (1)

• Oral replacement is generally insufficient to correct deficiency but may help with maintenance. Aim to prescribe 24mmol per 24 hours.

• Oral preparations include:• Magnesium Glycerophosphate• Magnesium Aspartate• Magnesium Hydroxide• Magnesium Sulphate

• Side effects:– diarrhoea

• Encourage magnesium rich diet

How to replace (2)

• Severe (<0.5mmol/L) or symptomatic hypomagnesaemia generally needs IV replacement

• Need daily replacement until symptoms and plasma magnesium correct

• Policies vary widely by trust. PCF has a protocol as alternative

• Beware:– Avoid in severe renal failure or heart block

• Side effects:– Flushing and warmth

• If really necessary can consider IM route (painful) and limited data for CSCI

Should I be interested in a high Mg?

• Fairly rare• Usually patients with renal failure who take

magnesium containing medications• Consider stopping antacids

• IV Calcium Gluconate reverses the effects if symptomatic severe hypermagnesaemia but this is very rare

Question• Mrs Jones is a 65 year old lady with an Adenocarcinoma

of lung. She has just completed her sixth cycle of chemotherapy. You are asked to see her in Day Hospice as she complains of muscle spasms and fatigue. What is the most likely drug cause for her symptoms?

A. Alendronic acidB. CisplatinC. DocetaxelD. EtoposideE. Pemetrexed

Take Home Messages

• Magnesium is a growing area of interest• Serum levels can be within normal range

despite significant body depletion• Hypomagnesaemia is very common• Consider if non-specific symptoms that aren’t

responding to conventional approaches• Initial replacement is most successful if given

intravenously

References• PCF4 page 545

• Fawcett WJ, Haxby EJ & Male DA. (1999) Magnesium: physiology and pharmacology. British Journal of Anaesthesia. 83(2):302-20

• Crosby V, Elin RJ, Twycross R, Mihalyo M & Wilcock A. (2013) Magnesium. JPSM 45(1): 137-44

• Brogan G, Exton L, Kurowska A & Tookman A. (2000) The importance of low magnesium in palliative care: two case reports. Palliat Med 14: 59-61

• Beckwith MC & Botros LR. (1998) Clinical implications of hypomagnesemia. Journal of Pharmaceutical Care in Pain and Symptom control 6(1): 65-77

• Lopez-Saca et al (2013) Hypomagnesaemia as a possible explanation behind episodes of severe pain in cancer patients receiving palliative care. Supportive Cancer Care 21:649-652

• Schor et al (2013) Proton pump inhibitor induced hypomagnesaemia: a case report. Journal of Supportive Oncology 11(2):103

• Miripri N & Patel P (2002) Mosby’s Crash Course Renal and Urinary Systems. Elsevir Science, Edinburgh