WW MAGNES 50%/2ML INJECTION

Indications

• Hypomagnesaemia
• Magnesium deficiency
• Chronic magnesium loss
• Drug-induced hypomagnesaemia

Dosage

Children: Refer to the BNF for Children for specific dosing guidance, as pediatric doses are not detailed in the BNF.

Adults: For treatment and prevention of magnesium deficiency, the recommended dosage is 4–8 mmol (equivalent to approximately 97.2 mg of magnesium) three times a day, with adjustments made based on serum magnesium levels.

Mechanism of action

Magnesium citrate functions primarily through its high osmolality, which draws significant amounts of fluid into the colonic lumen. Additionally, it may stimulate fluid excretion via cholecystokinin release and activate muscle peristalsis, promoting gastrointestinal motility.

Pharmacodynamics

The onset of action for magnesium citrate can occur as quickly as 30 minutes after administration, with a mean onset time of approximately 2 hours. The maximum effect typically occurs around 4 hours post-administration. Its efficacy is significantly influenced by the individual's hydration status, as adequate fluid intake enhances its therapeutic action.

Pharmacokinetics

Magnesium citrate is absorbed in the gastrointestinal tract, and its bioavailability can vary depending on the formulation and individual factors such as renal function. The renal impairment may necessitate caution as magnesium levels can accumulate in cases of severe dysfunction. Regular monitoring of serum magnesium levels is recommended, especially for long-term use.

Adverse effects

• Diarrhoea (with high doses)
• Faeces soft (with high doses)
• Fatigue (long term use)
• Gastrointestinal irritation (with high doses)

Precautions

• Caution in patients with disorders of cardiac conduction
• Avoid in severe renal impairment

Pregnancy

Magnesium citrate is generally considered safe during pregnancy, but it should be used under medical advice.

Breast-feeding

Magnesium citrate is excreted in breast milk; caution is advised when administering to breastfeeding mothers.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Chewable tablets (each containing magnesium citrate equivalent to 97.2 mg)
• Oral solution (various concentrations available)
• Capsules (available in various strengths)

Indications

• Pre-eclampsia
• Eclampsia
• Severe acute asthma
• Continuing respiratory deterioration in anaphylaxis
• Hypomagnesaemia
• Emergency treatment of serious arrhythmias

Dosage

Adults: Initial dose of 4 g, administered as a bolus over 5-15 minutes, followed by an intravenous infusion of 1 gram/hour for 24 hours after the

Mechanism of action

Magnesium sulfate acts primarily by blocking peripheral neuromuscular transmission through the reduction of acetylcholine release at the myoneural junction. It also inhibits calcium influx through dihydropyridine-sensitive, voltage-dependent channels, leading to relaxation of vascular smooth muscle. Additionally, it exerts a cathartic effect by remaining unabsorbed in the intestinal tract, creating an isotonic solution that retains water within the bowel lumen.

Pharmacodynamics

As a small, colorless crystal, magnesium sulfate functions as an anticonvulsant and electrolyte replenisher. It directly inhibits action potentials in myometrial muscle cells, uncoupling excitation and contraction, which decreases the frequency and force of uterine contractions. The drug is also increasingly recognized for its efficacy in managing various dysrhythmias, including torsades de pointes, and those caused by tricyclic antidepressant overdose or digitalis toxicity.

Pharmacokinetics

Magnesium sulfate is administered intravenously or intramuscularly. The onset of action varies, with intravenous administration leading to rapid therapeutic effects. It is distributed throughout the body fluids and has a half-life that can vary significantly based on renal function. Clearance is primarily renal, thus caution is advised in patients with renal impairment due to the increased risk of toxicity. Monitoring of serum magnesium levels is recommended during prolonged therapy.

Contra-indications

• Severe renal impairment
• Severe hepatic impairment
• Rapid bowel evacuation
• Severe dehydration
• Myasthenia gravis

Adverse effects

• Nausea
• Vomiting
• Flushing
• Hypotension
• Drowsiness
• Confusion
• Reflexes absent
• Respiratory depression
• Muscle weakness
• Arrhythmias
• Coma
• Hypermagnesaemia
• Hypomagnesaemia
• Bone demineralisation
• Osteopenia

Interactions

• Calcium channel blockers may enhance the effects of magnesium sulfate
• Neuromuscular blocking agents may have additive effects
• Caution with other medications that can cause renal impairment

Precautions

• Monitor blood pressure and respiratory rate
• Monitor urinary output
• Assess for signs of hypermagnesaemia
• Use with caution in elderly and debilitated patients

Pregnancy

Magnesium sulfate is often used in pregnancy for conditions such as pre-eclampsia and eclampsia. However, excessive doses in the third trimester can cause neonatal respiratory depression.

Breast-feeding

Magnesium sulfate is excreted in breast milk but is generally considered safe during breastfeeding.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Intravenous solution
• Intramuscular injection
• Oral solution

Mechanism of action

It mainly works through its property of high osmolality which will draw large amounts of fluid into the colonic lumen. There is also a possible stimulation of fluid excretion by cholecystokinin release and activation of muscle peristalsis.

Pharmacodynamics

The onset of action can be as early as 30 minutes after administration with a mean onset time of approximately 2 hours and a maximum action of 4 hours. The effect of magnesium citrate is highly dependent on the individual's hydration status.

Mechanism of action

Magnesium is the second most plentiful cation of the intracellular fluids. It is essential for the activity of many enzyme systems and plays an important role with regard to neurochemical transmission and muscular excitability. Magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction. Additionally, Magnesium inhibits Ca²⁺ influx through dihydropyridine-sensitive, voltage-dependent channels. This accounts for much of its relaxant action on vascular smooth muscle. CATHARTIC ACTION RESULTS FROM FACT THAT MGSO4 IS NOT ABSORBED FROM INTESTINAL TRACT, & THUS RETAINS SUFFICIENT WATER WITHIN LUMEN OF BOWEL TO MAKE AN ISOTONIC SOLN. IN EVENT...SALT IS GIVEN IN HYPERTONIC SOLN, SOURCE OF WATER WOULD BE BODY FLUIDS, &...DEHYDRATING ACTION IS EXERTED. /HEPTAHYDRATE, USP/ EXACT MECHANISM OF.../CNS/ DEPRESSANT ACTIVITY IS NOT FULLY KNOWN; HOWEVER, EXCESS MAGNESIUM APPEARS TO DECR AMT OF ACETYLCHOLINE LIBERATED BY MOTOR NERVE IMPULSE. /HEPTAHYDRATE INJECTION USP/ Isolated myometrial strips were obtained from humans undergoing elective cesarean section at term pregnancy and Wistar albino rats on gestational days 19-21. These strips were mounted in organ baths for recording of isometric tensions. The effect of magnesium sulfate, isradipine, and ritodrine on the amplitude and frequency of spontaneous contractions was compared. ... Ritodrine (10-8-10-5 M) concentration-dependently inhibited the frequency and amplitude of spontaneous contractions of myometrial strips. At 10-4 M, tachyphylaxis of ritodrine occurred and contractions started again. Magnesium sulfate (10-7-10-4 M) inhibited the frequency but did not change the amplitude of the spontaneous contractions. Isradipine (10-7-10-4 M) had a concentration-related inhibitor effect on both the frequency and amplitude of the spontaneous contractions. The effects of magnesium sulfate, isradipine, and ritodrine were considerably similar in myometrium strips obtained from pregnant rats and humans. ...

Pharmacodynamics

Magnesium sulfate is a small colorless crystal used as an anticonvulsant, a cathartic, and an electrolyte replenisher in the treatment of pre-eclampsia and eclampsia. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions. Magnesium sulfate is gaining popularity as an initial treatment in the management of various dysrhythmias, particularly torsades de pointes, and dyrhythmias secondary to TCA overdose or digitalis toxicity.