- magnesium sulfate heptahydrate
POM: Prescription only medicine
This information is intended for use by health professionals
Magnesium Sulfate 50% w/v Solution for Injection or Infusion
Magnesium sulfate (heptahydrate) 50% w/v (approximately 2mmol Mg2+ /mL).
Solution for injection or infusion.
(a) Treatment of magnesium deficiency in hypomagnesaemia.
(b) Prevention and control of generalised seizures in patients with severe pre- eclampsia or eclampsia.
Dosages should be adjusted according to the patient's needs and responses. Plasma levels should also be monitored during treatment.
(a) Treatment of magnesium deficiency in hypomagnesaemia:
Up to 160mmol Mg2+ by slow intravenous infusion (in glucose 5%) for up to 5 days, may be required to replace the deficit (allowing for urinary losses). Concentrations of no higher than 20% w/v should be given intravenously.
Treatment may require repetition, for example during prolonged intravenous nutrition magnesium deficiency can occur, then parenteral doses of magnesium are of the order of 10 to 20mmol Mg2+ daily (often about 12mmol Mg2+ daily).
Dosage for the elderly is similar to that for younger adults. Magnesium Sulfate 50% w/v Solution for Injection or Infusion should not be given to children. Appropriate reductions in dosage should be made for patients with renal impairment.
(b) Prevention and control of seizures associated with severe pre-eclampsia and eclampsia:
An initial intravenous (IV) loading dose of typically 4g (approximately 16mmol Mg2+) given slowly over a period of 20 minutes or so, at a strength no higher than 20% w/v, is followed by ideally an IV infusion, or if this is not possible by regular intramuscular (IM) injections as follows:
Intravenous Maintenance Regimen: The loading dose is followed by an intravenous infusion of 1g (approximately 4mmol Mg2+) per hour, continued for 24 hours after the last fit.
Intramuscular Maintenance Regimen: The loading dose is followed by 5g (approximately 20mmol Mg2+), usually in 50% solution, as deep IM injection into the upper outer quadrant of each buttock. The intramuscular injection is painful.
Maintenance therapy is a further 5g every 4 hours continued for 24 hours after the last fit (provided the respiratory rate is >16 per minute, urine output >25mL per hour and knee jerks are present).
Recurrent convulsions: In both the IV and IM regimens, if convulsions recur, a further 2 - 4g (approximately 8 - 16mmol Mg2+), depending on the woman's weight, 2g if less than 70kg, is given IV over 5 minutes.
Appropriate reductions in dosage should be made for patients with renal impairment: a suggested dose reduction in severe renal impairment is a maximum of 20g (approximately 80mmol Mg2+) over 48 hours.
Use of Magnesium Sulfate 50% w/v Solution for Injection or Infusion is contraindicated in patients with known hypersensitivity to magnesium and its salts, hepatic encephalopathy, hepatic failure, renal failure, myasthenia gravis or cardiac disease.
Magnesium salts should be administered with caution to patients with impaired renal function; appropriate reductions in dosage should be made. Magnesium salts should be administered with caution to those receiving digitalis glycosides. Parenteral administration of magnesium salts may enhance the effects of neuromuscular blocking agents or of central nervous system depressants.
Magnesium Sulfate 50% w/v Solution for Injection or Infusion should not be used in hepatic coma if there is a risk of renal failure.
Muscle relaxants: Non-depolarising muscle relaxants such as tubocurarine are enhanced by parenteral magnesium salts.
Nifedipine: profound hypotension was produced in two women who were given oral nifedipine (Martindale, 30th Ed).
Magnesium Sulfate 50% w/v Solution for Injection or Infusion can be administered to a patient with eclampsia if the condition is life threatening to mother and baby.
Magnesium sulfate can cause skeletal adverse effects when administered continuously for more than 5 to 7 days to pregnant women. There are retrospective epidemiological studies and case reports documenting foetal adverse effects including hypocalcaemia, skeletal demineralisation, osteopenia and other skeletal adverse effects with maternal administration of magnesium sulfate for more than 5 to 7 days. The clinical significance of the observed effects is unknown.
If prolonged or repeated exposure to magnesium sulfate occurs during pregnancy monitoring of neonates for abnormal calcium or magnesium levels and skeletal adverse effects should be considered.
Excessive administration of magnesium leads to the development of hypermagnesaemia. Symptoms of hypermagnesaemia may include nausea, vomiting, flushing, thirst, hypotension due to peripheral vasodilation, drowsiness, confusion, loss of tendon reflexes due to neuromuscular blockade, muscle weakness, respiratory depression, cardiac arrhythmias, coma and cardiac arrest.
Acute ingestion of magnesium sulfate and similar magnesium containing compounds may also cause gastrointestinal irritation and watery diarrhoea.
Metabolism and nutrition disorders
Electrolyte/fluid abnormalities (hypophosphataemia, hypertonic dehydration).
There have been isolated reports of maternal and foetal hypocalcaemia with high doses of magnesium sulfate (see section 4.6).
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard or search for MHRA yellow Card in the Google Play or Apple App store.
Appropriate action should be taken to reduce the blood level of magnesium to avoid hypermagnesaemia. Neuromuscular blockade associated with hypermagnesaemia may be reversed with calcium salts such as calcium gluconate, which should be administered intravenously in a dose equivalent to 2.5 to 5 mmol of calcium.
Pharmacotherapeutic group: IV additives - electrolyte solution.
ATC code: B05XA05
Serum magnesium levels in the range of 1.5 - 2.5mmol/L cause vasodilation in the peripheral and coronary circulation and corresponding increases of 20 - 25% in cardiac output and coronary blood flow. There is little change in heart rate or blood pressure. The Atrium-His interval is slightly prolonged as a result of the electrophysiological actions of magnesium. Any direct inhibition is offset by the reflex response to a drop in peripheral vascular resistance and the QT interval is unchanged, thus the function of the SAN is little altered. Within this concentration range there are no detectable effects on CNS function or neuromuscular transmission. At a serum magnesium level of 1 - 3mmol/L platelet disaggregation has been reported, possibly mediated by stimulation of prostacyclin release from the vascular endothelium.
The concentration of magnesium in plasma is normally tightly regulated in the range of 0.75 - 0.95mmol/L. Small and clinically irrelevant amounts are excreted in the breast milk. The major excretory pathway is renal, and both oral and intravenous loads are rapidly eliminated in this way. In renal impairment there may be accumulation of magnesium.
The potential for magnesium toxicity is greater in parenteral administration than with oral dosing. At plasma concentrations of up to 4mmol/L the only adverse effect likely to be seen is flushing due to peripheral vasodilation. At about 4 - 5mmol/L, concentration dependent toxicity is heralded by loss of drop-tendon reflexes, then successively by hypotension, bradycardia, and ultimately neuromuscular blockade leading to respiratory arrest.
When given intravenously magnesium sulfate has an immediate onset of action; its duration of activity is about 30 minutes. The onset of action of intramuscular magnesium sulfate is about one hour and its duration of action is three to four hours.
Magnesium sulfate has been used for many years and its adverse reaction and clinical profile are well understood, therefore no further data are provided.
Bulk Water for Injections
Store between 2 – 25°C.
Magnesium Sulfate 50% w/v Solution for Injection or Infusion is presented in 2mL, 5mL and 10mL type 1 glass ampoules and in 20mL, 50mL and 100mL type 1 glass vials closed with a bromobutyl rubber stopper with an aluminium tamper-proof flip-top cap. The product is packed into cartons containing 10 ampoules, 1 vial or 10 vials. Both pack sizes may not be available at the same time.
A 25% or 50% solution should be used for intramuscular administration. Magnesium Sulfate 50% w/v Solution for Injection or Infusion must be diluted before intravenous administration. Concentrations of up to 20% are usually used.
Chemical and physical in-use stability has been demonstrated for both 50% and diluted (20% w/v) solutions when stored protected from light in l0mL polypropylene syringes in the refrigerator and at 25°C for 28 days. From a microbiological point of view, the product should be used immediately. If not used immediately, in-use storage times and conditions prior to use are the responsibility of the user and would normally not be longer than 24 hours at 2 to 8°C, unless dilution has taken place in controlled and validated aseptic conditions.
Only use the solution if it is particle free.
For single use only. Unused solution should be discarded in an appropriate manner.
Torbay and South Devon NHS Foundation Trust,
Devon, UK, TQ4 7FG
01/2000 / 01/2005
Wilkins Drive, Paignton, TQ4 7FG
+44 (0)1803 660000
+44 (0)7824 889143
+44 (0)1803 664707
+44 (0)1803 664707