# Magnesium Sulphate Regimens and Toxicity

> Pritchard, Zuspan and Dhaka magnesium sulphate protocols, toxicity monitoring and calcium gluconate antidote for NEET-PG Obstetrics and Gynaecology preparation.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/magnesium-sulphate-regimens-and-toxicity
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Williams Obstetrics; WHO Recommendations for Prevention and Treatment of Pre-eclampsia and Eclampsia; D.C. Dutta's Textbook of Obstetrics
- How to cite: "Magnesium Sulphate Regimens and Toxicity", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/magnesium-sulphate-regimens-and-toxicity

## Direct answer

Magnesium sulphate is the drug of choice for seizure prophylaxis and treatment of eclampsia, and the named regimens differ mainly in route and dose. Pritchard combines an intravenous loading dose with repeated intramuscular maintenance, while Zuspan uses intravenous loading followed by continuous infusion. Toxicity shows first as loss of the patellar reflex, then falling respiratory rate and urine output, and calcium gluconate is the antidote.

## What you must remember

- **Pritchard regimen:** 4 g intravenous loading, then 5 g intramuscularly into each buttock, then 5 g intramuscularly every four hours.
- **Zuspan regimen:** intravenous loading followed by a continuous intravenous infusion, continued for about 24 hours after delivery or the last seizure.
- **Dhaka regimen:** a low-dose intramuscular protocol with comparable seizure control in small studies; exact doses should be taken from the institution's protocol.
- **Monitoring before each dose:** patellar reflex present, respiratory rate at least 16 per minute, and urine output of about 30 mL per hour.
- **Toxicity sequence:** loss of patellar reflex first, then respiratory depression, then cardiac arrest.
- **Antidote:** 10% calcium gluconate, 1 g (10 mL) given intravenously slowly over several minutes, repeated if needed.

## A monitoring and toxicity pathway

Magnesium is cleared by the kidney, so monitoring is an ongoing duty rather than a one-time check. The steps below run from loading to antidote. Each step is a point where the infusion can be safely continued, reduced or stopped.

1. **Load and start:** give the intravenous loading dose over the set time, then begin the maintenance regimen chosen by protocol.
2. **Check before each dose:** confirm patellar reflex, respiratory rate and urine output, since reduced output signals accumulation.
3. **Recognise early toxicity:** loss of the knee jerk is the earliest sign, and the infusion is stopped at that point.
4. **Support breathing:** give oxygen and assist ventilation if respiratory depression develops.
5. **Give calcium gluconate:** administer 1 g of 10% calcium gluconate intravenously and repeat if the response is inadequate.
6. **Measure serum levels when unclear:** the therapeutic range is commonly quoted as about 4.8 to 8.4 mg/dL, used mainly when toxicity is suspected.

## Where the exam tries to catch you

Questions here test the sequence of toxicity signs and the difference between seizure treatment and antidote use.

- **Trap:** Waiting for respiratory arrest before acting. **Correct:** Loss of patellar reflex is the early warning; stop the infusion and check breathing.
- **Trap:** Using calcium gluconate to treat eclamptic seizures. **Correct:** Calcium gluconate is the antidote for toxicity, not a treatment for eclampsia.
- **Trap:** Continuing magnesium without checking urine output. **Correct:** Falling urine output suggests renal impairment and accumulation, so dosing is reviewed.

## Frequently asked questions

### What is the antidote for magnesium sulphate toxicity?

Calcium gluconate is the antidote for magnesium sulphate toxicity. An intravenous dose of 1 g of 10% calcium gluconate given slowly reverses the respiratory and cardiac effects. Magnesium sulphate toxicity is treated first by stopping the infusion and supporting ventilation.

### Which sign appears first in magnesium sulphate toxicity?

Loss of the patellar reflex is the earliest sign of magnesium sulphate toxicity. Respiratory depression follows, and cardiac arrest is the late stage. Checking knee jerks before each dose is standard practice in every regimen.

### What is the therapeutic serum magnesium level?

The therapeutic range for magnesium sulphate in eclampsia is commonly quoted as about 4.8 to 8.4 mg/dL. Serum levels are not measured routinely in every patient. They are used when toxicity is suspected or renal function is impaired.

### How long is magnesium continued after an eclamptic seizure?

Magnesium sulphate is usually continued for about 24 hours after delivery or after the last seizure, depending on protocol. Some regimens continue longer in severe disease. Duration follows institutional protocol, and 24 hours is the standard answer in exams.