Effectiveness of Calcium Channel Blockade for OP and Carbamate Pesticide Poisoning

Inclusion Criteria: * Patients aged 16 years or older with suspected OP or carbamate insecticide self-poisoning admitted to medical wards with the cholinergic toxidrome requiring atropine. * Diagnosis will be made on the basis of the cholinergic toxidrome clinical features (eg. small/pinpoint pupils, bronchorrhoea, sweating) or on the history of atropine administration with beneficial effect. The insecticide involved will be identified where possible from the history, the bottle brought in by the patient or relative, the patient/relative identifying the pesticide on a chart showing all locally available pesticides, and/or relatives sending a photo of the bottle by eg. WhatsApp. * Patients who ingest combination products containing OP or carbamate insecticides will also be included. * Inhibited blood cholinesterase activity as shown by routine clinical bedside test Exclusion Criteria: * Children aged \<16 years. * Patients who do not require atropine and have not had it prior to presentation during this episode. * Normal blood cholinesterase activity * Self-reported known pregnancy (as per South Asian practice, no attempt will be made to formally test for pregnancy in the patients due to the issue of confidentiality in the acute care situation in these hospitals and the social consequences of an unexpected positive response) * Known occupational and homicidal poisoning * Past medical history of severely impaired renal function * Hypersensitivity to magnesium and its salts * Patients who have had a myocardial infarction or unstable angina in the last month * Patients with traumatic subarachnoid haemorrhage * Lack of informed consent (unaccompanied unconscious patients and others)