Published: 4 June 2020


Alerting the Medical Warning System can save lives!

Prescriber Update 41(2): 29–30
June 2020

Key Messages

  • The Medical Warning System (MWS) is used to alert health care professionals in district health board secondary care that a particular patient has had a previous serious adverse drug reaction. This can save lives.
  • It is important to inform the Centre for Adverse Reactions Monitoring of these life-threatening reactions as they can update the MWS for that patient.


Recently the Centre for Adverse Reactions Monitoring (CARM) received a case report in which a patient died after treatment with an antibiotic. Investigation into the patient’s history showed that earlier the patient had experienced an anaphylactic reaction to the same medicine at a different treatment centre. However, this information was not recorded in the Medical Warning System (MWS), and the anaphylactic reaction had not been reported to CARM.

The Medical Warning System

The MWS is a national alert service linked to the National Health Index (NHI) numbers1. The MWS alerts health care professionals to known risk factors that could be important when making clinical decisions about patient care. This includes information on serious and/or life-threatening adverse reactions to medicines, such as anaphylaxis.

The MWS system is currently visible to the district health boards (DHBs), but not to primary care. In some areas, however, general practitioners (GPs) can access the information via their DHB. Although GPs may also add a medicine allergy alert in their Patient Management System (PMS), this alert is only visible to their practice and is not automatically added to the MWS. Opportunities to make the MWS more accessible to primary care are under consideration.

Adding an alert

There are two types of medicine alerts: Danger and Warning.

  • A Danger alert reflects a contraindication to further use for the patient. Used, for example, when the patient has had an anaphylactic-type reaction or any other life-threatening reaction.
  • A Warning alert indicates that the medicine has caused the patient significant morbidity and should be avoided. Some alerts need to be qualified, for example, “tolerates at slow infusion rate”.

CARM adds many of the medicine alerts to the MWS. The alerts are generated from adverse drug reaction (ADR) reports sent to them from health care professionals and the public. When CARM receives an ADR report, the medical team assess the case and, based on the nature of the event, may place a Danger or Warning alert on the MWS for the medicine, listing the associated reaction(s). Some hospitals/DHBs have systems in place and designated staff who enter Warning alerts into the MWS, but only CARM can place a Danger alert.

CARM receives approximately 4,000–5,000 ADR reports per year. Of these, about 1,500 are vaccine-related and only occasionally require an entry on the MWS. Of the remaining reports, about 2,500 are for therapeutic medicines and result in approximately 500 Danger entries and 1,000 Warning entries on the MWS.

ADR reporting is vital

Reporting adverse drug reactions is vital so that where necessary, CARM can add an alert to the MWS. Whenever the patient's NHI is accessed in the future, details of the alert (Danger or Warning) are available to health care professionals who can access the MWS. This is crucial in patients who are not able to speak for themselves, are confused or may have forgotten an event from distant history. The MWS alert may also be more reliable than asking the patient, especially when health literacy is low, or there are language barriers.

ADR reporting is easiest online.


  1. Ministry of Health. 2019. Medical Warning System 13 February 2019. URL: (accessed 15 April 2020).
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