Sick day rules: which medicines to pause, and why

When someone is unwell and dehydrated, a few common medicines can do harm. Sick day rules tell them which to pause and when to restart. Learn the reason for each medicine, because the reason is what questions test.

What sick day rules are

CKS, the clinical knowledge summaries from NICE, tells clinicians to give adults with type 2 diabetes clear, individual advice on "sick-day rules" for illness. The advice is to temporarily stop some drug treatments during acute illness. The same idea applies to people who take some of these medicines for other reasons, such as blood pressure.

Patient information on the NHS website gives the same trigger for three of these medicines. These are exact quotations.

• Metformin: "If you get ill with vomiting, diarrhoea or a high temperature (fever) when taking metformin, there's a risk you'll get dehydrated. Talk to a pharmacist or doctor for advice, or follow the advice they've already given you." Information from the NHS website, as at 221026.
• Dapagliflozin: "If you get ill with vomiting, diarrhoea or a high temperature (fever) when taking dapagliflozin, there's a risk you'll get dehydrated. Talk to a pharmacist or doctor for advice, or follow the advice they've already given you." Information from the NHS website, as at 221026.
• Ramipril: "Contact your doctor if you get ill while taking ramipril with symptoms such as:" "a high temperature", "sweating and shaking" and "being sick (vomiting) or severe diarrhoea". Information from the NHS website, as at 221026.

The medicines, and the reason for each

This is the CKS list for adults with type 2 diabetes. Each line gives the medicine, the action and the reason.

• ACE inhibitors, angiotensin II receptor antagonists, diuretics and NSAIDs: stop if there is a risk of dehydration, to reduce the risk of acute kidney injury (AKI).
• Metformin: stop if there is a risk of dehydration, to reduce the risk of lactic acidosis.
• SGLT-2 inhibitors: check for ketones and stop treatment if acutely unwell or at risk of dehydration, because of the risk of euglycaemic diabetic ketoacidosis (DKA). Euglycaemic means the blood glucose can look normal or near normal.
• GLP-1 receptor agonists: stop if there is a risk of dehydration, to reduce the risk of AKI.
• Sulfonylureas: they may increase the risk of hypoglycaemia, particularly if dietary intake is reduced.
• Insulin: not stopped. CKS advises that the dose may need altering during illness, and to seek advice from the specialist diabetes team if there is uncertainty on how to adjust it.

Restarting

CKS says medication may be restarted once the person is feeling better and eating and drinking normally for 24 to 48 hours, unless there is concern about renal function. Kidney function is the exception CKS flags, so a person with a kidney concern needs advice before restarting.

On restarting, the ramipril page says: "They may advise you stop taking ramipril until you feel better and are eating and drinking normally." Information from the NHS website, as at 221026.

Monitoring and when to seek help

• Someone using self-monitoring of glucose (for example, on insulin) may need to test more often, such as at least every 3 to 4 hours including through the night, and record the results.
• Where ketone monitoring is needed, CKS gives the same interval, at least every 3 to 4 hours including through the night.
• If the urine ketone level is greater than 2+, or the blood ketone level is greater than 3 mmol/L, the person should seek immediate medical advice.
• CKS says to arrange hospital admission when there is an immediate risk of DKA, such as moderate ketonuria (2+) or ketonaemia (1.5 to 2.9 mmol/L) with the person unable to eat or drink, or suspected AKI that cannot be managed in primary care.

Worked scenarios

At the counter

• Ask what the person takes, including over-the-counter NSAIDs. NSAIDs are on the list.
• Explain the reason for each pause in a sentence, not just "stop these".
• Do not tell them to stop insulin.
• Tell them when to restart, and what to do if they cannot eat or drink.
• Refer when the person is very unwell, the illness is not settling, or ketones are raised.

This guide covers adults with type 2 diabetes only, following CKS. The extended matching questions guide has a practice set built on this topic.

Sources

• NICE CKS: Diabetes - type 2, management (managing intercurrent illness; sick-day rules). https://cks.nice.org.uk/topics/diabetes-type-2/management/management-adults/. Accessed 22 October 2026.
• NHS: How and when to take metformin. https://www.nhs.uk/medicines/metformin/how-and-when-to-take-metformin/. Accessed 22 October 2026.
• NHS: How and when to take dapagliflozin. https://www.nhs.uk/medicines/dapagliflozin/how-and-when-to-take-dapagliflozin/. Accessed 22 October 2026.
• NHS: How and when to take ramipril. https://www.nhs.uk/medicines/ramipril/how-and-when-to-take-ramipril/. Accessed 22 October 2026.

Information from the NHS website is licensed under the Open Government Licence v3.0. This covers the three NHS pages above only. The NICE CKS page is separate content and is not covered by that licence.

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Not affiliated with the General Pharmaceutical Council. Revision only, not clinical or legal advice. Worked examples use invented numbers and products. Every source above was read on 22 October 2026; check anything that matters against a current source. See our terms of use and privacy notice.