High-risk drugs

Why this matters on day one

A small number of drugs account for a disproportionate share of severe incidents. Knowing which ones demand a second look — and what specifically goes wrong with each — is more protective than any general caution.

The sequence

1. 1Anticoagulants. Confirm the indication, the target and the monitoring. Warfarin: INR, interactions (antibiotics, amiodarone, NSAIDs), and vitamin K consistency in diet. DOACs: renal dose adjustment, and no routine monitoring — which means no safety net either. Always ask about bleeding and about upcoming procedures.
2. 2Insulin. Never abbreviate units. Prescribe by brand name (insulin preparations are not interchangeable). Know the regimen and whether the patient self-administers. Never omit long-acting insulin in type 1 diabetes, even when nil by mouth — that causes DKA.
3. 3Opioids. Start low in the elderly and in renal impairment. Prescribe an aperient with every opioid. Know your equivalences before converting route or drug, and check with pharmacy if unsure. Naloxone available for respiratory depression.
4. 4Potassium. Never as an undiluted bolus. Peripheral infusion no faster than 10 mmol/hour; faster needs cardiac monitoring and central access. Recheck U&E after replacement, and correct magnesium too or the potassium will not stay up.
5. 5Methotrexate. WEEKLY, not daily — daily dosing has killed patients. Folic acid on a different day. Monitor FBC, LFT and renal function. Avoid trimethoprim (both are antifolates).
6. 6Lithium and gentamicin. Both need levels and both have a narrow therapeutic index. Lithium: level 12 hours post-dose, watch NSAIDs, ACE inhibitors, diuretics and dehydration. Gentamicin: dose by weight and renal function, level at the specified time, and stop if renal function deteriorates.

What goes wrong

• Methotrexate prescribed daily. Check the frequency twice, every time.
• Omitting basal insulin because the patient is fasting.
• "Units" abbreviated to "U" and misread as a zero.
• Converting opioid routes from memory — oral to subcutaneous morphine is not one-to-one.
• Prescribing an NSAID on top of an ACE inhibitor and a diuretic (the "triple whammy" for AKI).