The Feverish Knee and Three Medicines That Do Not Mix
A 68-year-old man attends a rural sub-centre in Nalbari district with fever for two days and a painful, swollen right knee. His medicine card lists enalapril 10 mg twice daily, furosemide 40 mg each morning and metformin 500 mg twice daily. A creatinine done three months ago was 1.6 mg/dL, with an eGFR of about 40 mL/min/1.73 m². The visiting medical officer, seeing the hot knee, writes diclofenac 50 mg twice daily for five days and reaches for his pen to sign the slip. Today the patient's blood pressure is 104/68 mmHg with a postural drop, pulse 96/min and temperature 38.4 °C. He says he has passed very little urine since morning and feels dizzy when he stands. The health worker holding the slip is a trained nurse with no prescribing rights but a clear view of the notes.
1. What is the most dangerous element of this prescription, and what should the health worker do before the patient leaves the sub-centre?
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The problem is the combination, not the diclofenac alone.
Diclofenac with an ACE inhibitor and a loop diuretic in a volume-depleted older adult is the classic triple whammy. The NSAID blocks prostaglandin-mediated dilation of the afferent arteriole, the ACE inhibitor dilates the efferent arteriole, and the diuretic has already reduced circulating volume. Together they can drop glomerular filtration abruptly. This patient is already at the edge: an eGFR near 40, oliguria since morning, postural dizziness and a systolic pressure of 104 mmHg are signs of dehydration, not just fever. Metformin adds a second hazard: if renal function falls, metformin accumulates and lactic acidosis becomes possible.
Before he leaves:
- Do not dispense. Raise the concern with the medical officer before the slip is signed.
- Assess hydration: mucous membranes, skin turgor, capillary refill, urine colour and volume, weight if possible, and lying and standing blood pressure.
- Suggest paracetamol 500 to 1000 mg, maximum 3 g a day in an older adult, and ask the officer to look again at the knee. Fever with a hot joint may be septic arthritis, which an NSAID would only mask.
- Apply sick-day rules: hold metformin and consider holding enalapril and furosemide while he is dehydrated, with clear instructions on when to restart.
- Send a urine sample and arrange creatinine and potassium.
- Record the discussion, the advice given and the plan, including who was informed and what was decided.
2. The medical officer says one short course of diclofenac will not hurt. How would you argue the case using this patient's numbers, and what monitoring would make any NSAID use safer?
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Argue with the numbers, not with opinion.
- eGFR about 40 mL/min/1.73 m²: NSAIDs are generally avoided below 60 and contraindicated below 30. He is already in the caution zone.
- Systolic 104 mmHg with a postural drop and oliguria: acute volume depletion is exactly when NSAID-related acute kidney injury is most likely.
- Age 68, fever and poor oral intake add to the risk.
- Two concurrent drugs that already act on glomerular haemodynamics.
- Metformin on board: a fall in eGFR turns a safe drug into a lactic acidosis risk.
- Gastrointestinal risk: NSAID plus age over 65 raises bleeding risk even without aspirin.
A short course is precisely how most NSAID-related kidney injury presents in practice, so duration is not a reassurance. A safer plan is paracetamol, topical diclofenac gel if only the joint is involved, and treatment of the cause of the fever.
If the officer still prescribes an NSAID: rehydrate first, use the lowest dose for the shortest time, hold the diuretic and ACE inhibitor during the illness, warn the patient to stop and return if urine output falls or dizziness worsens, and recheck creatinine and potassium within three to five days. Record the decision and the monitoring plan in the card.
3. Write the counselling you would give the patient and his family, and list what goes into the record.
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Explain in plain language that fits his level of understanding. For example: your kidneys are working with less reserve, and this painkiller can shut them down when your body is dry from fever. We are giving a safer medicine and asking you to sip fluids.
Specific advice:
- Take paracetamol exactly as directed and no more than 3 g in a day.
- Sip oral fluids in small, frequent amounts rather than large volumes at once.
- Restart the regular medicines only when eating and drinking normally again, and only as advised by the medical officer.
- Danger signs that mean return at once: no urine for 8 to 12 hours, dizziness on standing, vomiting everything, confusion, fast breathing, or a knee that becomes hotter and more swollen.
- Return in 48 to 72 hours with the creatinine and potassium reports.
In the record: blood pressure lying and standing, temperature, hydration findings, the fact that diclofenac was not dispensed and why, the alternative given, the sick-day instructions, the investigations ordered, the review date, and the medical officer's final decision. If the patient later develops kidney injury, this note is the evidence that the risk was recognised and acted on.