Clinical Pearl: The "Technicolour" Side Effects of Pharmacology
Recognising them prevents unnecessary workups and allows for proactive patient counselling.
While we typically monitor for invisible pharmacokinetic changes, some medications announce their presence vividly by altering the colour of biological fluids and tissues. These "technicolour" side effects can be alarming for patients but are often benign. Recognising them prevents unnecessary workups and allows for proactive patient counselling.
1. Urine Discolouration (The Most Common)
Red / Orange:
- Rifampicin: Causes orange-red urine (and tears/sweat).
- Phenazopyridine: Distinctive orange urine.
- Senna Glycosides & Dantron Laxatives: Can turn urine red-brown.
Blue / Green:
- Propofol: Green urine.
- Amitriptyline: Blue-green urine.
- Methylene Blue: Blue-green urine.
Brown / Black:
- Metronidazole: Red-brown to dark urine.
- Levodopa/Methyldopa: Darkens on standing.
2. Skin and Sclera Pigmentation
Blue-Gray ("Ceruloderma"):
- Amiodarone: Causes a blue-grey discolouration in sun-exposed areas.
- Minocycline: Can cause blue-black pigmentation on the shins, scars, or the sclera.
Red-Brown / Violet:
- Clofazimine: Causes a reddish-brown to violet skin discolouration ("leprosy dye").
Yellow:
- Sunitinib: Can cause a yellowish skin hue (distinct from jaundice).
3. Mouth, Teeth & Hair
"Black Hairy Tongue":
- Bismuth Subcitrate: Turns tongue (and stool) black.
Teeth Staining:
- Tetracyclines (Doxycycline/Tetracycline): Permanent gray-brown staining in children <8 years.
Hair Colour Changes:
- Chloroquine: Can bleach hair (depigmentation) to a silver/white colour.
- Sunitinib: Can cause reversible hair depigmentation (white hair growing during treatment cycles).
Clinical Takeaway
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Counsel before you prescribe: Always warn patients about these changes before they happen.
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Contact lenses: Patients on rifampicin should avoid soft contact lenses as they will be permanently stained orange.
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Urinalysis interference: Dyes like phenazopyridine and methylene blue can interfere with colourimetric urinalysis dipsticks (e.g., false positives for protein or glucose).
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Benign vs. Pathologic: Reassure patients that bismuth-induced black stool is not melena, and metronidazole-induced dark urine is not haematuria or rhabdomyolysis.