A 60-year-old cancer patient developed a black, hairy tongue as a side effect of an antibiotic that was prescribed to her to counter some of the effects of chemotherapy.

The patient was taking minocycline, a prescription medication commonly used to treat various bacterial infections, including urinary tract infections, skin infections, severe acne, tick fever and chlamydia. It is also given to patients with gonorrhea and syphilis and those who are allergic to penicillin.

The drug has its own array of complications, including blood in the urine or stools, blurred or double vision, hives, itching, or skin rash, sores and ulcers in many body regions. However, what the woman suffered is an uncommon but known side effect of minocycline.

According to a report published in the British Medical Journal Case Reports, the woman was taking minocycline to prevent skin lesions caused by chemotherapy. After some time, she developed dark patches on her face and a black, hairy tongue – a condition called drug-induced hyperpigmentation and black hairy tongue. Her tongue was covered in patches that were brownish-black in appearance and caused pain.

Doctors said the grey patches on her face were another potential side effect of the antibiotic. Her symptoms improved when she stopped taking the medication.

What is the science behind the condition?

Black hairy tongue (BHT) is a condition where the filiform papillae (thread-like structure on the tongue's surface) become elongated and hypertrophied, resulting in black or brown discoloration, which may cover 3% to 15% of the tongue's surface area.

To treat the minocycline-induced skin pigmentation, the woman underwent a trifluridine and tipiracil hydrochloride plus bevacizumab combination therapy, the report said. She was back to normal in six weeks.

The condition isn't typically harmful but is a sign that a person has poor oral health. The medics were sure that minocycline was to blame in this case.

The woman was battling rectal cancer and was put on chemotherapy 14 months earlier. Minocycline was prescribed to her after she developed skin lesions as a side effect of the chemotherapy.

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