TB drug affects vision in some patients

Over the last three years, from January 2013 to April 2016, 86 drug-resistant TB patients were observed for eye complaints, as a result of consuming a potent anti-TB drug—Linezolid in the study. All the patients were between 20–35 years. Of the 86, 24 of them had at least one episode of eye-complaint while five of the patients studied, developed complications of 'Optic Neuropathy.'

Doctors say that the reason Linezolid can be dangerous is because it has a direct toxic effect on the neurons. Explaining how this affects vision, Dr Salil Mehta, ophthalmologist, Lilavati Hospital and co-author of the study says, "There are a million of them (neurons) in the retina of the eye. They join together to build a tube called 'Optic Nerve,' that connects to the brain and send electrical transmissions which forms vision."

The study speaks of the case of a 23-year-old woman on Linezolid, who complained of blurred vision in both eyes. A few days prior to eye-related complaints, she had pain and difficulty in walking. After tests were conducted, it was revealed that her optic nerve had become swollen.

"Linezolid was discontinued presumptively for the patient for up to ten weeks and she was put on medication to cure the eye. Eventually, she recovered, and was started on Linezolid treatment again," said Dr Mehta.

He added, "Other patients were examined by doctors after 10 to 15 days of them complaining about vision problems, after taking the drug. "We immediately stopped using Linezolid in such cases and started them on steroids to reduce inflammation inside the eye. All patients recovered within one and a half to three months."

The reason doctors have been using Linezolid is because it is considered to be useful in treating drug-resistant TB (DR-TB). DR-TB is a condition in which patients who were put on first-line treatment for TB have failed it and developed resistance to basic drugs like Rifampacin, Isoniazid and Ethambutol, which are the first drugs used to treat TB.

The patients also then developed resistance to fluoroquinolones, which are key components of current multidrug-resistant tuberculosis (MDR-TB) treatment regimens, as well as injectable anti-TB drugs. Such patients become multidrug-resistant (MDR) as well as extensively drug-resistant (XDR). With each progression, it becomes more difficult to find drugs that will work on patients.

India has to be especially conscious of this problem. Of the 96 lakh TB patients in the world, the country houses 22 lakh patients. Doctors say, as Linezolid will be increasingly added to treatment regimens of DR-TB patients around the world, regular eye screening may help in early identification and treatment of patients with Linezolid-associated neuropathy.

The World Health Organization estimates that India has 75,000 multidrug-resistant TB cases, of which up to 2%, at least 1,500 patients, will go on to become pre-XDR and XDR-TB cases, who require newer drug-regimens for potential cure.

"It is a double-edged sword. On the one hand, you want to save the patient from life-threatening TB, on the other, the patient runs the risk of losing his vision. We are fortunately able to detect the adverse effects of the drugs early. But if not tracked early, toxicity can adversely affect the body, possibly leading to a permanent loss of vision," said Dr Mehta.

He adds "However, if used under proper monitoring and supervision, Linezolid is an excellent anti-TB drug."

Attacking the eyes

• Anti-TB drug—Linezolid has affected the vision of patients
• Study on 86 patients showed 24 of them developed eye problems
• Once vision gets affected, patients have to be weaned off 'Linezolid'
• Condition of blurring vision is reversible, if detected, and treated early

Source: DNA India