hydroxychloroquine, once touted by Donald Trump as a pandemic "game-changer", should not be used to prevent COVID-19 and has no meaningful effect on patients already infected, a World Health Organization expert panel said on Tuesday.The anti-inflammatory drug should not be used in the fight against the pandemic, the WHO's Guideline Development Group (GDG) expert panel wrote in the BMJ British medical journal, and is "not worthwhile" exploring in further research studies of possible COVID-19 treatments.This "strong recommendation", the experts said, is based on high-certainty evidence from six randomised controlled trials involving more than 6,000 participants both with and without known exposure to COVID-19.Former U.S.