If anybody thinks Trump or Dr Zelenko are being original, see this article from April 17. ETA: India began using it on March 23
https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30313-3/fulltextThe Indian Council of Medical Research, under the Ministry of Health and Family Welfare, has recommended chemoprophylaxis with hydroxychloroquine (400 mg twice on day 1, then 400 mg once a week thereafter) for asymptomatic health-care workers treating patients with suspected or confirmed COVID-19, and for asymptomatic household contacts of confirmed cases.2 The document states “its use in prophylaxis is derived from available evidence of benefit as treatment and supported by preclinical data”. Although some in-vitro evidence supports the antiviral activity of hydroxychloroquine and its precursor chloroquine, there is no peer-reviewed publication that evaluates either drug for exposure prophylaxis of SARS-CoV-2 infection. Even for treatment of diagnosed cases, only one small study reported faster nasopharyngeal viral clearance, with no data for clinical improvement.