Douma incident was a propaganda stunt orchestrated by the Western-backed White Helmets, which have time and again liaised with terrorist groups for information warfare.
No evidence given. Recurring pro-Kremlin disinformation on White Helmets and chemical attacks in Syria. euvsdisinfo.eu/disinformation-cases/?text=&disinfo_issue=&disinfo_keywords%5B%5D=77488&date= euvsdisinfo.eu/disinformation-cases/?text=syria&disinfo_issue=&disinfo_keywords%5B%5D=77353&date=
Earlier, pro-Kremlin disinformation has claimed that both the 2017 attack in Khan Sheikhoun and 2018 in Douma were faked. UN-OPCW Joint Investigative Mechanism found Syria’s Government responsible for last year’s attack in Khan Shaykhun. On April 10 2018 Russia vetoed a U.S.-drafted U.N. Security Council resolution that would have created a new inquiry to ascertain responsibility for chemical weapons attacks in Syria.
On 7 April 2018, a high number of civilians were killed in the besieged Syrian city of Douma, with evidence pointing towards another chemical attack by the regime, according to the EU.
According to the World Health Organisation, during the shelling of Douma on Saturday, an estimated 500 patients presented to health facilities exhibiting signs and symptoms consistent with exposure to toxic chemicals. http://www.who.int/mediacentre/news/statements/2018/chemical-attacks-syria/en/
See also Bellingcat's open source survey on the suspected chemical attack: https://www.bellingcat.com/news/mena/2018/04/11/open-source-survey-alleged-chemical-attacks-douma-7th-april-2018/
In September 2017, the UN Commission of Inquiry on the Syrian Arab Republic summarized 33 separate incidents where it had found use of chemical weapons. Since then there have been several additional suspected chemical attacks. Between March 2013 and March 2017, the Commission documented 25 incidents of chemical weapons use in the Syrian Arab Republic, of which 20 were proven to have been perpetrated by government forces and used primarily against civilians.