It seems the first the PJ heard about sedation was three months after Madeleine disappeared.
3rd September 2007 Ricardo Paiva.
Strangely, Kate also made several requests, three months after the disappearance of Madeleine, that the police should take blood, hair and nail tests of Madeleine's twin siblings, because, as she said, she remembered that on the day of Madeleine's disappearance, in spite of all the commotion and noise made by the authorities and other persons who were looking for Madeleine in apartment 5A of the OC, the twins never woke up, having been transported to another apartment, they remained asleep, due to which she now presumes that they were under the effect of some sedative drug that a presumed abductor had administered to the three children in order to be able to abduct Madeleine, a situation which Kate refers to being possible according to what she read in a criminal investigation manual given to her by the British authorities, that would have been the procedure of the abductor in the real case involving abduction, rape and murder of the girl.
http://www.mccannpjfiles.co.uk/PJ/SERVICE_INFORMATION.htm