I'm the mother of an 8th year old boy diagnosed with DS at the age of 4. Since then he has been on stiripentol, Sodium Valproate and Clobazam, which are considered until now the very best drugs to use in DS. He has a tremendous development delay. We also tried alternative medicines, which helped but you should be very carefull as well as with the allopatic medicine becouse there are many drugs and substances that do interfer with AED's eficacity but specially with stiripentol.
I advise you to contact Idea League http://www.idea-league.org,
the onliest world organisation focused on DS. They have a world of information regarding DS as well as on terapies. They do can help you.
The very best doctors specialised on this problem are prof. Renzo Guerrini; Prof. Charlote Dravet; Prof. catherine Chiron; Prof. Olivier Du Lac; Dr. Nabout; Dr. Douglas Nordli. You can contact them by e-mail. Their contacts are available in the internet.