Tapering quetiapine (my first question here)

Hi, My first post/question on this forum. My son restarted his quetiapine taper 1 month ago. He came from 600 mg three years ago. He suffered PWS for one year I guess (my son's doctor for mentally handicapped does not have much knowledge about tapering). He has a lot of problems from the quetiapine like dystonia/dyskinesia. We microtapered one pill of 6,25 mg by microtapering with suspension, 2,5 ml in parst of 0,1 ml a day. That is 7,6 % in 25 days. Is there anything at all one can say about how long it will take to reach 0 mg? Are there known ranges (below 25 mg?) where one has to go below in my case that 7,6 %? Or areas where one can go a little faster (below say 2 mg?) Following a scheme with 7,6 % all the time would cost almost 6 years (see below my sig), without stabilisation periods. Kind regards, Stefan. Invoergegevens: Startdosis: 75,00 mg Afstappen bij: 0,2000 mg Interval: 4 weken Reductiepercentage per interval: 7,7 Aantal significante getallen: 4 Berekend: Totale duur: 5 jaar(en) en 36 week(en) Schema: Weken Dosis (mg) 0 75,00 4 69,23 8 63,90 12 58,98 16 54,44 20 50,25 24 46,38 28 42,81 32 39,51 36 36,47 40 33,66 44 31,07 48 28,68 52 26,47 56 24,43 60 22,55 64 20,81 68 19,21 72 17,73 76 16,36 80 15,10 84 13,94 88 12,87 92 11,88 96 10,97 100 10,13 104 9,350 108 8,630 112 7,965 116 7,352 120 6,786 124 6,263 128 5,781 132 5,336 136 4,925 140 4,546 144 4,196 148 3,873 152 3,575 156 3,300 160 3,046 164 2,811 168 2,595 172 2,395 176 2,211 180 2,041 184 1,884 188 1,739 192 1,605 196 1,481 200 1,367 204 1,262 208 1,165 212 1,075 216 0,9922 220 0,9158 224 0,8453 228 0,7802 232 0,7201 236 0,6647 240 0,6135 244 0,5663 248 0,5227 252 0,4825 256 0,4453 260 0,4110 264 0,3794 268 0,3502 272 0,3232 276 0,2983 280 0,2753 284 0,2541 288 0,2345 292 0,2164 296 0,1997