Andy,
If I remember correctly some of the stuff that I have read on this topic, hydroxy urea only works on a small proportion of people by stimulating an increase in Hb F. But, it has to be administered as a drip intravenously, so you are just substituting one drip for another, and it has its own side effects.
Let me see if I can dig up more data on this.
Cheers
Poirot