Hydroxyurea
"I am 80 years and have been taking this drug for 7 years without problems, it kept my platelets around 600,000. Then I developed open sores on my fingers. A blister would form, pop, and then the sore would be exposed and wouldn't heal for weeks. After that I developed wounds on my ankles. I developed  3 open, non-healing ulcers on my ankles that were so painful I had to go to the hospital. All the while my hematologist, my primary doctor and all the hospital doctors shook their heads and said they didn't know what was wrong. Then my son did a google search and found that these horrible skin ulcers and sores were a rare side effect of the hydroxyurea! I am now off the drug and with a new hematologist and a new drug Jakafi."