I've never had a serious case of hole in the head disease so I'm not really in a position to recommend treatments on experience. However, any treatment is worth trying if your fish have the disease. Before you do any treatment, try and address why your fish may have developed this disease. It is your water in good condition? What type of food you feed it? Its not worth starting any treatment unless your tank water is an extremely good condition. What are your water readings, ammonia, nitrite, nitrate and pH? Anyway, I googled the treatment he mentions and came up with a few websites, I chose the first one. It is worth mentioning that in some cases, hole in the head disease can be cleared up by a regular and increase tank maintenance, i.e. regular water changes. Obviously severe cases will need treatment.
http://www.eshalabs.com/hexamita.htm