What factors should influence the dosage and interval of prophylactic treatment in patients with severe haemophilia A and B?

In order to prevent arthropathy, prophylaxis has to start at a young age before recurrent joint bleedings have taken place. The use of central venous lines has facilitated an early beginning to treatment, but due to side-effects, most European paediatricians prefer peripheral injections whenever possible. By starting primary prophylaxis at the age of 1--2 years with one injection weekly, the need for surgical implants may be reduced. In this study, only four of 34 boys born 1988--98 with severe haemophilia A or B needed a Port-a-Cath for primary prophylaxis. Trough levels were measured in these patients and 79% showed a trough level < 1%, while 21% reached a level > 1%. Despite this, joint bleedings during 1998 were rare in both groups [0--4] and 59% of the boys with trough levels < 1% did not report any haemartroses during that year. Mean annual joint bleedings were the same in both groups [0.70, 0.71]. The lowest effective level of factors VIII and IX must be determined individually for each patient on primary or secondary prophylaxis.