Busulfan is achemotherapy drug frequently used to prepare children for bone marrow transplantation. In the past, Busulfan was taken by mouth as a pill or, in young children, administered through a soft feeding tube through the nose into the stomach. More recently, an intravenous (IV) preparation of busulfan has become available. Busulfan is used to make space in the marrow to allow donor cells to grow, or engraft.
The problem with the oral form of busulfan is that the rate at which busulfan is absorbed from the stomach into the blood stream varies greatly from child to child. Also, once it enters the blood, the handling of busulfan by the tissues in the body — that is, how busulfan is distributed to the tissues and how it is eliminated from the body — varies considerably from child to child. Both of these factors influence the total amount of busulfan to which the child is exposed. If the total is too little, the graft is rejected; if it is too much, it can cause damage to healthy tissues such as the brain, lungs, liver and kidneys.
Working with doctors from the University of Washington, the UCSF Benioff Children's Hospital Bone Marrow Transplant Program has been studying busulfan for many years in order to learn more about how the drug is absorbed and eliminated in children. Based on our work, we have found busulfan levels in the blood that optimize engraftment while minimizing toxicity.
If your child will be receiving busulfan as part of the conditioning regimen, a pharmacokinetic study will be done either prior to admission for transplant or on the first dose of busulfan following admission. The former evaluation is done as an outpatient in the UCSF Pediatric Clinical Research Center. The busulfan dose is customized for each child to achieve a level that we believe will optimize donor marrow growth and minimize negative side effects. The attending physician will discuss the pharmacokinetic study in more detail at the informed consent conference.
For information on specific disease protocols that utilize busulfan pharmacokinetics, please see marrow stem cell defects and genetic diseases.