Pharmacokinetic Studies Participation Survey

Background: * A pharmacokinetic (PK) study of a new drug involves taking several blood samples over a period of time from study participants to determine how the body handles the substance. These studies provide critical information about new drugs. * Often, patients or parents of children in drug studies choose not to participate in optional PK studies that are part of the study protocol. * A better understanding of why patients or families do or do not agree to participate in PK studies may help researchers make it easier for people to participate in them. Objectives: * To learn why some people do or do not agree to participate in PK blood sampling studies. Eligibility: * Patients 18 years of age and older and parents or guardians of children who are participating in a study of a drug that includes the option of participating in PK sampling. Design: * Participants fill out a 2-page survey asking about why they did or did not participate in the study's PK sampling.