A Phase I Study to Assess the Pharmacokinetics of Metformin When Administered Alone and in Combination With Vandetanib

Inclusion Criteria: * Healthy males or females aged 18 to 50 years with a weight of at least 50 kg and a body mass index between 18 and 30 kg/m2 inclusive. * Females must have a negative pregnancy test at screening, must not be lactating and must be of non-childbearing potential. * Volunteers will be wild type for the OCT2 gene (as tested for within the last 6 months prior to Day 1 in Period 1) Exclusion Criteria: * History or presence of gastrointestinal, hepatic, or renal disease or any medically significant disorder. * History of or ongoing severe allergy/hypersensitivity to drugs with a similar chemical structure or class to vandetanib or metformin. * Volunteers who smoke more than 5 cigarettes per day or are unable to refrain from smoking while resident in the study center. * Known or suspected history of drug abuse. * Screening supine blood pressure of greater than 140/90 mmHg and/or a resting heart rate of less than 45 beats per minute. * Clinically significant current active skin disease (eg moderate to severe acne, psoriasis, eczema). * Any positive result on screening for serum hepatitis B, surface antigen, hepatitis C antibody, and human immunodeficiency virus (HIV).