Comparative Bioavailability in Healthy Elderly Volunteers

Inclusion Criteria: * Male and female 55 and over * No clinically important abnormal physical finding * No clinically significant lab results * Normal ECG, Normal BP and HR,BMI between 19 and 32 * Weight 50 to 100 kg, Able to communicate * Provide written informed consent * Non smokers * Males to use contraception * Females to be surgically sterile or post menopausal Exclusion Criteria: * Administration of any IMP other than study drug within 12 weeks before entry * Use of any prescribed meds, St John's wort, over the counter meds as described in the protocol * Surgical or medical condition that might interfere with IMP * History of drug or alcohol abuse * Clinically significant allergy requiring treatment * Loss of greater than 400ml of blood within 12 weeks. * Serious adverse reaction or hypersensitivity to any drug * Prescence of Hep B, Hep c or HIV-1 or HIV-2 at screening * Presence of G6PD at screening * History of methaemoglobinaemia * Partner who is pregnant of lactating * Positive Pregnancy test