Raltegravir (Isentress) Pilot Study in Relapsing Multiple Sclerosis

Inclusion Criteria: * Patients between 18-55 years of age. * Diagnosis of MS, according to the revised McDonald Criteria 2010. * EDSS score of 0-6.0 inclusive. * Documented at least one relapse within the past 12 months or at least one Gd-enhanced lesion on the brain MRI detected within 3 months prior to screening date * Gd-enhanced lesion on screening MRI (if MRI not used to meet screening criteria above). * Female patients of childbearing potential will be expected to be on appropriate contraception (hormonal or barrier method of birth control; abstinence) from time of consent until 6 weeks after treatment discontinuation. (the repeated administration of gadolinium and MRI are not recommended during pregnancy). NOTE: Subjects are considered not of child bearing potential if they are surgically sterile (they have undergone a hysterectomy, bilateral tubal ligation, or bilateral oophorectomy) or they are postmenopausal. * Females of childbearing potential must have a negative urine pregnancy test prior to every MRI scan/ within 7 days prior to being registered for protocol therapy. * Must give written informed consent and authorize the release and use of protected health information, as required by local law. * Able and willing to undergo blood, saliva and urine sampling at regular intervals as defined by the protocol. * Able and willing to receive Gadolinium enhanced MRI's at regular intervals as defined by the protocol. * Able to comply with study requirements. Exclusion Criteria: * Pregnant or breastfeeding or unwilling to use contraception. * Treatment with immunosuppressive, immunomodulatory or experimental treatments within the last 6 months of enrolment in the study, but excluding pulsed intravenous or oral steroids for treatment of MS relapse. * No pulsed intravenous or oral steroids in the 30 days preceding the baseline assessment. * Patients presenting with medical disorder deemed severe or unstable by the CI such as poorly controlled diabetes or arterial hypertension, severe cardiac insufficiency, unstable ischemic heart disease, abnormal liver function tests (\>2.5 times ULN) and abnormal complete blood count (in particular leukopenia, as defined by a lymphocyte count \<500, neutrophil \<1.5 or platelet count \< 100, or thrombocytopenia \< 1.5 LLN), or any medical condition which, in the opinion of the chief investigator, would pose additional risk to the patient. * Presence of human immunodeficiency virus antibodies. * Patients receiving proton pump inhibitors (e.g. omeprazole/esomeprazole) * Patients with active hepatitis B or/and C with liver function tests \>2.5 times ULN * Exposure to any other investigational drug within 30 days of enrolment in the study. * Prior history of malignancy unless an exception is granted by the Chief Investigator. * History of uncontrolled drug or alcohol abuse within 6 months prior to enrolment into the study. * Patients treated with Rifampicin in past four weeks.