This study will evaluate a three drug regimen in the form of two pills which will be taken for 28 days for the prevention of HIV infection. Two drugs are combined in an FDA-approved pill called TRUVADA, containing the HIV medications, tenofovir disoproxil fumarate 300mg and emtricitabine 200mg, taken as one pill once a day. The third drug is a new formulation, raltegravir 400mg pill taken twice a day.