An adapter includes a housing having an inlet port defining a flow path and an outlet port. An interior wall has an inner surface defining an interior passageway communicating with the outlet port and an exterior surface defining an exterior passageway communicating with the inlet port. The interior wall defines a mouth communicating between the interior and the exterior passageways. The interior wall is positioned transverse to the flow path of the inlet port. A medicament delivery port opens into the mouth. A valve is moveable between a closed position, wherein the valve closes the medicament delivery port, and an open position, wherein the medicament delivery port is open. A ventilator circuit and method of delivering a medicament are also provided.