Implantable devices for controlled delivery of a drug are provided which include a substrate; at least two reservoirs in the substrate, each reservoir having an opening; at least one therapeutic agent in each of the reservoirs; a reservoir cap sealing each opening; a mechanical rupturing mechanism which moves into contact with and ruptures the reservoir cap to permit release the therapeutic agent from the reservoir through the opening; and a mixing chamber adjacent the reservoirs, wherein upon release of the therapeutic agent from at least one of the reservoirs, the therapeutic agent is combined with a carrier fluid in the mixing chamber and then transported to a delivery site in a human or animal.