Micromedex® includes two drug information apps - Micromedex® Drug Reference for Internet Subscribers, Micromedex® Drug Interactions.
UpToDate® drug information includes
ClinicalKey's Drug Monographs provides access to drug information from Gold Standard Drug Database with information including specific drugs, dug class, adverse reactions, pharmacokinetics, contraindications etc.
Epocrates Rx is the free App that allows you to access drug information, interaction checker, pill ID, calculators etc.
National Library of Medicine Drug Information Portal