Pharmaceutical compositions and single unit dosage forms of (+)-2-[l-(3-ethox 4-mcthoxy-phcnyl)-2-mcthancsulfonyl-cthyl]-4-acctylaminoisoindolinc-l,3-dionc, or a pharmaceutically acceptable stereoisomer, prodrug, salt, solvate, hydrate, or clathrate 5 thereof, are provided herein. Also provided are methods of treating, managing, or preventing various diseases or disorders. The compound is known as Apremilast and has the following structural formula: