For the first time, the FDA has approved a medication specifically to treat new mothers who suffer from postpartum depression.The drug is called Brexanolone and will be sold under the name Zulresso.The drug's maker, Sage Therapeutics, says only one dose is needed. Zulresso is administered in an intravenous drip that takes nearly 60 hours and is expected to cost between $20,000 to $35,000.Clinical trials show it works within hours.Postpartum depression affects about 400,000 American women a year. It's often treated with antidepressants, though they can take several weeks to help and don't always work.