Drug maker Merck & Co. says that slow going in the testing of an experimental insomnia drug it has been touting for more than a year will delay plans to seek federal approval to sell the medicine.

Gaboxadol, which would be the first of a new class of sleeping pills, is being jointly developed by Whitehouse Station-based Merck and H. Lundbeck A/S, a Danish drug company that specializes in medications for psychiatric and neurological disorders.