How much did he . swallow? Take the bottle with you if going to the ER. Call them and ask about the antidote or call Poison Control for fast treatment. Make sure afterwards to keep it away and out of the medicine cabinet. So it doesn't happen again. Prevention!
Call Poison Control. Caladryl is an over-the-counter brand that commonly contains camphor which may be harmful if ingested (http://www.drugs.com/cdi/camphor-liquid.html). Best to call Poison Control and go to nearest emergency department.