宝宝咳嗽一周多带他去医院拍的胸片验血,显示是支气管炎,大夫给开的头孢吃了三天没效果,我就给他换吃阿奇霉素干混悬颗粒,早晚各一袋我想问问换吃阿奇最多能给他吃几天?