Seretide 250 accuhaler contains two medicines salmeterol and fluticasone propionate salmeterol is a long acting bronchodilator bronchodilators help the airways in the lungs to stay open which makes it easier for air to get in and out the effects last for at least 12 hours fluticasone propionate is a corticosteroid which reduces swelling and irritation in the lungs this has been prescribed for you to help prevent breathing problems such as asthma chronic obstructive pulmonary disease