A 45-year-old woman with known severe persistent asthma presents to her GP complaining of increased wheeze and shortness of breath over the past 3 days, requiring her salbutamol inhaler every 2-3 hours. Her peak expiratory flow rate (PEFR) is 65% of her personal best. She is currently prescribed a high-dose inhaled corticosteroid (ICS) and a long-acting beta-agonist (LABA) combination inhaler, and montelukast. What is the most appropriate immediate action?