Which agent is sometimes included in rescue medications for acute asthma situations?

The option that includes systemic steroids as a rescue medication for acute asthma situations is correctly identified. Systemic corticosteroids play a vital role in managing severe asthma exacerbations because of their potent anti-inflammatory properties. During an acute asthma attack, inflammation within the airways can severely restrict airflow, and systemic steroids help reduce this inflammation, allowing for improved airflow and alleviating symptoms.

It's important to note that while systemic steroids are effective in relieving acute exacerbations, they are typically not the first-line treatment for mild to moderate episodes. Their use is generally reserved for cases where bronchodilators alone are insufficient or when a more severe response is warranted, such as in emergency settings.

Other options provided do have their uses in asthma management, but they don’t serve as frontline therapies in acute situations in the same way. Oral methylxanthines generally are not preferred due to their side effects and slower onset of action. Inhaled long-acting beta-2 agonists, while useful for maintenance therapy, are not intended for immediate relief of acute symptoms. Inhaled short-acting muscarinic antagonists, though helpful in certain contexts, are not a standard part of rescue inhalers.