How is a drug administered through inhalation primarily used?

A drug administered through inhalation is primarily used for delivering medication directly to the lungs, making it especially effective for conditions that affect the respiratory system, such as asthma and chronic obstructive pulmonary disease (COPD). Inhalation allows for rapid absorption of the medication, which can quickly open airways, reduce inflammation, and relieve symptoms such as wheezing and shortness of breath. This route of administration is suitable for bronchodilators and corticosteroids, which are commonly used in the management of these respiratory conditions.

Other options do not align with the inhalation route. Treating yeast infections typically involves antifungal medications administered orally or topically rather than through inhalation. Cleansing the bowel is generally achieved through specific solutions or enemas, and oral hydration refers to the intake of liquids, which again doesn't involve the inhalation route. Therefore, the inhalation method is specifically beneficial for respiratory treatments where localized delivery of medication is essential for efficacy.