Inhalation/ Pulmonary Administration:

• Drugs are given through breathing via nasal passage. Some drugs are also inhaled through the mouth.
• Once the drug reaches the lungs, drug is absorbed from alveoli into the bloodstream and distributed rapidly throughout the body.
• Lipid soluble volatile liquid substances and gases are rapidly absorbed from alveoli and produces mainly systemic effects whereas non-volatile, polar or ionized substances remains largely unabsorbed in respiratory tract and produces local effects.

Advantages:

• It provides rapid onset of systemic action for volatile liquids and gases because the alveoli offer highly vascular thin mucous membrane and vast surface for drug absorption.
• Provides controlled administration of drug for moment-to-moment adjustment.
• Avoids drug loss through hepatic and intestinal first pass effects.
• It is suitable for respiratory tract disease where many drug remains unabsorbed and have only local effects.

Disadvantages:

• Requires special techniques or devices.
• Not suitable for irritant vapor and gases because such drugs cause irritation and inflammation of respiratory tract.
• It is difficult to regulate the exact amount of dosage.
• It is not a convenient route for domestic animals.