Drug delivery methods like oral inhalation, nasal sprays, transdermal patches, eye drops, intravitreal injection, and rectal administration provide localized effects with reduced toxicity.

Oral inhalation and nasal sprays swiftly transfer drugs across the respiratory epithelium's mucosal layer. Inhaled glucocorticoids and bronchodilators directly target lung conditions such as asthma, while fluticasone nasal spray mitigates allergic rhinitis.

Transdermal patches transport drugs through the skin into the bloodstream for systemic effect. Controlled-release patches include nicotine patches for smoking cessation, fentanyl for pain relief, and nitroglycerin for angina pectoris.

Eye drops deliver drugs through the conjunctival epithelium, with compounds like dorzolamide reducing intraocular pressure in glaucoma patients. Intravitreal injections introduce drugs like ranibizumab into the vitreous humor of the eye to address age-related macular degeneration.

Rectal administration of drugs is another significant route, with approximately 50% of the absorbed drug bypassing the liver, reducing hepatic first-pass metabolism. However, this administration method presents challenges, including irregular and incomplete absorption and potential irritation of the rectal mucosa. Despite these drawbacks, it can be desirable in certain instances, such as opioid use in hospice care.

These methods demonstrate the diverse routes of administration for therapeutic drugs, each offering its own benefits and challenges.