Drug Delivery: Miscellaneous Routes

Oral inhalation and nasal sprays rapidly carry drugs across the respiratory epithelium's mucosal layer. Inhaled glucocorticoids and bronchodilators directly address lung conditions like asthma, while corticosteroid nasal sprays alleviate allergic rhinitis. These routes provide localized effects with minimal systemic toxicity.

Transdermal patches deliver drugs through the skin into the bloodstream, offering controlled-release formulations. Commonly used patches include nicotine for smoking cessation, opioids for pain relief, and nitroglycerin for angina pectoris. This route provides sustained therapeutic levels while minimizing toxicity and avoiding hepatic first-pass metabolism.

Eye drops deliver drugs through the conjunctival epithelium for localized ocular effects, such as dorzolamide reducing intraocular pressure in glaucoma. Intravitreal injections bypass this barrier, delivering drugs like ranibizumab directly into the vitreous humor to treat age-related macular degeneration, providing more direct access to posterior eye structures.

Intrathecal delivery involves injecting a drug into the subarachnoid space to reach the brain and spinal cord. This route bypasses the blood-brain barrier, allowing direct access to the central nervous system. Baclofen injection, for example, effectively treats severe muscle spasms by targeting spinal cord pathways.

Rectal administration allows approximately 50% of absorbed drug to bypass the liver, reducing hepatic first-pass metabolism. This route is desirable in specific instances, such as opioid use in hospice care. However, it presents challenges including irregular absorption, incomplete absorption, and potential irritation of the rectal mucosa.

The route of administration and drug formulation determine whether effects are localized or systemic. Routes like oral inhalation, nasal sprays, eye drops, and intravitreal injections target specific tissues locally with minimal toxicity. Transdermal patches and rectal administration can produce systemic effects by delivering drugs into the bloodstream or bypassing hepatic first-pass metabolism.

Miscellaneous routes offer targeted delivery to specific tissues, reducing systemic exposure and toxicity compared to oral administration. Unlike parenteral routes requiring injections, many miscellaneous routes are non-invasive. Each route—inhalation, nasal, transdermal, ocular, and intrathecal—provides unique advantages for treating localized or systemic conditions based on drug properties and therapeutic goals.