Routes of Administration

Peptide therapeutics are increasingly vital in modern medicine, particularly for metabolic diseases. While subcutaneous injection remains the dominant and most practical delivery method for systemic peptide drugs, advancements in formulation are expanding the possibilities for oral delivery and other non-invasive routes, though these are still the exception.

Subcutaneous Injection: The Dominant Route

Subcutaneous injection is the most common and reliable route for systemic peptide drug administration. This method offers practical advantages and generally provides consistent drug exposure. Examples include tirzepatide (Mounjaro, Zepbound) for diabetes and weight management, which is administered once weekly via subcutaneous injection. Despite its prevalence, absorption can still vary due to factors like local blood flow, lymphatic drainage, and tissue characteristics. Many established peptide drugs, such as octreotide for acromegaly, desmopressin for diabetes insipidus, and teriparatide for osteoporosis, are also administered subcutaneously.

Oral Delivery: A Growing Exception

Historically, oral delivery of peptides has been challenging due to their susceptibility to degradation in the gastrointestinal tract and poor absorption. However, significant progress has been made, making it a notable exception rather than the rule. The flagship example is oral semaglutide (Rybelsus), which is FDA-approved for glycemic control in type 2 diabetes. Its success is attributed to specialized formulations incorporating absorption enhancers like SNAC. Despite this innovation, the absolute bioavailability of oral peptides typically remains low, necessitating higher doses compared to injectable forms. Beyond systemic effects, some peptides, such as linaclotide, are designed for local action within the gastrointestinal tract, bypassing the need for systemic absorption.

Other Routes: Limited Information in Provided Sources

While the prompt mentions transdermal, microneedles, and iontophoresis as routes of administration, the provided source material does not contain specific information or examples regarding these methods for peptide delivery. The focus of the given texts is predominantly on subcutaneous and oral administration, highlighting their current clinical relevance and challenges.

Current Status

Subcutaneous injection remains the cornerstone for systemic peptide drug delivery due to its practicality and reliable exposure. Oral delivery, exemplified by semaglutide, represents a significant breakthrough, though it still requires specialized formulations to overcome inherent challenges. The development pipeline continues to prioritize these routes, with a strong focus on metabolic diseases.