Peptides are a class of compounds used to treat diseases ranging from cancer and HIV to diabetes. They are naturally occurring molecules composed of 20 amino acids used by our bodies as the building blocks for proteins and signaling molecules.
As drugs, peptides offer unparalleled specificity and toxicity profiles but have challenges, among them poor pharmacokinetics and no oral bioavailability meaning they don’t last long in the body and must be taken by injection.
Peptides are rapidly cleaved by proteases and/or filtered by the kidneys resulting in half-lives on the order of minutes. To compensate for the short half-lives of peptides and to keep the drug concentration within the therapeutic window for the maximum amount of time, patients are given higher than physiological doses that result in toxic side effects such as nausea, vomiting, and hypersensitivity and have to be taken by injection up to twice daily!
In the case study of one FDA approved peptide drug for the treatment of type 2 diabetes, patients are precribed a twice daily injection of 5 micrograms for 4 weeks and increased to 10 micrograms twice daily for the duration of the treatment. The graphs below illustrate the relationship of increased dosage to adverse side effects.