The duration of a visible biological effect need not match the duration of detectable drug in plasma. This early route-comparison study illustrates that distinction. Primary study
What was measured
Three male volunteers participated in a randomized crossover comparison of intravenous, subcutaneous, and oral Melanotan I. The study measured plasma immunoreactivity and skin reflectance. It reported subcutaneous exposure comparable to intravenous delivery under the tested conditions, no detectable plasma drug after oral dosing, and pigmentation persisting after the administration period. Primary report
Our appraisal: exposure and response have different clocks
A short plasma half-life does not imply that every downstream response ends when plasma levels fall. A biological system can retain the consequences of earlier signaling. Conversely, a lasting visible effect does not prove that intact peptide remains in circulation for the same duration.
“Not detected” is an assay-specific statement. Its interpretation depends on sensitivity, sampling times, and what molecular forms the assay recognizes. It should not be expanded into proof that absolutely no material entered the body.
Bioavailability estimates also belong to the tested formulation and conditions. A result from a very small controlled study does not validate every product or establish interchangeable exposure across routes in general use. The three independent participants remain three, regardless of the number of collected samples.
Crossover designs require attention to washout, especially when a pharmacodynamic effect persists beyond the plasma-exposure period. Baseline skin measurements and sequence effects are therefore relevant to interpreting the pigmentation comparison.
This report contributes to route-specific pharmacology. It does not establish broad safety, justify an administration schedule, or show that pigmentation prevents long-term light-related harm. Full review should examine individual concentration curves, assay validation, sequence allocation, and adverse-event ascertainment before quantitative generalization.
Frequently asked questions
How many volunteers were studied?
Three.
Were several administration routes compared?
Yes.
Was oral plasma drug detected under these conditions?
No.
Does nondetection prove absolute zero absorption?
No.
Did pigmentation last beyond administration?
Yes.
Does that imply equally persistent intact plasma peptide?
No.
Why does washout matter here?
Persistent biological effects can influence later crossover periods.