Instructor Notes — Chapter 4

Teaching notes

What this chapter is actually for

Two deliverables:

One conceptual: that peptide pharmacodynamics is usually already solved by evolution, and what drug development actually engineers is survival. Semaglutide is not a better GLP-1 agonist than GLP-1. It just lasts.

One practical: the five-question delivery filter. This is the most immediately usable tool in Part I — students can apply it to a product page in ninety seconds and reach a defensible conclusion without any evidence at all. It is also the tool they are most likely to still be using in five years.

Common misconceptions

"Peptides can't be absorbed orally, full stop." Over-learned from §4.1. Oral semaglutide exists. Locally acting oral peptides like linaclotide exist and are designed not to be absorbed. The correct statement is that oral peptide delivery is very hard, requires specific engineering, and produces low and variable yields — not that it is impossible. Students who over-learn this will make the exercise 4.28 error.

"Higher bioavailability is always better." No — consistency matters more. This surprises students and it is the single most useful correction in §4.4. Use the twentyfold-variability example.

"Long half-life = better drug." Usually good for adherence, and it removes the ability to stop. Have students articulate what "no undo button" means for a compound taken without supervision, then hold it for Part III.

"The modifications make the drug work better." They make it last. Receptor activity is essentially unchanged. Students consistently assume improvement in potency; the actual answer — evolution already optimized the pharmacodynamics — is more interesting and reframes the whole field.

"Expensive because greedy." And "expensive because hard." Both are partial. §4.8 separates genuine production cost, recovered development cost, and market structure, and the honest answer uses all three. Resist letting the discussion collapse to either pole; Chapter 12 will do this properly and students who arrive with a simple story will not learn from it.

The hardest point to teach

That closing one elimination route is not enough.

Students grasp "the enzyme destroys it" and "the kidney filters it out" separately, then assume fixing either solves the problem. The exenatide-to-semaglutide progression is the fix, and it is worth drawing on the board as a sequence:

native GLP-1     both exits open              ~1–2 minutes
exenatide        proteolysis closed            ~2–3 hours     (~100× better, still not enough)
semaglutide      both closed                   ~1 week        (~5,000× better)

Ask why exenatide's hundred-fold improvement was not sufficient. The answer — the other exit was still wide open — makes the independence of the two routes concrete in a way the diagram alone does not.

Demonstrations that work

Read three labels side by side. Project Ozempic, Rybelsus, and Byetta from DailyMed. Have students find Dosage and Administration in each. The Rybelsus fasting protocol next to Ozempic's "once weekly, with or without food" produces genuine surprise, and it is a regulator's own document rather than a textbook's claim. This is the highest-value fifteen minutes in the chapter.

The filter, live. Put a real consumer peptide product page on screen — an oral or sublingual one — and run the five questions as a class. Students will notice that questions 1 and 4 are usually answerable from the page and questions 2, 3, and 5 are usually not. That asymmetry is the finding.

The gauntlet, physically. Five students stand in a line, each holding a sign: ACID+PEPSIN, PANCREATIC PROTEASES, BRUSH BORDER, THE WALL, THE LIVER. A sixth walks the line as "the peptide." Each barrier turns them back. Then ask which barrier a protective coating solves — and let them work out that THE WALL is a physical problem no chemistry addresses. Cheap and memorable.

Timing

For a 75-minute session:

If time runs short, cut §4.8 and assign it. Do not cut §4.5 or the label reading.

Assessment notes

Exercises 4.14, 4.17, 4.19, and 4.28 are the discriminating items.

4.28 is the best single question in the chapter — it asks students to attack the tool they were just given, and the correct answer (the filter would have rejected oral semaglutide; it is a burden-shifting device rather than a verdict) requires understanding both what the tool does and what it does not. A student who defends the filter unconditionally has not understood it.

4.31 (score every dossier peptide on the filter, then compare to Chapter 1 confidence scores) is where students often discover their first real calibration error. Grade on honesty of the comparison, not on the scores.