The pharmaceutical blockbuster model is wobbling. And no single franchise is safe. While king Keytruda, Merck’s stalwart oncology drug, continues to rule the first half of 2025 with $15.2B in sales (Q1 $7.2B, Q2 $8.0B), its U.S. patent expiry in 2028 the single biggest loss of exclusivity event on the horizon. In the U.S., Medicare…