Once ritonavir transformed into Form II, it was nearly impossible to convert it back to Form I due to a much taller energy barrier and a deeper energy valley for Form II.

A tiny bit of Form II ritonavir acted as a nucleation site, lowering the activation energy and causing all Form I to crystallize into Form II, with seed crystals spreading through the air.

There are at least five known forms of ritonavir, not just two.

Abbott stated that the semi-solid formulation of ritonavir began to change into a crystal form, a transformation they believed was a scientific and chemical impossibility.

Ritonavir production at an alternative factory in Italy initially passed dissolution tests.

Technicians found that the clear ritonavir capsules were turning white and cloudy, filled with millions of tiny needle-like crystals.