A medication that cures a deadly chromo-viral infection but was reserved on the Dinaali hospital ship for privileged patients, who received it merely to slow arterial ageing, until the Doctor intervened.
Cytoglobin is the drug at the centre of the Voyager episode Critical Care. The Doctor's programme is stolen and sold to Hospital Ship 4-2, a medical facility serving a Dinaali population, where a computer called the Allocator assigns every patient a treatment coefficient according to their value to society.
On the comfortable Level Blue, patients with high coefficients are given cytoglobin injections as a preventive against arterial ageing. On crowded Level Red, young workers such as Tebbis are dying of a chromo-viral infection that the same drug would cure, but are allowed none of it.
The Doctor begins diverting doses to Level Red. When the administrator Chellick finds out and Tebbis dies, the Doctor takes a drastic step: he infects Chellick with the virus and has him registered as a Level Red patient, so that the administrator must release the medicine in order to save himself.