On-demand dosing – a term for taking medicines only at times linked to a relevant event.
On-demand dosing for PrEP is also called “event-based dosing” (EBD).
For example, on-demand dosing for PrEP (to prevent HIV transmission) involves taking PrEP before sex and then for several days after sex.
For many years, on-demand dosing referred to 2:1:1 dosing. This was an option for cisgender gay and bisexual men using PrEP. This involves starting with a double dose (two pills), taken 24 to 2 hours before sex, and then single daily doses for the two days after sex.
In 2025, UK (BASHH) and European (EACS) PrEP guidelines included 2:7 on-demand dosing for cisgender women and for transgender and non-binary people.
AST (aspartate aminotransferase; also called serum glutamicoxaloacetic transaminase; SGOT) – an enzyme that is made in many places throughout the body (heart, intestines, muscle) , which is monitored (as with ALT) routinely in HIV-positive people on ARVs to detect liver toxicity from HIV drugs (or other medications). Elevated AST that is specifically made in the liver signals liver injury, but does not indicate how serious liver damage is.
Information on liver tests.
mg (milligram) – abbreviation for milligram. 1000 milligrams = 1 gram.
generic drug – drug supplied under its common (chemical) name.
fusion inhibitor – a type of HIV drug (an entry inhibitor). Fusion inhibitors stops HIV ‘fusing’ to a CD4 cell. T-20 (enfuvirtide, Fuzeon) is only currently licensed fusion inhibitor.
Drug targets in the virus life cycle.
