Tmax – the time taken for a drug to reach the highest (maximum) concentration.
Glossary
Selected words and phrases
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 cis and trans women and other transgender and non-binary people.
NRTI – Nucleoside Reverse Transcriptase Inhibitor, a type of HIV drug – also called ‘nuke’ or ‘nucleoside analogue’.
3TC (lamivudine). abacavir, AZT, FTC (emtricitabine), d4T (stavudine), ddI (didanosine) all belong to this class.
Tenofovir DF and tenofovir alafenamide (TAF) are a nucleotide analogues which is similar enough to be counted as part of this class.
null hypothesis – in a study this sometimes just refers to the hypothesis, but more specifically it refers the idea that any difference between 2 study groups has only occurred by chance.
compartment – place in the body that has barriers limiting both HIV and HIV drugs from moving freely. Key sites include the brian, the genital tract and some organs. Also called sanctuary sites.