tropism – the type of coreceptor used by HIV in order to attach to and then infect a cell. If HIV uses the CCR5 coreceptor on the surface of the a CD4 cell it is called R5-tropic. If it uses the CXCR4 co receptor it is called R4-tropic). Early HIV infection is usually R5-tropic but over time, especially in late disease (if CD4 counts drop to less than 50 cells/mm3) the virus shifts to being X4-tropic. Mixed tropic refers to a having some viruses that use R5 and some that use X4.
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 cisgender women and for transgender and non-binary people.
sanctuary site – see compartment site.
DAA (direct acting antiviral) – new hepatitis C drugs that work directly against the hepatitis C virus (HCV).
The following links are to UK prescribing information for DAA combinations plus ribavirin.
Elbasvir/grazoprevir
https://bnf.nice.org.uk/drugs/elbasvir-with-grazoprevir/
Sofosbuvir/ledipasvir
https://bnf.nice.org.uk/drugs/ledipasvir-with-sofosbuvir/
Glecaprevir/pibrentasvir
https://bnf.nice.org.uk/drugs/glecaprevir-with-pibrentasvir/
Sofosbuvir/velpatasvir
https://bnf.nice.org.uk/drugs/sofosbuvir-with-velpatasvir/
Sofosbuvir/velpatasvir/voxilaprevir
https://bnf.nice.org.uk/drugs/sofosbuvir-with-velpatasvir-and-voxilaprevir/
Ribavirin (RBV)
https://bnf.nice.org.uk/drugs/ribavirin/
Additional information is available from the MHRA website.
https://products.mhra.gov.uk/
hepatotoxicity – the medical term for liver-related side effects