Treatment training manual

9. Resistance course: glossary

These words are used in the resistance guide.

Links are to the i-Base website glossary and sometimes include further information.

active – an active drug is a drug that still works to reduce viral load. The virus is still sensitive to that drug.

amino acids – amino acids are the building blocks of proteins. DNA codes for amino acids. Three nucleotides (segments of the genetic code) make one amino acid. Amino acids are critical to life, and have many functions in the way your body works.

baseline test – a blood test taken before treatment is started to see if there is any resistance.

CD4 count – a blood test that indicates the strength of the immune system. The CD4 test is one of the most important indicators for deciding when to start HIV treatment.

clinical cut-off (CCO) – a test result that is associated with an impact on clinical care. With resistance tests a lower CCO is the level below which a drug is still sensitive or active. This is often set at a 20% loss of activity (compared to wild-type HIV). An upper CCO is the level above which the drug is not considered active (ie resistant). This is often set at an 80% loss of activity (compared to wild-type HIV).

codon – the word for the junction on genetic material (DNA or RNA) occupied by three nucleotides (or bases) to form an amino acid.

combination therapy – three or more HIV drugs taken together to treat HIV.

compensatory mutation – this refer to an additional mutation, usually in the context of the fitness of a virus. For example, the mutations that stop a drug from working, often stop the virus from reproducing as well. Additional mutations that return the virus to it’s former fitness are called compensatory mutations. They compensate for the reduced viral fitness.

cross-resistance – when resistance to one drug causes resistance to other similar drugs.

DNA – an abbreviation for the scientific word for genes and genetic material. It is the abbreviation for deoxyribonucleic acid.

drug resistant mutation – a mutation or change that occurs in the HIV genome that reduces a drugs ability to work.

escape mutation – a mutation or change in the genetic structure of HIV that makes it easier to evade the persons immune system (rather than a mutation that stops an HIV drug from working).

genome – the complete genetic information (RNA or DNA) of an organism.

genotype – the genetic makeup of a cell, an organism, or an individual.

genotype test – a test that looks at how the genetic structure of a sample of HIV and whether the virus has changed with drug resistant mutations.

integrase inhibitor – a type of HIV drug that stops HIV genetic material from ‘integrating’ into the DNA in a cell. This is a relatively new family of HIV drugs. Raltegravir, elvitegravir and dolutegravir are all integrase inhibitors.

high level resistance – when an HIV drug no longer works against the virus.

intermediate level resistance – when a drug still has some impact on HIV, but when this is reduced (compared to wild-type HIV) because there is some drug resistance.

low level resistance – when there is some resistance but it does not have any significant impact on how well a drug works. The HIV drug will still work enough to suppress this virus and is still considered active.

major mutation – a drug resistance mutation that has a big impact on whether a drug continues to work. This used to be called a primary mutation.

minor mutation – a drug resistance mutation that has a small impact on whether a drug continues to work. This used to be called a secondary mutation.

monotherapy – using only one drug.

mutation – a change in the genetic structure of an organism (including a virus like HIV).

nucleotide – the building blocks of the genetic code (DNA/RNA). Also called a base.

NNRTI (also called “non-nuke”) – Nnon-nucleoside reverse transcriptase inhibitor, a type of HIV drug.

NRTI (also called “nuke”) –  nucleocide (or nucleotide) reverse transcriptase inhibitor, a type of HIV drug.

partially active – the HIV drug in question will work against this virus but this is reduced compared to wild-type HIV. This is the same as partial resistance, intermediate resistance or partial sensitivity etc.

PEP (Post-Exposure Prophylaxis) – a short course of HIV treatment (usually one month) taken after a potential exposure to reduce the chance of infection.

phenotype (or phenotypic) — relating to how an organism behaves, based on how its genotype relates to the environment. Phenotypic resistance tests look at whether HIV continues to grow in a test tube after increasing concentrations of a drug are added.

phenotype test – a type of drug resistance that tests whether a drug is sensitive or resistance to a sample of HIV.

protease inhibitor – a type of HIV drug. HIV protease inhibitors include atazanavir, darunavir, fosamprenavir, indinavir, nelfinavir, lopinavir/r (Kaletra), ritonavir, saquinavir and tipranavir.

reinfection – catching HIV a second time. When an HIV-positive becomes infected with second strain or type of HIV. Sometimes called superinfection.

replicate – to duplicate, copy or reproduce. It is more scientifically accurate to refer to a virus replicating that than reproducing.

resistance – when the genetic structure of a virus or organism changes so that treatment no longer works.

reverse transcriptase – an enzyme unique to HIV. It is used to convert single-stranded RNA into double-stranded DNA. This is needed before HIV’s genetic material can be integrated in the human DNA.

revertant mutation – this term is used in two ways.

Firstly, when referring to a genetic change that shows the virus is returning to a wild-type genotype.

Secondly, it can also refer to the fitness of a virus. A revertant mutation can also refer to an additional mutation that allows the virus to return to a wild-type phenotype. The second example is also called a compensatory mutation as is compensates for the reduced fitness caused by the first mutations.

RNA – an abbreviation for the scientific word for genetic material found in some types of viruses (ribonucleic acid). It is very similar to DNA but is single-stranded rather than double-stranded.

selective pressure – this is when a factor in the environment causes one type of organism to develop and grow in preference to another. With HIV drug resistance, the presence of a drug exerts selective pressure for resistance to develop. It is based on evolution and the concept of ‘survival of the fittest’.

sensitive – when referring to the activity of a drug, sensitive means that a drug still works. As resistance develops a drug becomes less sensitive. A complete loss of sensitivity implies that a drug is no longer working.

viral load – the amount of virus (for example in blood, genital fluids of tissue sample).

wild-type – HIV that has no drug-resistant mutations.

Last updated: 1 January 2023.