How does HIV treatment work?
HIV is a type of virus known as a retrovirus. Retroviruses use RNA as their genetic code as opposed to DNA which is found in normal viruses and, of course, human cells. The drugs used to treat HIV are therefore called anti-retrovirals. They are also known simply as anti-HIV drugs.

Once HIV gets inside the white blood cells in your immune system that it targets, known as CD4 cells, it will begin to make copies of itself (it will begin to replicate). This replication process involves a series of different stages, and HIV needs certain enzymes for it to be able to complete three of these stages. Most (but not all) anti-HIV drugs have been created to target these enzymes and stop them from helping HIV to make copies of itself. These anti-HIV drugs are said to inhibit these enzymes.

If you inhibit one of these enzymes then you also stop that stage of the replication process. Without one of the stages of replication, the whole process falls down and HIV cannot then make more copies of itself inside that CD4 cell.

Currently, there are three enzymes that anti-HIV drugs target.

The first enzyme is called Reverse Transcriptase. This enzyme helps HIV convert its RNA (its genetic code) into viral DNA inside a CD4 cell at the start of the replication process. This process is known as 'reverse transcription'.

The second enzyme is called Protease, and this helps the HIV inside a CD4 cell divide up into new HIV copies at the end of the replication process.

The third enzyme is called Integrase, and this enables the viral DNA produced after the 'reverse transcription' process to be incorporated into the CD4 cell's own DNA. This process is known as 'integration'.

The different classes of anti-HIV drugs
Anti-HIV drugs are divided into different classes. These different classes of drugs do different things to stop HIV replicating.

There are six different classes currently available:

Nucleoside Reverse Transcriptase Inhibitors – these were the first group of drugs developed, and are abbreviated to ‘NRTIs’ and commonly known as ‘Nukes’. As the name suggests these inhibit the enzyme Reverse Transcriptase.

Nucleotide Reverse Transcriptase Inhibitors – a much newer class of drugs, and similar to the NRTIs above in that they inhibit Reverse Transcriptase. These are abbreviated to ‘NtRTIs’.

Both of these groups of drugs inhibit reverse transcriptase in a similar way, however they have different chemical structures referred to as either ‘nucleoside’ or ‘nucleotide’.

Non-Nucleoside Reverse Transcriptase Inhibitors – the third class of drugs that inhibit Reverse Transcriptase, but in a different way from the two classes above. These are abbreviated to ‘NNRTIs’ and commonly known as ‘Non-nukes’. As with the two classes above, ‘non-nucleoside’ refers to the chemical structure of the drugs in this class.

Protease Inhibitors – as the name suggests, this class of drugs inhibits the enzyme Protease. These are abbreviated to ‘PIs’.

Entry Inhibitors (includes Fusion Inhibitors and CCR5 Antagonists). Unlike the four classes above, Entry Inhibitors don't actually inhibit an enzyme. Instead they stop HIV from binding (or fusing) with, and then entering, a CD4 cell in the first place. These drugs can be abbreviated to ‘EIs’.

Integrase Inhibitors – this newest class of drugs inhibits the enzyme Integrase. These can be abbreviated to ‘IIs’.

Combination therapy
Treatment for HIV is known as ‘HAART’, which stands for Highly Active Anti-Retroviral Therapy. Usually, at least three drugs from two or more classes of anti-HIV drugs are used together in combination which is why HIV treatment is also sometimes called combination therapy.

The most common combinations of anti-HIV drugs consist of two different drugs from the NRTI / NtRTI classes, then a third drug from either the NNRTI or the Protease Inhibitor class (although Protease Inhibitors are often boosted by a fourth drug, which we talk about in the anti HIV-drugs currently available section below). The two drugs from the NRTI / NtRTI classes are often referred to as your treatment backbone.

These days, most people don’t have to take the drugs more than twice a day, and there are some combinations available that only need to be taken once a day.

Anti-HIV drugs currently available
Below are some tables showing the different anti-HIV drugs currently available. The drugs in each class usually have more than one name. The main names listed in the tables below are the ones most commonly used in the UK. As well as these names, each drug has a brand name given by the drug company that make it. Some drugs, especially those in the NRTI and NtRTI classes, have yet another name. These other names are more commonly used in the US than the names we use in the UK. The dosages given here are the standard dosages prescribed. However, dosages can vary; for instance if you weigh less than 60kg, dosages of certain drugs will probably be lower. To get more information on the different anti-HIV drugs available, click on the "Read More" buttons below. 

NRTIs
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NtRTIs
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Protease Inhibitors (PIs)
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In most cases these days, protease inhibitors are taken with a small dose of another protease inhibitor called ritonavir (brand name Norvir). The ritonavir acts to boost the levels of the main protease inhibitor in the blood, helping to ensure that levels don’t fall too low to allow HIV to become more active again. Protease inhibitors taken with ritonavir in this way are therefore referred to as ‘boosted PIs’. Ritonavir is almost always only used as a booster, and rarely prescribed as the only protease inhibitor in an anti-HIV drug combination.
NNRTIs
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Entry Inhibitors
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Integrase Inhibitors
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Fixed Dose Combinations
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Fixed dose combinations contain two or more different anti-HIV drugs combined into just one pill. They are known as ‘fixed dose’ since doctors cannot alter the dosage of any of the drugs contained in these pills. These pills have been developed to reduce the number of pills that people taking anti-HIV drugs have to take.