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HIV is a virus that attacks the immune system, making those infected more susceptible to infection by other diseases. Treatment for HIV often requires the use of multiple medications. Though these medications target many different parts of the virus, most HIV drugs rely on inhibiting enzymes to prevent viral replication. Two of the six types of HIV medications target the same enzyme, reverse transcriptase.

One aspect of HIV that makes it so deadly is its means of infecting its host. HIV is a retrovirus, a type of virus that infects a cell by integrating its own DNA into the host’s genetic material. To do this, an enzyme called reverse transcriptase (RT) is required. Reverse transcriptase helps the virus replicate by taking the genetic material of the virus, in the form of RNA, and converting it to DNA which can then enter the host cell’s genome. Reverse transcriptase is especially effective in the spread of HIV because it tends to make multiple mutations during the conversion to DNA. These mutations make the HIV virus harder to detect, and therefore, more resistant to treatment.

 Illustrated representation of a reverse transcriptase enzyme.

Image Source: Laguna Design

Because of its importance in the replication of HIV, reverse transcriptase is a specific target of some medications. The two primary drug types used for this are nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs).

NRTIs were the first approved drugs to treat HIV. They inhibit the replication of HIV by posing as the “building block” molecules needed to create DNA. Because they are similar in structure, reverse transcriptase cannot distinguish between the two and will use both of them when making new DNA. However, because NRTIs lack a component needed to continue a DNA chain, any chains that include a NRTI cannot finish replicating.

 NRTIs treat HIV by posing as building blocks of DNA and inhibiting replication.

Image Source: Adam Gault

NNRTIs also inhibit the RT enzyme. They do this by binding to the enzyme itself. When bound by NNRTIs, RT can still convert RNA, but will do it more slowly. While NNRTIs are useful when combined with other HIV medications, they are ineffective in treating HIV on their own because the virus can eventually mutate to become resistant.

NRTIs and NNRTIs, while both targeting reverse transcriptase, operate very differently. Though most HIV medications should be taken in conjunction with other types to effectively treat the disease, NNRTIs especially need to be taken with other HIV medications to be effective. If you are in need of HIV treatment, be sure to discuss all possible options with your physician.

Featured Image Source: 334 [meds] by Evan Blaser

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