Why treating Covid-19 with drugs is harder than you think – BBC News

Unlike broad-spectrum antibiotics, which can be used to treat a wide range of bacterial infections, drugs that work against one type of virus rarely work at treatingother viruses. For example, remdesivir, originally developed for treating hepatitis C, was at one point suggested as a treatment for Covid-19, but clinical trials have shown that it hasonly a limited effectagainst this coronavirus.

The reason there are few effective broad-spectrum antivirals is that viruses are much more diverse than bacteria, including in how they store their genetic information (some in the form of DNA and some as RNA). Unlike bacteria, viruses have fewer of their own protein building blocks that can be targeted with drugs.

For a drug to work, it has to reach its target. This is particularly difficult with viruses because they replicate inside human cells by hijacking our cellular machinery. The drug needs to get inside these infected cells and act on processes that are essential for the normal functioning of the human body. Unsurprisingly, this often results incollateral damageto human cells, experienced as side-effects.

Targeting viruses outside cells to stop them from gaining a foothold before they can replicate is possible, but is also difficult because of the nature of thevirus shell. The shell is extraordinarily robust, resisting the negative effects of the environment on the way to its host. Only when the virus reaches its target does its shell decompose or eject its contents, which contain its genetic information.

This process may be a weak spot in the virus lifecycle, but the conditions that control the release are very specific. While drugs targeting the virus shell sounds appealing, some may still betoxic to humans.

Despite these difficulties, drugs that treat viruses such as influenza and HIVhave been developed. Some of these drugs target the processes of viral replication and the viral shell assembly. Promising drug targets of coronaviruses have beenidentified as well. But developing new drugs takes a long time, and viruses mutate quickly. So even when a drug is developed, the ever-evolving virus might soon developresistance towards it.

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Why treating Covid-19 with drugs is harder than you think - BBC News