science

Pre-exposure prophylaxis

Pre-exposure prophylaxis is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pre-exposure prophylaxis rather than just read about it. In short: Pre-exposure prophylaxis (PrEP) is the use of medications to prevent the spread of disease in people who have not yet been exposed to a disease-causing agent. Vaccination is the most commonly used form of pre-exposure prophylaxis; other forms of pre-exposure prophylaxis generally involve drug treatment, known as chemoprophylaxis.

Key takeaways

Pre-exposure prophylaxis belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pre-exposure prophylaxis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pre-exposure prophylaxis from memory before moving on to harder problems.

Reference excerpt

Pre-exposure prophylaxis (PrEP) is the use of medications to prevent the spread of disease in people who have not yet been exposed to a disease-causing agent. Vaccination is the most commonly used form of pre-exposure prophylaxis; other forms of pre-exposure prophylaxis generally involve drug treatment, known as chemoprophylaxis. Examples include taking medication to prevent infection by malaria or HIV. In particular, the term PrEP is now synonymous in popular usage with the use of pre-exposure prophylaxis for HIV prevention. In general, the use of pre-exposure prophylaxis requires balancing the risks of the treatment (e.g., side effects from a drug) to healthy individuals with the risk of the disease. It is contrasted with post-exposure prophylaxis (PEP), which is used once the patient has already been exposed to the infectious agent.

Use of pre-exposure medication against specific diseases

Malaria

The use of pre-exposure drug treatment to prevent malaria using antimalarial drugs is well-established, with the use of quinine as a prophylactic treatment dating back at least to the 19th century.

HIV/AIDS

The abbreviation PrEP now often refers to pre-exposure prophylaxis for HIV prevention, the use of antiviral drugs as a strategy for the prevention of HIV/AIDS. PrEP is one of a number of HIV prevention strategies for people who are HIV-negative but who have a higher risk of acquiring HIV, including sexually active adults at increased risk of contracting HIV, people who engage in intravenous drug use (see drug injection), and HIV-negative members of serodiscordant sexually active couples. When used as directed, PrEP has been shown to be highly effective at preventing HIV infection, reducing the risk of acquiring HIV by up to 99%. A large-scale study in the UK has shown that PrEP remains effective at preventing HIV infection, even when used in uncontrolled environments.

COVID-19 Pre-exposure prophylaxis against infection by SARS-CoV-2, the virus that causes COVID-19, has been studied as a possible preventive measure for high-risk groups. In December 2021, the US FDA granted emergency use authorization (EUA) of the antibody drug tixagevimab/cilgavimab (Evusheld) to prevent COVID-19 in immunocompromised people who cannot be fully vaccinated due to a history of a severe reaction to coronavirus vaccines. However, due to the high levels of non-susceptible SARS-CoV-2 variants present in the US, the FDA announced on 6 January 2023 that tixagevimab/cilgavimab was no longer currently authorized for emergency use in the US. In March 2024, pemivibart (Pemgarda), a monoclonal antibody drug, received an emergency use authorization from the US FDA to protect certain moderately to severely immunocompromised individuals against COVID-19.

Rabies Pre-exposure prophylaxis against infection by the rabies virus, the virus that causes rabies, is recommended for high-risk individuals such as veterinarians, travelers to rabies-endemic areas, and individuals from rabies-endemic areas (especially children and people from rural areas where rabies post-exposure prophylaxis might not be readily accessible). The standard dosage for rabies pre-exposure prophylaxis is two 1ml doses of the rabies vaccine (HDCV, PCEC, or PVRV) administered intramuscularly (IM) on Days 0 and 7. The vaccines used for rabies pre-exposure prophylaxis are the same ones used for post-exposure prophylaxis.

Pre-exposure prophylaxis for post-mortems Since conducting autopsies may involve inadvertent cuts, and the incidence of hepatitis-B can be very high in certain populations, it is advisable for all autopsy personnel to get their hepatitis-B antibody status tested. If antibodies are not present in sufficient concentrations, a hepatitis-B vaccine is recommended.

References

Worked examples

Example 1 — a first encounter with Pre-exposure prophylaxis

Start with the simplest possible case. Write down what Pre-exposure prophylaxis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pre-exposure prophylaxis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pre-exposure prophylaxis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pre-exposure prophylaxis

In research: Pre-exposure prophylaxis appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pre-exposure prophylaxis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pre-exposure prophylaxis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical treatments, Pre-exposure prophylaxis, so understanding it makes those chapters shorter.
In everyday life: Look for Pre-exposure prophylaxis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pre-exposure prophylaxis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pre-exposure prophylaxis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pre-exposure prophylaxis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pre-exposure prophylaxis in simple terms?

Why does Pre-exposure prophylaxis matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pre-exposure prophylaxis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pre-exposure prophylaxis.