Paxlovid®: active ingredient and side effects

Paxlovid®: active ingredient and side effects

High incidences, the highly contagious omicron variant and stagnating vaccination rates: the coronavirus still plays a significant role in everyday life. The unvaccinated and people from risk groups are particularly at risk from COVID-19. The corona drug Paxlovid® from Pfizer reduces the risk of hospitalization and death by 89 per cent. The unique feature: It can be taken in tablet form at home to prevent a severe course if an infection is detected. What active ingredient is Paxlovid® based on, for whom is the drug approved, can it be bought, and what are its side effects?

Paxlovid® – which active ingredient is used?

The main active ingredient of the pill against corona is nirmatrelvir (development name PF-07321332), administered together with the antiviral drug ritonavir. Ritonavir is already used in HIV therapy and inhibits the rapid breakdown of nirmatrelvir in the body.

Nirmatrelvir is a protease inhibitor. This means that this ingredient is supposed to prevent the activity of protein-splitting enzymes, which accelerate the metabolic processes of the cells. The active substance should, therefore, block the enzyme that the coronavirus needs to multiply in the body.

A detailed list of all the ingredients of Paxlovid® is included in the package leaflet.


Studies show the high effectiveness of the coronavirus drug.

Overall, the approval study was carried out with around 2,200 people who had been infected with COVID-19 within the last five days and suffered from at least one disease symptom. The participants also met at least one risk factor for a severe course and were given either the drug or a placebo in this early phase of the disease.

An early interim evaluation based on high success rates showed that the drug was effective. Only three of 389 participants (0.8 per cent) who were treated with Paxlovid® within the first three days had to be hospitalized or died from the infection. In the placebo group, on the other hand, there were 27 out of 385 participants (7 per cent).

Based on the positive study results, the researchers calculated the effectiveness of the corona drug at 89 per cent, provided Paxlovid® is taken within the first three days after the onset of symptoms. The first laboratory tests show that the drug should also work against the omicron variant.

Approval: Who can use Paxlovid®?

The conditional approval of Paxlovid® by the EMA was granted in January 2022. Paxlovid® has been available in Germany since February 2022. The drug can currently be used in people over the age of 18 who are not yet artificially ventilated and have an increased risk of suffering a severe course of COVID-19. This applies, for example, to people who are older or who have previous illnesses such as diabetesoverweight or heart or lung disease.

The Robert Koch Institute recommends use primarily in those affected who show no or only mild symptoms and who are not or only partially vaccinated but at the same time have one or more risk factors for a severe course. Use is also recommended for those affected at high risk of vaccination failure. Consideration should be given to use in fully vaccinated subjects with a complex risk profile.


Taking the tablets: what should be considered?

Paxlovid® consists of three tablets:

  • two tablets, each containing 150 milligrams of nirmatrelvir
  • a tablet containing 100 milligrams of ritonavir

All three tablets must be taken together at the same time. It is taken twice daily (morning and evening, 12 hours apart) for five days.

The first dose should be started within five days after confirmation of COVID-19 infection (by a positive PCR or antigen test). It can be taken at home as long as there are no medical reasons for hospitalization.

Paxlovid®: Side effects are minor

According to the manufacturer, Pfizer, the drug is generally well tolerated. The European Medicines Agency (EMA) also confirms this assessment.

The following side effects frequently occurred, i.e. in more than one but less than ten per cent of cases:

In addition, abdominal pain was uncommon, and malaise was rare. No other side effects of Paxlovid® are known to date.

Who should not take Paxlovid®?

Some medications and existing medical conditions should be consulted with your doctor before taking Paxlovid®. Depending on the disease stage, the drug dosage should be adjusted in the case of existing renal insufficiency or, in the case of severe renal dysfunction, not used. The use of Paxlovid® should also be avoided in the case of severe liver diseases . If the HIV infection is not controlled, taking the corona drug may trigger resistance to specific HIV protease inhibitors that are used to treat the HI virus. 

As with other medications, Paxlovid® should not be taken if you are allergic to ingredients.


Paxlovid® during pregnancy and lactation

The use of Paxlovid® during pregnancy is not recommended unless the state of health of the person concerned makes the use of the drug unavoidable. There is no data available on the effects of the drug during pregnancy. However, there are already study results on using the individual active ingredients contained in Paxlovid®.

Data from animal experiments on rats and rabbits are available for the active substance nirmatrelvir. Except for the fetus’s reduced body weight, no ingestion effects could be determined in these studies. The extent to which these results can be extrapolated to humans remains to be seen.

There is data from human studies on the use of ritonavir during pregnancy. These showed no effects on the fetus.

It is not yet known whether nirmatrelvir can pass into breast milk, but individual data point to this for ritonavir. To rule out health risks for the baby, Paxlovid® should not be used while breastfeeding. Alternatively, breastfeeding should be discontinued during use and one week after stopping use.

Drug Interactions

Some medications may interact with Paxlovid®, which can affect the way the medication works or cause serious side effects.

Relevant medications include:

  • Cancer drugs (venetoclax and neratinib)
  • Drugs used to treat heart disease and heart rhythm disorders (including dronedarone and bepridil)
  • Fusidic acid and rifampicin to treat bacterial infections
  • certain allergy medicines (terfenadine, astemizole)
  • St. John’s wort preparations
  • Drugs used to treat sleep and anxiety disorders (such as diazepam flurazepam)

A complete list is included in the package insert. Before taking Paxlovid®, inform the doctor treating you about any previous illnesses or medication you are taking.

Can you buy Paxlovid®?

You can’t just buy Paxlovid®. The drug is available in pharmacies and must be prescribed by a doctor. The doctor treating you will first conduct a patient interview (anamnesis) and then – after weighing up the benefits and risks – prescribe the medication. Proof of infection with COVID-19 is also required for the prescription. A positive antigen rapid test is also sufficient for this.

The medication can be picked up at the pharmacy if the doctor’s prescription is available. Initially, pharmacies were allowed to have a maximum of two packs of Paxlovid® in stock. However, this rule was repealed on June 29, 2022.

Alternatively, since August 19, 2022, general practitioners have had the option of handing out the medicine directly to affected people. With this, the Federal Ministry of Health wants to lower the hurdles for the use of Paxlovid®. Up to five packs of Paxlovid® may be stored in general practitioners’ surgeries.

The costs (the price for a pack of Paxlovid® is around 500 euros) are covered by the Federal Social Security Office.

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