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What is Symdeko (Tezacaftor/Ivacaftor)?

Cystic fibrosis (CF) is a genetically inherited disease that results in persistent lung infections and gastrointestinal issues that gradually damage many organs. It affects the lungs the most, but also the digestive system, including the pancreas, liver, intestines, and kidneys. CF may also impact the ears, nose and sinuses, sex organs, and the bones and joints.

What is the CFTR gene?

People with CF inherit two copies of a defective or mutated CF gene, meaning each parent was a carrier for CF. Called the cystic fibrosis transmembrane conductance regulator (CFTR) gene, this mutation affects production of the CFTR protein. A properly made CFTR protein helps cells move chloride, an element in salt, to the cell surface. In CF, the body creates a “broken” CFTR protein that can’t move chloride properly. Without chloride, water isn’t attracted to the cell surface, resulting in a thick, sticky mucus building up in the lungs and other organs.

A class of drugs called CFTR modulators target specific defects in the CFTR protein so that it can work properly. One such drug is tezacaftor/ivacaftor, which goes by the brand name Symdeko.

How does Symdeko work?

The CFTR modulator tezacaftor/ivacaftor is a combination of two drugs that work in two ways to help the CFTR protein move chloride across a cell surface.

Tezacaftor is what is known as a corrector. This means that tezacaftor helps the CFTR protein form the correct shape so that it can move to cell surface. Once there, about a third of the CFTR protein gets to the cell surface, which is still not enough to move chloride through the surface. That is why another CFTR modulator, ivacaftor is added. Ivacaftor is called a potentiator because it works differently than a corrector. Ivacaftor holds the “gate” on the cell surface open long enough for the chloride to pass through. Combined, these two modulators reduce the symptoms of CF by rehydrating the thick, sticky mucus which makes it thinner.

Tezacaftor/ivacaftor works only for a long as it is in the system, or about 12 hours. That is why the medication is prescribed to be taken every 12 hours. Tezacaftor/ivacaftor does not completely restore proper chloride flow in the cells or reverse lung damage, but it does reduce the symptoms of CF.1,3

What types of cystic fibrosis can Symdeko treat?

Tezacaftor/ivacaftor (Symdeko) can be prescribed to people with CF who are 12 and older. They must have two copies of the F508del mutation for the medication to work. It is also approved for people who have a single copy of one of 26 specified mutations. These mutations are listed below:1

Residual Function Mutations




Splice Mutations





Why genetic testing is important in cystic fibrosis

CFTR modulators are designed to correct the specific type of malfunction that certain CF mutations cause. If you do not have one of these mutations, tezacaftor/ivacaftor will not work to correct why your CFTR protein fails to carry chloride through cells. This is why it is important to know which genetic mutation for CF you have. If you do not know your mutation, the CF Foundation offers free genetic testing for people with cystic fibrosis.

How is Symdeko taken?

Tezacaftor/ivacaftor is prescribed to people with CF who are aged 12 or older. Usually, one tablet of tezacaftor/ivacaftor is taken in the morning followed by one tablet of ivacaftor about 12 hours later in the evening. Both doses must be taken with foods that contain fat, such as peanut butter, avocado, whole milk, eggs, nuts, or butter.1,2

What are the risks or common side effects with Symdeko?

The most common side effects of tezacaftor/ivacaftor (Symdeko) are headache, nausea, sinus congestion, and dizziness. This drug can be hard on the liver so people taking it should be tested regularly for elevated transaminase (AST and ALT).2

Written by: Jessica Johns Pool | Last reviewed: September 2019
  1. Cystic Fibrosis Foundation.CFTR Modulator Therapies. Available at: Accessed 5/29/2019.
  2. U.S. National Library of Medicine Daily Med. Symdeko – tezacaftor and ivacaftor. Available at: Accessed 5/29/2019.
  3. Cystic Fibrosis Foundation. CFTR Modulator Types. Available at: Accessed 5/29/2019.