Elevated CK (Creatinkinase) in a baby in case of breast-feeding of mother taking Symkevi

Question

My daughter is 7 months old, I breastfeed her and I do not want to stop it now. When she was 5 months old, I started again on modulators (Symkevi/Kalydeco =Tezacaftor/Ivacaftor) because I had a Pseudomonas then and I had been very ill with loss of lung function, etc. My daughter does not have any symptoms, but when she had a control of blood values, the CK-value was increased (544). At the first control of blood values in July the CK-value had been 400 and the GOT (ASAT) value was also increased. It is now at 79, therefore borderline.
My CF-Center has no information that the CK-value could be elevated due to modulators, the pediatrician has no experience in CF and is of the opinion, this could be due to the the muscle strain as she is learning to sit.
Do you have any experience with modulators and increased CK-values?

Answer

Dear questioner,
in general it is known that patients who take modulators (Kaftrio= Tezacaftor, Elexacaftor and Ivacaftor) can have a markedly increased CK-value, mostly triggered by intensive muscle strain (muscle- and cardio-Training), that leads to an alteration of the muscles so they release CK. In such cases, patients have to stop training, then the blood values are controlled, in case the CK does not decrease and the value is still very high, the modulator has to be stopped until the CK-values habe normalized - of course this is dependent on the concrete value.
In case of a baby, there is for sure no trigger for a markedly increased muscle activity, therefore the drug itself could be the reason or there can be a totally different reason.
There is nearly no data on the exposition of babies with modulators via the breastmilk for Symkevi, however, there is data on Kaftrio. As Kaftrio contains the two drugs Tezacaftor and Ivacaftor which are also in Symkevi, plus Elexacaftor, one could try to take the data we have with Kaftrio and speculate it could be similar with Symkevi. The concentration of Kaftrio in the blood of the babies (mothers breastfeeding and taking Kaftrio) has been investigated; the range of the measured concentrations was broad, therefore in the individual case it cannot be predicted how high the concentration in the blood of the baby will be. Therefore it is written in the drug information leaflet that due to lack of data a risk for the baby cannot be excluded and in case of breastfeeding either the mother should interrupt her intake of Symkevi or - if that is not possible due to health condition - the baby should not be breastfed. Therefore exposure of the baby to Symkevi is not recommended.
In your particular case your CF-center can help to decide together with you, which way is the best for you, depending on your health situation. It has to be found out, why the CK and ASAT-value are increased - for this reason Symkevi as a possible cause has to be ruled out, and after 3-4 weeks without Symkevi the blood values should be controlled again and if the values return to normal. If that is not the case, other reasons will have to be taken into account.
Best regards,
Daniela d'Alquen

20.01.2026