Fenistil drops and Singulair are medications that can be used in children, but their concomitant administration requires consultation with a doctor. There are no significant interactions between Singulair and other antihistamines, including Fenistil, suggesting that they can be used together.

Fenistil is an antihistamine used to treat allergic symptoms. The dosage for children under 12 years of age is 2 drops/kg body weight/day in 3 doses. The maximum daily doses are:
1 month - 1 year: 30 drops (1.5 mg) 1 - 3 years: 45 drops (2.25 mg) 3 - 12 years: 60 drops (3 mg)

Singulair (montelukast) is usually used in doses appropriate to the age and weight of the child.

If you need more personalized advice, you can use teleconsultations here:

https://www.gdziepolek.pl/telekonsultacja/z-pediatra

Through Gdziepolek, it is possible to book medicines in a selected pharmacy:

https://www.gdziepolek.pl/produkty/29503/fenistil-krople/apteki

https://www.gdziepolek.pl/produkty/71332/singulair-5-tabletki-do-ssania-gryzienia-zucia/apteki