Ask a doctor or pharmacist before taking this medicine if you have liver or kidney disease. Before taking this medicine. Ask a doctor or pharmacist if loratadine is safe to use if you have ever had: kidney disease; or. liver disease. The disintegrating tablet may contain phenylalanine and could be harmful if you have phenylketonuria (PKU). Ask a doctor before using this medicine if you are. Ask your health care provider about the safety of taking other vitamins, herbal remedies, and supplements. Most herbal preparations and supplements have not been proven to be safe during pregnancy. Skeeter syndrome is an allergic reaction to a mosquito bite. It may involve swelling and a fever. Treatment may involve taking antihistamines or using topical steroids. Learn more about skeeter. People should avoid taking Zyrtec with alcohol or other medicines that could cause drowsiness. Timescales. Zyrtec and Claritin are effective for about 24 hours. A person should only take one dose.