Which of the following could be an adverse reaction associated with Procainamide?

Procainamide is an antiarrhythmic medication used to treat certain types of irregular heartbeats. One of the known adverse reactions associated with Procainamide is skin reactions, which can include itching or other dermatological symptoms. This is likely due to its potential to cause hypersensitivity reactions in some patients.

While dry mouth, insomnia, and constipation can occur with various medications, they are not specifically prominent or well-documented side effects of Procainamide. Itching can indicate a more direct reaction involving the skin, making it a clearer connection to the use of this drug. Skin reactions, including itching, can occur due to the body’s immune response to the drug or its metabolites.

Therefore, the association of itchy skin with Procainamide is well established in the pharmacological literature, making it the correct answer in this scenario.