Final answer:
The true statement about medications acting on gastrointestinal system tissues is that suppositories may cause rectal irritation as they are administered rectally which can lead to irritation.
Step-by-step explanation:
The correct answer to the question Which of the following is true concerning medications acting on gastrointestinal system tissues? is option a, Suppositories may cause rectal irritation. Suppositories are a form of medication administered through the rectum which can lead to irritation due to their route of administration. Xanthine derivatives such as theophylline are indeed used to treat asthma and other respiratory issues due to their ability to relax bronchial muscle, but they are not always the drug of choice because of the narrow therapeutic range and associated risks. Chlorpheniramine, while an antihistamine, is not typically the antihistamine of choice in the elderly due to potential sedation and other side effects. Lastly, mucokinetic agents are not the same as mucolytics; mucokinetics enhance the expulsion of mucus whereas mucolytics break down the mucus making it less viscous. In summary, suppositories could irritate rectal tissues, xanthines have a narrow therapeutic range, chlorpheniramine is not preferred in the elderly, and mucokinetic agents differ from mucolytics.