Final answer:
For a routine colonoscopy, a patient with valvular heart disease should be prescribed antibiotics as a preventive measure against bacterial endocarditis.
Step-by-step explanation:
A patient with a history of valvular heart disease undergoing a routine colonoscopy would require a prescription for antibiotics before the procedure. This is a preventative practice known as antibiotic prophylaxis, which is used to prevent an infection of the heart's valves, known as bacterial endocarditis. Bacterial endocarditis can occur when bacteria enter the bloodstream, which can happen during medical procedures like a colonoscopy, especially in patients with existing heart conditions. Administering antibiotics prior to the procedure mitigates this risk. Commonly, dental procedures are associated with the need for antibiotic prophylaxis, but other non-sterile procedures may warrant this protective measure as well.