The most appropriate secondary prophylaxis for a patient who has had acute rheumatic fever with carditis is the intramuscular injection of penicillin G benzathine every 21-28 days until they reach the age of 40. This recommendation is grounded in the understanding that individuals with a history of rheumatic fever, particularly those who have experienced carditis, are at an increased risk of developing rheumatic heart disease and subsequent infections from streptococcal bacteria.
Secondary prophylaxis aims to prevent recurrent episodes of rheumatic fever and mitigate long-term complications. The American Heart Association guidelines indicate that after a first episode of rheumatic fever with carditis, the recommended duration for prophylaxis extends until at least 10 years after the most recent episode or until the patient reaches 40 years of age, whichever is longer. This means that if a patient had their last episode of rheumatic fever at 30 years old, they would continue prophylaxis until they were 40. If they had their last episode at 32 years old, they would need the prophylaxis for 8 more years or until they reach 40.
The other options, such as receiving the injections for a fixed 10-year period or using oral medications, do not align