Which adverse effect should a client taking rifampin and ethambutol for tuberculosis report?

The correct answer highlights a significant concern for patients taking ethambutol, which can cause ocular side effects, including decreased visual acuity. Ethambutol is known to potentially lead to optic neuritis, an inflammation of the optic nerve, which may manifest as vision changes, blurred vision, or decreased visual acuity. Therefore, it is crucial for patients on this medication to be vigilant about their vision and report any changes promptly to their healthcare provider.

While continuous coughing and fever can be related to tuberculosis treatment or the disease itself, they are not direct side effects of the medications listed. Increased appetite is not associated with these drugs, and in fact, both rifampin and ethambutol can result in gastrointestinal upset for some patients, potentially affecting appetite negatively. Thus, decreased visual acuity is the most pertinent side effect that needs immediate attention among those listed.