While Benitowa Trio contains a calcium channel blocker, benidipine, which can cause fluid retention and swelling, this side effect typically affects both legs. Swelling in only one leg is unusual for this medication and could indicate a localized issue, such as a blood clot or a vein problem. I gently recommend having his doctor evaluate his leg promptly to rule out these conditions and ensure his safety. Please rest assured, identifying the cause is the best first step to helping him feel comfortable.