Mecholyl in iontophoresis compared to histamine tends to have which characteristic?

• A. It produces more systemic effects than histamine
• B. It is absorbed more slowly and in deeper layers
• C. It is never absorbed into tissues
• D. It is ineffective for any ulcers

Answer: (B)

In iontophoresis, how a drug moves into the skin depends on its size and how the electric field moves it. Mecholyl (methacholine) is a larger, charged molecule, so it doesn't rush into the superficial layers the way a smaller molecule like histamine does. Its larger size means slower electromigration, and the current can push it deeper into the tissues over time. So, compared with histamine, Mecholyl tends to be absorbed more slowly but reaches deeper skin layers. This contrasts with histamine, which is smaller and quickly traverses the superficial tissues to produce rapid local effects. The other statements don’t fit the typical behavior of these agents under iontophoresis: systemic effects aren’t reliably greater with Mecholyl than histamine, complete lack of tissue absorption isn’t accurate, and it isn’t universally ineffective for ulcers.