Which substance used with iontophoresis has a positive polarity?

Lidocaine is associated with a positive polarity when used in iontophoresis. Iontophoresis involves using electrical currents to deliver ionized medications transdermally. The charge of the medication is critical because it needs to be matched with the polarity of the electrode to facilitate the drug's movement through the skin.

Lidocaine, commonly used for its analgesic properties, carries a positive charge in its ionized form. When applied with a positive electrode (anode), it enhances the delivery of the drug into the tissue, helping to achieve its therapeutic effects such as pain relief.

Other substances mentioned, like salicylates, dexamethasone, and calcium chloride, involve different polarities or therapeutic effects. Salicylates are typically negatively charged and are more commonly used with a negative electrode for anti-inflammatory effects. Dexamethasone is a corticosteroid that also carries a negative charge and is applied using a negative electrode. Calcium chloride can be positively charged but is less commonly compared to lidocaine when considering its application in iontophoresis specifically. Therefore, the characteristic of lidocaine’s positive polarity in iontophoresis makes it the correct choice in this context.