Stability of hydrocortisone salts during iontophoresis

Abstract The effect of pH on the stability of hydrocortisone sodium succinate (HCSS) and hydrocortisone sodium phosphate (HCSP) during iontophoresis has been evaluated. It was found that the stability of the drugs are dependent on the pH shifts induced in the matrices due to the applied current. These pH shifts are the result of the migration of ions toward the appropriate electrode and due to the oxidation and reduction occurring at the negative and positive electrode, respectively. It was found that short term sampling of the entire receptor cell provided a closer laboratory estimate of the in vivo situation. The technique prevented the drug from being exposed to conditions that cause its degradation. The microenvironment of the matrix may be buffered to prevent pH shifts and protect the model compound from degradation. This was done in the case of HCSP to protect it from hydrolysis/ degradation in the receptor cell and ensure an accurate analysis of its transport. It must be noted, however, that buffering of a matrix causes the introduction of ions from the buffer salts. These ions will compete with the drug for the applied current and reduce the drug delivery efficiency of the system, especially when the donor matrix is buffered.