Compositions and methods for enhanced drug delivery

An iontophoretic drug delivery system for administering a pharmaceutical agent to a patient comprising:

• (a) a pharmaceutical agent-chemical modifier complex comprising:
• a pharmaceutical agent, suitable for transdermal transport at therapeutically effective doses of less than 50 milligrams per day, having a derivatizable chemical functionality;
• and
• a charged, naturally-occurring chemical modifier, conjugated to the agent's derivatizable chemical functionality by a covalent, physiologically cleavable bond, wherein said chemical modifier is selected from the group consisting of taurine, betaine, L carnitine, choline, norcholine, lysine, N-methylated amino acids, trigonelline, stachydrine, betonicine, cytochrome c, squalamine, chonemorphine, and conessine;
• where said pharmaceutical agent-chemical modifier complex has a charge-to-mass ratio of at least one charge per 1000 daltons, and
• wherein upon iontophoretic delivery of said composition and cleavage of said covalent bond, said chemical modifier is present at a non-toxic level and said pharmaceutical agent is delivered to said subject at said therapeutically effective dose;
• and
• (b) a means for iontophoretically delivering said composition at a selected skin site whereby said chemical modifier is cleaved from the complex by a physiological process and said pharmaceutical agent is released within the patient.