Question
Transdermal drug delivery system.
Answer
Transdermal drug delivery systems deliver drug continuously through intact skin into the systemic circulation, bypassing first-pass hepatic metabolism.
Examples: nitroglycerin patch (angina prophylaxis), fentanyl patch (chronic cancer pain), nicotine patch (smoking cessation), scopolamine patch (motion sickness), estrogen patch (hormone replacement).
Advantages: avoids first-pass metabolism, provides steady plasma levels avoiding peak-related toxicity and trough-related loss of efficacy, permits once-daily or longer dosing intervals (improving compliance), and can be discontinued readily by removing the patch if an adverse reaction occurs.
Limitations: only suitable for potent, low-molecular-weight, lipophilic drugs able to cross the skin in adequate quantity; local skin irritation/sensitization at the application site; slow onset, unsuitable for emergencies.