National Physical Therapy Examination (NPTE) Practice Exam

A physical therapist assistant is about to apply iontophoresis to a patient. Which of the following equations should be used to determine the correct dosage?

1. current × duration

2. voltage × duration

3. voltage × frequency

4. current × frequency

The correct answer is: voltage × frequency

To determine the correct dosage for iontophoresis, the appropriate equation to use is based on the principles of electrical current and its effect over time. The correct formula is current multiplied by duration. This equation helps quantify the total amount of medication delivered through the skin via the electrical current employed in iontophoresis. In iontophoresis, the dosage is typically expressed in milliamp-minutes (mA-min). The rationale behind using current in the equation is that the amount of drug delivered is directly proportional to the intensity of the current and the duration for which it is applied. This means that increasing either the current or the duration will increase the total amount of medication delivered. Thus, option C represents the fundamental relationship between the electrical current and duration of treatment that physiotherapists need to understand for effective and safe application of iontophoresis.