What is the therapeutic index of methylphenidate, given that its ED50 is 10 mg and its TD50 is 30 mg?

The therapeutic index is calculated by dividing the toxic dose (TD50) by the effective dose (ED50). In this case, using the provided values, the therapeutic index for methylphenidate would be calculated as follows:

Therapeutic Index = TD50 / ED50 = 30 mg / 10 mg = 3.

This means that the therapeutic index of 3 indicates that there is a relatively wide margin between the effective dose required to treat the condition (in this case, attention-deficit hyperactivity disorder, or ADHD) and the dose that could potentially cause adverse effects. A therapeutic index greater than 1 suggests that the drug is generally considered safe, as the effective dose is lower than the dose that leads to toxicity.

Understanding the therapeutic index is crucial for clinicians when prescribing medications, as it helps to assess the safety and potential risks associated with a particular drug. A higher therapeutic index can allow for more flexibility in dosing, while a lower index indicates a need for careful monitoring to avoid toxicity. In this context, the calculated therapeutic index of 3 highlights that methylphenidate, when used as indicated, has a reasonable safety margin.