Why are intravenous drug dosages easier to control than drugs administered transdermally?

Intravenous drug dosages are indeed easier to control than transdermal drug administrations for several reasons, most notably because the entire dose is delivered directly into the bloodstream. This method ensures that 100% of the drug reaches systemic circulation immediately upon administration, allowing for precise titration and adjustment of dosage based on the patient's needs.

In contrast, transdermal drug delivery involves absorption through the skin, which can introduce variability in how much of the drug actually enters the bloodstream over time. Factors such as skin integrity, blood flow to the skin, and the formulation of the drug can all influence absorption rates. This variability makes it more challenging to predict the effective drug concentration in systemic circulation.

Moreover, while both administration routes need to avoid first-pass metabolism for effective action, this aspect does not directly contribute to the ease of dosage control. The mention of the complexity of dosage forms does not provide a clear advantage for intravenous administration either. Thus, the complete and immediate availability of the drug in the bloodstream is the key reason why intravenous dosages offer easier and more precise control compared to transdermal routes.