Pharmaceutics Drug Disposition Practice Test

The main idea is that the curve’s shape is governed by the balance of how fast the drug is entering the body versus how fast it is being eliminated. When the rate of absorption equals the rate of elimination, the net change in concentration is zero. That moment creates a peak because the concentration cannot rise further as the incoming amount is exactly offset by removal. After that point, elimination dominates and the curve falls.

A horizontal (flat) portion occurs when the input rate matches the output rate continuously, so the concentration stays the same over time—that’s a steady state.

So, both a peak and a horizontal segment indicate the two rates are equal. The best description is that absorption and elimination are equal.