first-order release

First-order release is like a draining bathtub: when the tub is full the water rushes out fast, but as the level drops the flow weakens, because the pressure pushing it out depends on how much is left. The release rate is proportional to the amount of drug still in the dosage form.

Because the rate is always a fixed fraction of what remains, release starts brisk and then tapers steadily, never quite reaching zero. Plotting the logarithm of the remaining drug against time gives a straight line, the mathematical fingerprint of a first-order process. Many simple matrix tablets, porous systems, and dissolving products follow this pattern.

First-order release is the natural behaviour of most ordinary controlled-release systems, but it is less ideal than zero order: the early surge raises peak levels while the late tail-off can drop the drug below the effective range. Formulators who want flatter exposure must engineer the system away from pure first-order kinetics toward something closer to constant rate.