maintenance dose
The maintenance dose is the regular repeated dose that keeps the drug level parked in the therapeutic zone once it is there. If the loading dose fills the tank, the maintenance dose is the steady trickle that exactly replaces what leaks out, holding the level constant. Its job is to balance ongoing elimination, dose after dose.
Its size is governed by clearance, not by volume of distribution: at steady state the maintenance dosing rate equals clearance times the desired average concentration, adjusted for bioavailability and the dosing interval. Faster clearance demands more frequent or larger maintenance doses to keep pace.
In practice the maintenance dose is split into a convenient interval (once, twice, or several times daily). Shorter intervals give smaller peak-to-trough swings around the same average. Because clearance falls in liver or kidney disease, maintenance doses — far more than loading doses — must be reduced in such patients to avoid accumulation.
After an intravenous aminophylline loading dose, a continuous maintenance infusion is set from the patient's theophylline clearance to hold the level in the therapeutic range.
Maintenance rate is tuned to the patient's clearance.
Maintenance dosing rate = clearance × target concentration / bioavailability. The interval can stay the same in organ impairment while the dose per interval is cut.