Notes & Sources

• Both levels must come from the same dosing interval, drawn after distribution is complete. A level taken during the distribution phase inflates ke and shortens the apparent half-life.
• The elimination constant is derived from the two levels themselves, so the result is specific to this patient rather than to a population estimate. That is the point of the method.
• Extrapolated values assume first-order elimination and a constant interval. They become unreliable in unstable renal function, where levels should simply be repeated.
• The suggested interval is rounded to a practical schedule. Confirm it against the target peak for the organism and the site of infection before applying it.
• Aminoglycoside targets differ substantially between conventional and extended-interval dosing, and between gentamicin, tobramycin and amikacin. Use the target that matches your regimen.