Influence of repetitive dosing and altered urinary pH on doxycycline excretion in humans

The effect of altered urinary pH on the renal excretion of doxycycline, with both single‐ and multiple‐dose regimens, was studied in humans. Alkalinization of the urine resulted in higher cumulative amounts of doxycycline excreted during both single and multiple‐dose regimens. The increased excretion was reflected in larger renal clearances and shorter half‐lives for both regimens when the alkaline condition was compared to the control condition. Half‐life values increased from the single‐ to the multiple‐dose regimen under both alkaline and control conditions. However, the increase in half‐life values from single‐ to multiple‐dose administration under the alkaline condition was shorter than the half‐life change under control conditions.