The effect of altered urinarypH on the excretion of single doses of orally administered tetracycline hydrochloride and doxycycline hyclate was studied in humans. Alkalinization of the urine significantly enhanced the cumulative renal excretion of both tetracycline and doxycycline as compared to acidic urine treatments. Altered tubular reabsorption was assumed to have caused this effect, since tetracyclines have been shown to be more lipid soluble at their isoelectricpH (approximately thepH of the acidic urine treatment) as compared to more alkalinepHs. The renal clearance of doxycycline was significantly increased by urinary alkalinization.
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