Doxycycline has been considered a safe broad-spectrum antibiotic for patients with renal failure. Although doxycycline possesses many of the metabolic properties of the tetracycline group, toxic blood levels usually do not occur because of the drug’s unique extrarenal route of excretion.
Doxycycline undergoes enterohepatic circulation. Lower levels after food could be because of reduced absorption or reduced enterohepatic cycling. In view of these results, it is advisable to instruct the patients to take doxycycline on an empty stomach.
Doxycycline is almost completely absorbed and is not subject to presystemic metabolism, the mean bioavailability being approximately 93%. Absorption is rapid (effective concentrations are attained as from the first hour), and the peak serum concentration occurs after 2 to 4 hours.