[The pharmacokinetics of doxycycline in kidney insufficiency in geriatric patients compared to younger adults].

In young adults i.v. injection of 200 mg doxycycline was followed by a rapid fall in serum levels in the first 30 minutes and than a slow decrease (serum concentration after 24 h on average 1.0 mug/ml). Biological half-life was 11.9 h, final distribution volume 50.0 litres and urine recovery 70%. After oral administration of 200 mg doxycycline the serum peaks measured were 3.4 mug/ml (2 1/2 h later). With repeated doses of 100 mg every 24 h serum peaks were 2.8 mug/ml and serum concentrations after 24 h 0.8-0.9 mug/ml (urine recovery 43%). The area under the curve was 25.5% less than after i.v. injection. In 7 adults with chronic renal failure the half-life of doxycycline varied between 10 and 24 h. With repeated oral administration of doxycycline (100 mg every 24 h) there was no accumulation of the drug in blood. During hemodialysis (Stuttgart kidneys, Rhône-Poulenc plates) doxycycline injected i.v. was eliminated as rapidly as before. In renal failure doxycycline may be given in the same dosage as where renal function is normal. In 12 geriatric patients without renal disease, serum levels of doxycycline after i.v. injection of 200 mg were not significantly different from those of young adults (distribution volume 46.2 +/- 16.2 litres). It can therefore be assumed that tissue penetration of the drug is similar in the elderly and in young adults.