gms | German Medical Science

Background: Medicines are increasingly used in patients with mental disease. Psychoactive drugs are also beneficial in kidney patients. Dialysis patients for example have a significantly increased prevalence of depression. On the other side, the Berlin Initiative Study demonstrated that 50 % of the people older the 70 years have a glomerular filtration rate (GFR) less than 60 ml/min and thus impaired kidney function [1].

Methods: For 71 psychoactive medicines, we have extracted the half-life for normal and failing kidney function from our NEPharm database. If no date were found in the literature for kidney failure, the half-life was estimated for a GFR of 5 % of normal kidney function from the fraction eliminated by the renal route (fren).

T1/2fail = T1/2norm / (1 – fren(1 – GFR%))

The half-life can be used as a marker for the dose and the administration interval since the half-life indicates also the duration of drug action.

Results: One half of the usual psychoactive medicines was found to be eliminated depending on kidney function [2]. For the elderly, drug dose should be based on the “start low, go slow” rule proposed by Jerry Gurwitz. In addition, patients with chronic kidney disease CKD G4 (GFR < 30 ml/min) should not receive more than the half-maximum dosage. Explicit dose recommendations could be derived for 2 of 20 analgesics, 5 of 11 anti-epileptics, 2 of 12 antidepressants, 2 of 11 antipsychotics, 2 of 6 anti-parkinson drugs, 1 of 4 anti-dementive drugs and 1 of 7 benzodiazepines for CKD stage 5 (GFR < 15 ml/min).

Conclusions: Specific dose adjustments must be made for ¼ of all psychoactive substances in CKD stages 4 and 5. In the elderly, the 50-50-50 rule states that 50 % of all psychoactive drugs is eliminated depending on kidney function and 50 % have chronic kidney disease; finally and in doubt, psychoactive medicines should not be administered with more the 50 % of maximum dose in patients above 70 years or a GFR less than 30 ml/min.