Renal Lithium Elimination in Manic-Depressive Patients – Initial Excretion and Clearance

Prevalence, pathogenesis, and treatment of renal dysfunction associated with chronic lithium therapy

From the analysis of several studies published from 1979 to 1986 comprising 1,172 patients, we estimated that glomerular filtration rate (GFR) was normal in 85% of unselected patients on chronic lithium therapy. The remaining 15% of patients displayed only mild reduction in GFR, clustering at approximately 60 mL/min. Thus, the data available to date do not support earlier concerns that long-term lithium therapy could eventuate into renal insufficiency. The most prevalent renal effect of lithium is impairment of concentrating ability, which we estimated to be present in at least 54% of 1,105 unselected patients on chronic lithium therapy. This defect translated into overt polyuria in only 19% of unselected cases. A renal lesion confined to the collecting tubule has been described in humans who have taken lithium for short periods of time. This lesion may represent the collecting tubule's response to the intracellular accumulation of lithium, which interferes with cAMP formation and results in an early and probably reversible inhibition of antidiuretic hormone (ADH)-mediated water transport. However, long-term lithium therapy may induce a progressive and partly irreversible defect in concentrating ability. The potential risk for dehydration associated with lithium-induced polyuria, as well as the discomfort inherent to this side effect, deserves evaluation and consideration for therapeutic intervention. Amiloride has additional advantages over conventional treatment of nephrogenic diabetes insipidus using thiazide diuretics. The action of amiloride on ADH-mediated water transport seems specific in as much as it is capable of preventing the uptake of lithium in high resistance epithelia and thereby prevents the inhibitory effect of intracellular lithium on water transport. Unlike thiazides, amiloride has a weak natriuretic effect and is less likely to increase plasma lithium levels by causing volume contraction. In addition, amiloride, by conserving potassium, obviates the need for potassium supplementation that is usually required to prevent hypokalemia when thiazides are used to treat lithium-induced polyuria. Since amiloride may prevent chronic intracellular lithium accumulation in the collecting tubule, future studies should elucidate whether amiloride also has a role in preventing lithium-induced chronic tubulo-interstitial damage.

Lithium: long-term effects on the kidney. IV. Renal lithium clearance

Renal lithium clearance was investigated in 44 patients treated with lithium for an average of 8 years as part of a functional-morphological follow-up study including a kidney biopsy. The average renal lithium clearance was 0.36 ml/s (= 21.6 ml/min). A significant correlation with age, sex and glomerular filtration rate was seen, whereas no significant relationship with urine volume, lithium treatment regimen and histopathological biopsy variables was found. The results were compared with the same renal functional tests obtained from a control group consisting of 26 patients with affective disorders never treated with lithium. The control group had a lower urine output, but no significant difference in lithium clearance was observed. In conclusion, renal lithium clearance is a specific investigation, which may provide valuable baseline information on glomerulo-tubular function in patients before and during prophylactic lithium treatment.

Relationship between sodium clearance and proximal tubular fluid output in conscious unoperated rats adapted to different dietary sodium contents

The relationship between the proximal tubular fluid output (Vprox) and the sodium clearance (CNa) was examined in conscious unoperated diabetes insipidus rats adapted to different dietary sodium contents ranging from 5 to 300 mmol/kg. The lithium clearance (CLi) and the urine flow (V) were used as measures of Vprox, CLi being equal to and V being about one-third of Vprox. Variations in the dietary sodium content had almost no influence on CLi and V. However, repeated 2-hour clearance measurements on different days in the same rat showed considerable intraindividual variations of CLi and V, and at each dietary sodium level CNa was linearly correlated to CLi (r = 0.83-0.90) and to V (r = 0.57-0.89). Errors in bladder emptying could not explain these correlations. The slopes of the regression lines increased with increasing dietary sodium content, and the regression lines all intercepted the abscissa at approximately the same value of CLi, i.e. on the average about 40 microliter/min./100 g body weight. The results suggest that Vprox is almost independent of the dietary sodium content. Spontaneous intraindividual variation of Vprox is considerable and is associated with linearly related variation of CNa. The change of CNa for a given change of Vprox increases with the dietary sodium content.

The influence of mania and depression on the pharmacokinetics of lithium. A longitudinal single-case study

A 28-year-old woman, had, every month, a premenstrual manic-depressive cycle beginning with a hypomanic episode followed by a depression which improved with menstruation. The lithium serum level oscillated in a regular and inverse relationship to the mood changes, although the patient received a constant dosage of lithium: 16.2 mmol/l per day. The lithium level reached its highest value at the time of the greatest intensity of depression (1.10 mmol/l), and its lowest value during the time of hypomania (0.30 mmol/l), whereas it showed only small oscillations around 0.5 mmol/l when the patient's mood was normal. RBC lithium concentration and lithium excretion in the urine followed the same pattern. The daily creatinine excretion was usually within normal limits. It must be hypothesized that there are compartments or stores, to and from which lithium is transported, by mechanisms related to the biological basis of mood changes.

Lithium pharmacokinetics: single-dose experiments and analysis using a physiological model

The kinetics of lithium (Li+) distribution after a single dose was studied in healthy human subjects. Experiments were performed by simultaneously following changes of Li+ concentration in plasma, erythrocytes (RBC), and urine. The data were fitted by a simple but physiologically realistic model, so that extracted rate constants could be assigned to real body compartments and compared with independent measurements of cellular transport characteristics. The extracted rate constants were used to calculate steady-state cell-to-plasma Li+ ratios for RBC and for inaccessible cells (mainly muscle). In both cell types, the intracellular Li+ concentration is far below electrochemical equilibrium. This finding suggests that the Li+ countertransport efflux mechanism of RBC may be shared with muscle. We also present evidence for a circadian rhythm in Li+ excretion that parallels the daily cycle of Na+ and K+ excretion.