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Relationship between erythrocyte lithium concentration and renal concentrating capacity
S Dashti-Khavidaki1, S A Ahmadi-Abhari, P Ghaeli
1Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. dashtis@sina.tums.ac.ir
Background:
Studies investigating possible correlations between plasma lithium concentration, lithium treatment duration, and frequency of lithium administration, and lithium nephrotoxicity have yielded conflicting results.
Objectives:
Our main objective was to investigate whether there was any relationship between erythrocyte lithium concentration (ELC) and renal side effects. Another objective of our study was to identify a parameter, which could be estimated inexpensively, for assessing possible renal side-effects of lithium.
Method:
Seventy Iranian inpatients with bipolar disorder entered this case-control study. Medications taken concurrently by the patients were recorded. A direct method of measuring ELC was used in this study. The cases were patients on lithium who had urine specific gravity (SG) of 1.006 or less after 8-10 h water deprivation at night and the controls consisted of patients on lithium with urine SG of 1.011 or more after this period. Blood urea nitrogen, serum creatinine, sodium and potassium and urine SG, sodium, and potassium were measured in all patients during this time. Renal indices were compared by using independent sample t-test at a significance level of a P-value of 0.05 or less. Non-parametric Spearman's rank correlation test was used to investigate the relationship between clinical variables and the indices of renal function.
Results:
Results revealed that in case group mean serum sodium concentrations were significantly higher (P = 0.008) and mean urine sodium and potassium were significantly lower than those of controls (P = 0.004 and 0.007 respectively). We found no statistically difference in lithium ratios between the two groups. However, ELCs were significantly higher in the cases (P = 0.026). There were no significant correlation between concomitant use of neuroleptics, benzodiazepines or carbamazepine and ELC or lithium renal side-effects.
Conclusion:
This study showed that ELC may reflect lithium renal side-effects better than plasma lithium level.