Drug therapy renal changes

Drug therapy individualization for patients with renal insufficiency sometimes requires only a simple proportional dose adjustment based on creatinine clearance (CLcr). Alternatively, complex adjustments are required for drugs that are extensively metabolized or undergo dramatic changes in protein binding and distribution volume. 

Measurement of renal plasma and blood flow is usually reserved for research settings to evaluate hemodynamic changes related to disease or drug therapy. The kidneys receive approximately 20% of cardiac output and representative values of renal blood flow in men and women of about 1200 250 and 1000 180 mL/min per 1.73 w have been reported, respectively. Renal plasma flow (RPF) can be estimated to be 60% of renal blood flow if it is assumed that the average hematocrit is 40%. 

A great deal of information is required in order to interpret drug concentrations correctly. Where concentrations are lower than expected, the most likely cause is non-compliance. In the absence of an increase in dose, higher than expected concentrations indicate that a change has taken place either in other drug therapy or in hepatic or renal function. It is much easierto interpret results if cumulative reports are available, since these allow comparison between levels achieved, provided that dosing details are given. 

Permanent morphological changes in renal structure have been reported in patients who have experienced lithium toxicity (Markowitz et al. 2000). Case reports of irreversible renal failure as a result of chronic, nontoxic lithium therapy are extremely rare and typically foUow 10 or more years of treatment, during which time the patient s serum creatinine levels have gradually increased (e.g., to 2.0 mg/100 mL Gitlin 1993). To minimize the risk of renal complications, which are rare but potentially serious, we recommend frequent patient education about the risks of toxicity and factors that might make toxicity more likely, such as drug interactions or dehy-... 

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