Renal function clearance

Back S-E, Ljungberg B, Nilsson-Ehle I, Borga O, Nilsson-Ehle P. Age dependence of renal function Clearance of iohexol andp-amino hippurate in healthy males. Scand J Clin Lab Invest 1989 641-6. 

Beierwaltes WH, Harrison-Bernard LM, Sullivan JC, and DL Mattson (2013). Assessment of renal function clearance, the renal microcirculation, renal blood flow, and metabolic balance. Comprehensive Physiology 3(l) 165-200. 

The patient s renal function, evaluated on creatinine clearance ... 

Older adults are at increased risk for adverse reactions from the antineoplastic drugs because of the increased incidence of chronic disease, particularly renal impairment or cardiovascular disease. When renal impairment is present, a lower dosage of the antineoplastic may be indicated. Creatinine clearance isused to monitor renal function in the older adult. Blood creatinine levels are likely to be inaccurate because of a decreased muscle mass in the older adult. 

The study of the mechanism of urinary excretion of amylase and the amylase clearance has been the subject of many studies in recent years. Levitt et. al (79) studied the renal clearance of amylase in renal insufficiency, acute pancreatitis and macro-amylasemia. In acute pancreatitis, the kidney cleared amylase at a markedly increased rate. The ratio of the amylase clearance rate to the creatinine clearance rate (Cgm/Ccr) averaged 3 times normal early in the course of acute pancreatitis, and this elevation could persist after the serum amylase returned to normal. Comparison of an lase clearance to creatinine clearance was to minimize irrelevant changes due to variation in renal function. The increased clearance of amylase makes the urinary amylase a more sensitive indicator of pancreatitis. 

Although most CF patients have shorter half-lives and larger volumes of distribution than non-CF patients, some patients exhibit decreased clearance. Possible causes include concomitant use of nephrotoxic medications, presence of diabetic nephropathy, history of transplantation (with immunosuppressant use and/or procedural hypoxic injury), and age-related decline in renal function in older adult patients. Additionally, CF patients are repeatedly exposed to multiple courses of IV aminoglycosides, which can result in decreased renal function. Evaluation of previous pharmacokinetic parameters and trends, along with incorporation of new health information, is key to providing appropriate dosage recommendations. 

Saline laxatives containing magnesium, potassium, or phosphates should be used cautiously in persons with reduced kidney function. Monitor appropriate serum electrolyte concentrations in patients with unstable renal function evidenced by changing serum creatinine or creatinine clearance. 

The initial dose of allopurinol is based on the patient s renal function. Patients with creatinine clearances of 50 mL/minute or less should receive a starting dose of less than 300 mg/day to minimize adverse effects. The relationship between dose of allopurinol and its most severe side effects is controversial. However, the dose can be adjusted upward as needed and tolerated. It is reasonable to reduce the dose temporarily in patients who develop reversible acute renal failure. 

Probenecid is a uricosuric agent that blocks the tubular reabsorption of uric acid, increasing its excretion. Because of its mechanism of action, probenecid is contraindicated in patients with a history of uric acid stones or nephropathy. Probenecid loses its effectiveness as renal function declines and should be avoided when the creatinine clearance is 50 mL/minute or less. Its uricosuric effect is counteracted by low aspirin doses, which many patients receive for prophylaxis of coronary heart disease. 

Formulas for Estimating Creatinine Clearance in Patients with Stable Renal Function... 

Although determination of creatinine clearance rate is a standard clinical procedure, it is difficult to carry out mainly because accurate collection of total urine output over a 24-hour period is required. It can never be certain that this requirement has been met. Since creatinine is produced continuously in muscle and is cleared by the kidney, renal failure is characterized by elevated serum creatinine levels. The degree of elevation is directly related to the degree of renal failure—if it is assumed that the production of creatinine in the muscle mass is constant and that renal function is stable. When these assumptions are valid, there is a direct relationship between serum creatinine level and kanamycin half-life, as shown in Fig. 9. The equation of the line in Fig. 9 is... 

Renal function can be grossly assessed by hourly measurements of urine output, but estimation of creatinine clearance based on isolated serum creatinine values in critically ill patients may yield erroneous results. Decreased renal perfusion and aldosterone release result in sodium retention and, thus, low urinary sodium (<30 mEq/L). 

TABLE 49-6 Dosing Recommendations for Adult Patients with Reduced Renal Function and for Adult Patients Receiving Hemodialysis Recommended Dose and Frequency for Change in Patients with Creatinine Clearance <30 mL/min ... 

Renal elimination of unchanged drug accounts for 66% of drug clearance, and the dose should be adjusted for impaired renal function. The role of therapeutic drag monitoring is unknown. It has linear pharmacokinetics and is metabolized in blood by nonhepatic enzymatic hydrolysis. 

The ratio (Q) of the estimated elimination rate constant or total body clearance relative to normal renal function is used to determine the dose or dosing interval alterations needed (CLfaii is the clearance with impaired renal function). 

Serum creatinine is not a good measure of renal function in elderly because muscle mass is reduced and the production of creatinine is thus reduced. Estimation of GFR based on serum creatinine is therefore not accurate enough in the elderly (Baracskay et al. 1997). Creatinine clearance should be used instead. Another possibility is measurement of cystatin C in plasma. The rate of production of cystatin C is relatively constant so it seems to be a more reliable estimation of GFR also in older adults. 

Renal function Measurement of effects on urine excretion in saline loaded rats Renal dynamics Measurement of renal blood flow, GFR and clearance... 

From a scientific point of view, glomerular filtration rate (inulin or creatinine clearance) is the best global estimate of renal function. Other parameters of interest include, but are not limited to ... 

Lithium is used in the prophylaxis and treatment of mania and in the prophylaxis of bipolar disorders and recurrent depression. Lithium should be stopped 24 hours before major surgery but the normal dose can be continued for minor surgery, with careful monitoring of fluids and electrolytes. After major surgery, renal function is reduced and this may compromise clearance of lithium. Lithium is a drug with a narrow therapeutic index and it should be avoided if possible in patients with renal impairment. Renal function should be tested before initiating treatment. If lithium is given to patients with renal impairment, a reduced dose should be used and serum lithium concentrations should be monitored closely. 

A plethora of methods has been developed to evaluate renal function by dynamic renography and remote analysis of the excretion of renal function markers. The underlying principle is that the kidneys excrete a majority of small hydrophilic molecules and their clearance, secretion, or fixation in the kidney is quantifiable. When a renal marker in plasma is filtered through the glomeruli, the accumulation of the filtrate in the Bowman s capsule. One or more of the following events may occur in the renal tubule once a marker is filtered or is in plasma [171] ... 

The filtered marker undergoes tubular reabsorption and secretion. The clearance of such markers depends on the relative rates of filtration, reabsorption, and secretion. Determination of renal function by these markers, typified by uric acid, is cumbersome. 

---