Use of stabilized inverse propensity scores as weights to directly estimate relative risk and its confidence intervals

OBJECTIVES

Inverse probability of treatment weighting (IPTW) has been used in observational studies to reduce selection bias. For estimates of the main effects to be obtained, a pseudo data set is created by weighting each subject by IPTW and analyzed with conventional regression models. Currently, variance estimation requires additional work depending on type of outcomes. Our goal is to demonstrate a statistical approach to directly obtain appropriate estimates of variance of the main effects in regression models.

METHODS

We carried out theoretical and simulation studies to show that the variance of the main effects estimated directly from regressions using IPTW is underestimated and that the type I error rate is higher because of the inflated sample size in the pseudo data. The robust variance estimator using IPTW often slightly overestimates the variance of the main effects. We propose to use the stabilized weights to directly estimate both the main effect and its variance from conventional regression models.

RESULTS

We applied the approach to a study examining the effectiveness of serum potassium monitoring in reducing hyperkalemia-associated adverse events among 27,355 diabetic patients newly prescribed with a renin-angiotensin-aldosterone system inhibitor. The incidence rate ratio (with monitoring vs. without monitoring) and confidence intervals were 0.46 (0.34, 0.61) using the stabilized weights compared with 0.46 (0.38, 0.55) using typical IPTW.

CONCLUSIONS

Our theoretical, simulation results and real data example demonstrate that the use of the stabilized weights in the pseudo data preserves the sample size of the original data, produces appropriate estimation of the variance of main effect, and maintains an appropriate type I error rate.

Drug-drug interactions among elderly patients hospitalized for drug toxicity

CONTEXT

Drug-drug interactions are a preventable cause of morbidity and mortality, yet their consequences in the community are not well characterized.

OBJECTIVE

To determine whether elderly patients admitted to hospital with specific drug toxicities were likely to have been prescribed an interacting drug in the week prior to admission.

DESIGN

Three population-based, nested case-control studies.

SETTING

Ontario, Canada, from January 1, 1994, to December 31, 2000.

PATIENTS

All Ontario residents aged 66 years or older treated with glyburide, digoxin, or an angiotensin-converting enzyme (ACE) inhibitor. Case patients were those admitted to hospital for drug-related toxicity. Prescription records of cases were compared with those of controls (matched on age, sex, use of the same medication, and presence or absence of renal disease) for receipt of interacting medications (co-trimoxazole with glyburide, clarithromycin with digoxin, and potassium-sparing diuretics with ACE inhibitors).

MAIN OUTCOME MEASURE

Odds ratio for association between hospital admission for drug toxicity (hypoglycemia, digoxin toxicity, or hyperkalemia, respectively) and use of an interacting medication in the preceding week, adjusted for diagnoses, receipt of other medications, the number of prescription drugs, and the number of hospital admissions in the year preceding the index date.

RESULTS

During the 7-year study period, 909 elderly patients receiving glyburide were admitted with a diagnosis of hypoglycemia. In the primary analysis, those patients admitted for hypoglycemia were more than 6 times as likely to have been treated with co-trimoxazole in the previous week (adjusted odds ratio, 6.6; 95% confidence interval, 4.5-9.7). Patients admitted with digoxin toxicity (n = 1051) were about 12 times more likely to have been treated with clarithromycin (adjusted odds ratio, 11.7; 95% confidence interval, 7.5-18.2) in the previous week, and patients treated with ACE inhibitors admitted with a diagnosis of hyperkalemia (n = 523) were about 20 times more likely to have been treated with a potassium-sparing diuretic (adjusted odds ratio, 20.3; 95% confidence interval, 13.4-30.7) in the previous week. No increased risk of drug toxicity was found for drugs with similar indications but no known interactions (amoxicillin, cefuroxime, and indapamide, respectively).

CONCLUSIONS

Many hospital admissions of elderly patients for drug toxicity occur after administration of a drug known to cause drug-drug interactions. Many of these interactions could have been avoided.

Patiromer in patients with kidney disease and hyperkalemia receiving RAAS inhibitors

BACKGROUND

Hyperkalemia increases the risk of death and limits the use of inhibitors of the renin-angiotensin-aldosterone system (RAAS) in high-risk patients. We assessed the safety and efficacy of patiromer, a nonabsorbed potassium binder, in a multicenter, prospective trial.

METHODS

Patients with chronic kidney disease who were receiving RAAS inhibitors and who had serum potassium levels of 5.1 to less than 6.5 mmol per liter received patiromer (at an initial dose of 4.2 g or 8.4 g twice a day) for 4 weeks (initial treatment phase); the primary efficacy end point was the mean change in the serum potassium level from baseline to week 4. Eligible patients at the end of week 4 (those with a baseline potassium level of 5.5 to <6.5 mmol per liter in whom the level decreased to 3.8 to <5.1 mmol per liter) entered an 8-week randomized withdrawal phase in which they were randomly assigned to continue patiromer or switch to placebo; the primary efficacy end point was the between-group difference in the median change in the serum potassium level over the first 4 weeks of that phase.

RESULTS

In the initial treatment phase, among 237 patients receiving patiromer who had at least one potassium measurement at a scheduled visit after day 3, the mean (±SE) change in the serum potassium level was -1.01±0.03 mmol per liter (P<0.001). At week 4, 76% (95% confidence interval, 70 to 81) of the patients had reached the target potassium level (3.8 to <5.1 mmol per liter). Subsequently, 107 patients were randomly assigned to patiromer (55 patients) or placebo (52 patients) for the randomized withdrawal phase. The median increase in the potassium level from baseline of that phase was greater with placebo than with patiromer (P<0.001); a recurrence of hyperkalemia (potassium level, ≥5.5 mmol per liter) occurred in 60% of the patients in the placebo group as compared with 15% in the patiromer group through week 8 (P<0.001). Mild-to-moderate constipation was the most common adverse event (in 11% of the patients); hypokalemia occurred in 3%.

CONCLUSIONS

In patients with chronic kidney disease who were receiving RAAS inhibitors and who had hyperkalemia, patiromer treatment was associated with a decrease in serum potassium levels and, as compared with placebo, a reduction in the recurrence of hyperkalemia. (Funded by Relypsa; OPAL-HK ClinicalTrials.gov number, NCT01810939.).

The frequency of hyperkalemia and its significance in chronic kidney disease

BACKGROUND

Hyperkalemia is a potential threat to patient safety in chronic kidney disease (CKD). This study determined the incidence of hyperkalemia in CKD and whether it is associated with excess mortality.

METHODS

This retrospective analysis of a national cohort comprised 2 103 422 records from 245 808 veterans with at least 1 hospitalization and at least 1 inpatient or outpatient serum potassium record during the fiscal year 2005. Chronic kidney disease and treatment with angiotensin-converting enzyme inhibitors and/or angiotensin II receptor blockers (blockers of the renin-angiotensin-aldosterone system [RAAS]) were the key predictors of hyperkalemia. Death within 1 day of a hyperkalemic event was the principal outcome.

RESULTS

Of the 66 259 hyperkalemic events (3.2% of records), more occurred as inpatient events (n = 34 937 [52.7%]) than as outpatient events (n = 31 322 [47.3%]). The adjusted rate of hyperkalemia was higher in patients with CKD than in those without CKD among individuals treated with RAAS blockers (7.67 vs 2.30 per 100 patient-months; P < .001) and those without RAAS blocker treatment (8.22 vs 1.77 per 100 patient-months; P < .001). The adjusted odds ratio (OR) of death with a moderate (potassium, >or=5.5 and <6.0 mEq/L [to convert to mmol/L, multiply by 1.0]) and severe (potassium, >or=6.0 mEq/L) hyperkalemic event was highest with no CKD (OR, 10.32 and 31.64, respectively) vs stage 3 (OR, 5.35 and 19.52, respectively), stage 4 (OR, 5.73 and 11.56, respectively), or stage 5 (OR, 2.31 and 8.02, respectively) CKD, with all P < .001 vs normokalemia and no CKD.

CONCLUSIONS

The risk of hyperkalemia is increased with CKD, and its occurrence increases the odds of mortality within 1 day of the event. These findings underscore the importance of this metabolic disturbance as a threat to patient safety in CKD.

Sodium zirconium cyclosilicate in hyperkalemia

BACKGROUND

Hyperkalemia (serum potassium level, >5.0 mmol per liter) is associated with increased mortality among patients with heart failure, chronic kidney disease, or diabetes. We investigated whether sodium zirconium cyclosilicate (ZS-9), a novel selective cation exchanger, could lower serum potassium levels in patients with hyperkalemia.

METHODS

In this multicenter, two-stage, double-blind, phase 3 trial, we randomly assigned 753 patients with hyperkalemia to receive either ZS-9 (at a dose of 1.25 g, 2.5 g, 5 g, or 10 g) or placebo three times daily for 48 hours. Patients with normokalemia (serum potassium level, 3.5 to 4.9 mmol per liter) at 48 hours were randomly assigned to receive either ZS-9 or placebo once daily on days 3 to 14 (maintenance phase). The primary end point was the exponential rate of change in the mean serum potassium level at 48 hours.

RESULTS

At 48 hours, the mean serum potassium level had decreased from 5.3 mmol per liter at baseline to 4.9 mmol per liter in the group of patients who received 2.5 g of ZS-9, 4.8 mmol per liter in the 5-g group, and 4.6 mmol per liter in the 10-g group, for mean reductions of 0.5, 0.5, and 0.7 mmol per liter, respectively (P<0.001 for all comparisons) and to 5.1 mmol per liter in the 1.25-g group and the placebo group (mean reduction, 0.3 mmol per liter). In patients who received 5 g of ZS-9 and those who received 10 g of ZS-9, serum potassium levels were maintained at 4.7 mmol per liter and 4.5 mmol per liter, respectively, during the maintenance phase, as compared with a level of more than 5.0 mmol per liter in the placebo group (P<0.01 for all comparisons). Rates of adverse events were similar in the ZS-9 group and the placebo group (12.9% and 10.8%, respectively, in the initial phase; 25.1% and 24.5%, respectively, in the maintenance phase). Diarrhea was the most common complication in the two study groups.

CONCLUSIONS

Patients with hyperkalemia who received ZS-9, as compared with those who received placebo, had a significant reduction in potassium levels at 48 hours, with normokalemia maintained during 12 days of maintenance therapy. (Funded by ZS Pharma; ClinicalTrials.gov number, NCT01737697.).

Selective aldosterone blockade with eplerenone reduces albuminuria in patients with type 2 diabetes

Previous studies have shown that the selective aldosterone blocker eplerenone, in doses of up to 200 mg/d, reduces albuminuria in patients with type 2 diabetes. This study was conducted to ascertain whether lower doses of eplerenone (50 or 100 mg/d) co-administered with the angiotensin-converting enzyme (ACE) inhibitor enalapril would produce a similar antialbuminuric effect while obviating the hyperkalemia observed previously. After open-label run-in with enalapril 20 mg/d, patients with diabetes and a urinary albumin:creatinine ratio (UACR) > or = 50 mg/g were randomly assigned to receive enalapril plus one of three double-blind daily treatments for 12 wk: placebo, eplerenone 50 mg (EPL50), or eplerenone 100 mg (EPL100). After week 4, amlodipine 2.5 to 10 mg/d was allowed for BP control (systolic/diastolic BP < or = 130/80 mmHg). The primary study end points were the percentage change from baseline at week 12 in UACR and the incidence of hyperkalemia. Secondary end points included percentage changes from baseline in UACR at weeks 4 and 8 and changes from baseline in systolic and diastolic BP. Treatment with EPL50 or EPL100 but not placebo significantly reduced albuminuria from baseline. By week 12, UACR was reduced by 7.4% in the placebo group, by 41.0% in the EPL50 group, and by 48.4% in the EPL100 group (both eplerenone groups, P < 0.001 versus placebo). The incidences of sustained and severe hyperkalemia were not significantly different in any of the three treatment arms and did not differ on the basis of quartile of estimated GFR (all NS). For the secondary end points, both eplerenone treatment groups significantly reduced albuminuria from baseline as early as week 4 (P < 0.001), whereas placebo treatment (including enalapril) did not result in any significant decreases in UACR. Systolic BP decreased significantly in all treatment groups at all time points, but, generally, all treatment groups experienced similar decreases in BP. Co-administration of EPL50 or EPL100 with an ACE inhibitor as compared with an ACE inhibitor alone significantly reduces albuminuria in patients with diabetes without producing significant increases in hyperkalemia.

Acute tumor lysis syndrome. A review of 37 patients with Burkitt's lymphoma

Renal and metabolic complications of tumor lysis during 46 episodes of remission induction chemotherapy were reviewed in 37 patients with American Burkitt's lymphoma. Azotemia occurred in 14 patients, preceding chemotherapy in eight. All of these patients had abdominal tumors. Pretreatment azotemia was associated with elevated lactic dehydrogenase (LDH) and uric acid levels, and sometimes extrinsic ureteral obstruction by tumor. Two patients required dialysis for uric acid nephropathy before chemotherapy was initiated. Following chemotherapy, major complications of tumor lysis (hyperuricemia, hyperkalemia and hyperphosphatemia) were associated with very large tumors, high LDH levels and inadequate urinary output. In patients undergoing diuresis and receiving allopurinol, hyperkalemia or hyperuricemia developed infrequently unless concomitant renal failure ensued. Hyperphosphatemia, which occurred only after chemotherapy, developed in 10 of 32 (31 per cent) nonazotemic and in all azotemic patients. Hemodialysis was required in three post-treatment patients for control of azotemia, hyperuricemia, hyperphosphatemia and/or hyperkalemia. Because of the potential for renal failure caused by precipitation of phosphate, severe hyperphosphatemia is an additional criterion for dialysis in patients with acute tumor lysis syndrome.

Safe and effective inhibition of renal uptake of radiolabelled octreotide by a combination of lysine and arginine

As scintigraphy with [(111)In-DTPA(0)]octreotide has become a standard technique in analysing somatostatin receptor-receptor positive lesions such as neuroendocrine tumours, a logical next step is peptide receptor radionuclide therapy (PRRT). Initial studies on PRRT were performed with high doses of [(111)In-DTPA(0)]octreotide, and recently other radionuclides coupled to other somatostatin analogues have been used for this purpose. However, the dose delivered to the kidney is a major dose-limiting factor. Amino acid solutions have previously been used to reduce renal uptake of radioactivity, but these solutions have some disadvantages, i.e. their hyperosmolarity and their propensity to cause vomiting and metabolic changes. In this study we tested various amino acid solutions in patients receiving [(111)In-DTPA(0)]octreotide PRRT in order to assess their safety and their capacity to inhibit the renal uptake of radioactivity. Patients served as their own non-infused control. Renal radioactivity at 24 h following the injection of [(111)In-DTPA(0)]octreotide was inhibited by (1) a commercially available amino acid solution (AA) (21%+/-14%, P<0.02), (2) by 25 g (17%+/-9%, P<0.04), 50 g (15%+/-13%, P<0.04) or 75 g of lysine (44%+/-11%, P<0.001) and (3) by a combination of 25 g of lysine plus 25 g of arginine (LysArg) (33%+/-23%, P<0.01). Fluid infusion alone (500, 1,000 or 2,000 ml of saline/glucose) did not change renal uptake of radioactivity. In patients studied with 75 g of lysine (Lys75) and LysArg, serum potassium levels rose significantly. Maximal potassium levels were within the toxic range (6.3, 6.7 and 6.8 mmol/l) in three out of six patients infused with Lys75, whereas with LysArg the highest concentration measured was 6.0 mmol/l. Electrocardiographic analysis did not reveal significant changes in any of the patients. Vomiting occurred in 50% of patients infused with AA, but in only 6% of patients receiving no amino acid infusion (controls) and 9% of patients receiving LysArg. We conclude that co-infusion of Lys75 or LysArg results in a significant inhibition of renal radioactivity in PRRT, allowing higher treatment doses and thus resulting in higher tumour radiation doses. Because Lys75 produced serious hyperkalaemia, it is not suitable for clinical use. LysArg, however, is effective in offering renal protection in PRRT and is safe.

Complications of inappropriate use of spironolactone in heart failure: when an old medicine spirals out of new guidelines

OBJECTIVES

This study was designed to investigate the appropriateness and complications of the use of spironolactone for heart failure (HF) in clinical practice.

BACKGROUND

Spironolactone was reported by one prospective randomized trial to decrease morbidity and mortality in patients with New York Heart Association (NYHA) class III and IV HF. With this report (Randomized Spironolactone Evaluation Study [RALES] trial), we noted a marked increase in widespread use of spironolactone in patients with HF. Long-term outcome data with respect to safety and utilization of this medication in HF are not available.

METHODS

To investigate the use of spironolactone for HF in a clinical setting, we analyzed the application of the RALES trial protocol to the care of 104 patients, whom we identified as being started on spironolactone for HF after prerelease of the RALES trial.

RESULTS

We found broader use, less intensive follow-up, and increased complications with spironolactone treatment compared with the RALES trial. Cardiologists provided more appropriate care than did primary care providers.

CONCLUSIONS

These data suggest that spironolactone is being used widely in HF without consideration of the NYHA class and ejection fraction, and without optimization of background treatment with angiotensin-converting enzyme inhibitors and beta-blockers. Clinical follow-up does not adhere to the RALES trial guidelines, resulting in higher complications. We conclude that long-term studies with further safety and efficacy data are needed.

Hyperkalemia in hospitalized patients: causes, adequacy of treatment, and results of an attempt to improve physician compliance with published therapy guidelines

BACKGROUND

Hyperkalemia is a common, potentially life-threatening disorder. Electrocardiograms are considered to be sensitive indicators of the presence of hyperkalemia. Since the treatment of hyperkalemia involves relatively few maneuvers and because its success can be objectively scored, we investigated how physicians manage this disorder and how successful their prescribed therapy is. We also sought to determine whether treatment could be improved by providing the treating physicians with therapy guidelines on a real-time basis.

METHODS

Consecutive patients with hyperkalemia were identified by review of laboratory records. During the observation-only phase of the study, demographic data, contributing causes, electrocardiogram findings, treatments used, compliance with prescribing guidelines, and patient outcome were recorded. During the subsequent notification phase of the study, treatment recommendations were sent to the patient's ward when the elevated potassium value was noted. The same outcome data were collected.

RESULTS

There were 127 episodes of hyperkalemia during the observation-only phase and 115 during the notification phase. No patients died or had life-threatening cardiac arrhythmias. Electrocardiographic abnormalities consistent with hyperkalemia were observed in only 14% of episodes. Renal failure (77%), drugs (63%), and hyperglycemia (49%) contributed to most episodes. Treatments used were exchange resin (51%), insulin (46%), calcium (36%), bicarbonate (34%), and albuterol (4%). The agents were equally efficacious. The time to first treatment was shorter in patients with potassium levels of 6.5 mmol/L or more than in patients with lower values (2.1 +/- 2.2 vs 2.8 +/- 2.4 hours; P<.05). Treatment was better in the intensive care unit than on regular wards. Only 39% of episodes during the observation-only period met the predetermined criteria for monitoring and diagnosis, initial treatment, and follow-up. During the notification period, physician performance was no better; only 42% of episodes met all criteria. The laboratory transmitted a copy of the guidelines to the patient's ward only 38% of the time. In a separate analysis of these episodes, there was no improvement in treatment. Physicians who did not receive the notification fulfilled all treatment criteria more often than physicians who did (50% vs 30%; P<.05).

CONCLUSIONS

Although treatment of hyperkalemia was frequently suboptimal, no serious arrhythmias and no deaths complicated management of 242 episodes of severe hyperkalemia. A narrowly targeted effort to improve physician management of a disorder with discrete treatment options did not improve therapy.

Acute renal failure due to nontraumatic rhabdomyolysis

Twenty-one patients developed acute renal failure in association with nontraumatic rhabdomyolysis and myoglobinuria. The illness followed an overdose of ethanol, heroin, or other depressant drug in 18 patients. Lethargy or coma was present in 17 patients and muscle swelling in 11. Evidence of rhabdomyolysis included markedly elevated creatine phosphokinase, myoglobinuria, and aldolase in blood. Initial biochemical findings were similar to those of acute renal failure due to other causes, but the abnormalities were exaggerated. There was a disproportionate rise in serum creatinine concentration in relation to serum urea nitrogen concentration. Profound hyperuricemia was present in most patients. Transient hypercalcemia developed during the diuretic phase in 5 patients. One patient died. We conclude that nontraumatic myoglobinuria with acute renal failure is not infrequent and may occur after an overdose of ethanol or heroin. The disease has good prognosis despite severe hypercatbolism and untreated profound hyperuricemia.

Acute tumor lysis syndrome in patients with high-grade non-Hodgkin's lymphoma

PURPOSE

To identify patients with lymphoma at risk for tumor lysis after chemotherapy.

PATIENTS AND METHODS

The case records of 102 patients receiving combination chemotherapy for non-Hodgkin's lymphoma (intermediate to high-grade histology) were reviewed. Patients were considered to have "laboratory tumor lysis" if two of the following metabolic changes occurred within 4 days of treatment: a 25% increase in the serum phosphate, potassium, uric acid, or urea nitrogen concentrations, or a 25% decline in the serum calcium concentration. "Clinical tumor lysis" was defined as laboratory tumor lysis plus one of the following: a serum potassium level greater than 6 mmol/L, a creatinine level greater than 221 mumol/L, or a calcium level less than 1.5 mmol/L, the development of a life-threatening arrhythmia, or sudden death.

RESULTS

Laboratory tumor lysis occurred in 42% of patients and clinical tumor lysis in 6%. There was no statistical difference in the frequency of either tumor lysis syndrome among lymphoma subgroups. Clinical tumor lysis occurred more frequently in patients with pretreatment renal insufficiency (serum creatinine level greater than 132 mumol/L) than in patients with normal renal function (36% versus 2%; p = 0.01). The development of azotemia correlated with high pretreatment serum lactate dehydrogenase concentrations (p < 0.01; r2 = 0.11).

CONCLUSION

Clinically significant tumor lysis is a rare occurrence in patients with lymphoma when they are receiving allopurinol. However, tumor lysis can occur in patients with all types of moderate to high-grade non-Hodgkin's lymphoma. Patients with a high serum lactate dehydrogenase level or renal insufficiency are at increased risk for metabolic complications after chemotherapy and should be closely monitored.

Adrenergic modulation of extrarenal potassium disposal

We studied the role of catecholamines in the regulation of potassium homeostasis in nine healthy subjects given intravenous potassium chloride (0.5 meq per kilogram of body weight) in the presence and absence of propranolol. Potassium infusion elevated serum potassium 0.6 +/- 0.09 meq per liter (mean +/-S.E.M.). Addition of propranolol augmented the rise (0.9 +/- 0.05 meq per liter) and prolonged the elevation in serum potassium without decreasing urinary potassium excretion. In a separate study, the same potassium load was administered with a concomitant infusion of epinephrine in five subjects. Epinephrine markedly blunted the increment in serum potassium (0.1 +/- 0.06 meq per liter) while reducing renal potassium excretion. Plasma aldosterone was not altered by the experimental procedures. Serum insulin fell minimally in the presence of propranolol but was unaffected by epinephrine. beta-Adrenergic blockade impairs and epinephrine enhances extrarenal disposal of an acute potassium load. These findings suggest that in patients with impaired potassium disposal, the risk of hyperkalemia may be increased when sympathetic blockade is induced.

The syndrome of rhabdomyolysis: complications and treatment

Rhabdomyolysis is a syndrome of skeletal muscle cell damage that leads to the release of toxic intracellular material into the systemic circulation. The pathogenesis of rhabdomyolysis is based on an increase in free ionized calcium in the cytoplasm. Its main complications include (a) acute renal failure, which is triggered by renal vasoconstriction and ischemia, (b) myoglobin cast formation in the distal convoluted tubules, and (c) direct renal toxic effect of myoglobin on the epithelial cells of proximal convoluted tubules. Other major complications include electrolyte disorders, such as hyperkalemia, which may cause cardiac arrhythmias, metabolic acidosis, hyperphosphatemia, early hypocalcemia, and late hypercalcemia. Compartmental syndrome and disseminated intravascular coagulopathy may also emerge. The management of myoglobinuric acute renal failure includes aggressive fluid administration to restore the hypovolemia and urine alkalization. The concomitant electrolyte and metabolic disorders should also be treated appropriately; hemodialysis should be considered when life-threatening hyperkalemia and metabolic acidosis exist. In the case of compartmental syndrome, it is important to monitor the intra-compartmental pressure and to perform fasciotomy, if required. When diagnosed early and if the appropriate treatment is initiated promptly, the complications of rhabdomyolysis are preventable and the syndrome has a good prognosis.

Mineralocorticoid-resistant renal hyperkalemia without salt wasting (type II pseudohypoaldosteronism): role of increased renal chloride reabsorption

A rare syndrome has been described in which mineralocorticoid-resistant hyperkalemia of renal origin occurs in the absence of glomerular insufficiency and renal sodium wasting and in which hyperchloremic acidosis, hypertension, and hyporeninemia coexist. The primary abnormality has been postulated to be a defect of the potassium secretory mechanism of the distal nephron. The present studies were carried out to investigate the mechanism of impaired renal potassium secretion in a patient with this syndrome. When dietary intake of sodium chloride was normal, renal clearance of potassium was subnormal (CK/GFR = 3.6 +/- 0.2%; normal subjects, 9.0 +/- 0.9%, N = 4) despite high normal or supernormal levels of plasma and urinary aldosterone. The fractional clearance of potassium remained subnormal (CK/GFR = 5.1 +/- 0.2%) during superimposed chronic administration of superphysiologic doses of mineralocorticoid hormone. Little increase in renal potassium clearance occurred when the delivery of sodium to distal nephron segments was increased further by the i.v. infusion of sodium chloride, despite experimentally sustained hypermineralocorticoidism. But potassium clearance increased greatly when delivery of sodium to the distal nephron was increased by infusion of nonchloride anions: sulfate (sodium sulfate infusion, low sodium chloride diet; CK/GFR = 63.7 +/- 0.4%) or bicarbonate (sodium bicarbonate plus acetazolamide infusion; CK/GFR = 81.7 +/- 1.7%). These findings indicate that mineralocorticoid-resistant renal hyperkalemia in this patient cannot be attributed to the absence of a renal potassium secretory capability or to diminished delivery of sodium to distal nephron segments; instead it may be dependent on chloride delivery to the distal nephron. We suggest that the primary abnormality in this syndrome increases the reabsorptive avidity of the distal nephron for chloride, which (1) limits the sodium and mineralocorticoid-dependent voltage driving force for potassium and hydrogen ion secretion, resulting in hyperkalemia and acidosis and (2) augments distal sodium chloride reabsorption resulting in hyperchloremia, volume expansion, hyporeninemia, and hypertension.

Hyperkalemic distal renal tubular acidosis associated with obstructive uropathy

We studied renal function in 13 patients with obstructive uropathy and hyperkalemic metabolic acidosis to characterize the pathogenesis of this disorder. Base-line fractional potassium excretion was lower in all patients than in controls with similar glomerular filtration rates. Acetazolamide was given to 11 patients but failed to increase fractional potassium excretion to normal. In five patients, impaired potassium excretion was associated with decreased ammonium excretion, a urinary pH below 5.5 (5.18 +/- 0.07, mean +/- S.E.M.), and aldosterone deficiency. In the remaining eight patients, the urinary pH did not fall below 5.5 (6.4 +/- 0.2) with acidosis, and we failed to lower the urinary pH and increase fractional potassium excretion to normal by administering a mineralocorticoid and sodium sulfate. A syndrome of hyperkalemic distal renal tubular acidosis may occur in patients with obstructive uropathy. In some patients, this syndrome results from a defect in hydrogen and potassium secretion in the distal nephron rather than from aldosterone deficiency. Obstructive uropathy should be included in the differential diagnosis of hyperkalemic acidosis and renal insufficiency.

Effect of various therapeutic approaches on plasma potassium and major regulating factors in terminal renal failure

PURPOSE

The development of life-threatening hyperkalemia poses a risk for patients with chronic preterminal renal failure. Various therapeutic options have been suggested for hyperkalemic emergencies in these patients; to date, however, no study has evaluated the relative efficacies of these measures in the presence of renal failure. Our goal was to examine the acute effects of a variety of therapeutic approaches, as well as those of hemodialysis, on plasma potassium levels in a hemodialysis population.

PATIENTS AND METHODS

Ten patients with terminal renal failure undergoing maintenance hemodialysis were enrolled in the study. Blood gas parameters and plasma sodium, potassium, glucose, osmolality, renin, aldosterone, epinephrine, norepinephrine, dopamine, and insulin were measured before, during, and after 60-minute infusions of bicarbonate, epinephrine, and insulin in glucose, and before, during, and after performance of regular hemodialysis for one hour.

RESULTS

Hypertonic as well as isotonic intravenous bicarbonate (2 to 4 mmol/minute) induced a marked rise in plasma bicarbonate and pH, but failed to lower the plasma potassium level (5.66 versus 5.83 mmol/liter before and after). Epinephrine, 0.05 microgram/kg/minute administered intravenously, decreased plasma potassium only slightly from 5.57 to 5.25 mmol/liter, and five patients showed no decline. On the other hand, insulin in glucose, 5 mU/kg/minute intravenously, effectively lowered plasma potassium levels from 5.62 to 4.70 mmol/liter, and hemodialysis induced the most rapid decline from 5.63 to 4.29 mmol/liter. Plasma aldosterone was elevated before treatment; it correlated with plasma potassium and dropped during intravenous bicarbonate administration or hemodialysis. Pretreatment plasma renin activity, insulin, epinephrine, norepinephrine, and dopamine levels were generally normal.

CONCLUSION

We conclude that in patients with terminal renal failure undergoing maintenance hemodialysis, intravenous bicarbonate is ineffective in lowering plasma potassium rapidly, and epinephrine is effective in only half the patients, whereas insulin in glucose is a fast and reliable form of therapy for hyperkalemic emergencies. Plasma aldosterone levels are appropriate in relationship to plasma potassium levels, and levels of other potassium-influencing hormones are generally normal.

Tumor lysis syndrome: new challenges and recent advances

Tumor lysis syndrome (TLS) is an oncologic emergency triggered by the rapid release of intracellular material from lysing malignant cells. Most common in rapidly growing hematologic malignancies, TLS has been reported in virtually every cancer type. Central to its pathogenesis is the rapid accumulation of uric acid derived from the breakdown of nucleic acids, which leads to kidney failure by various mechanisms. Kidney failure then limits the clearance of potassium, phosphorus, and uric acid leading to hyperkalemia, hyperphosphatemia, and secondary hypocalcemia, which can be fatal. Prevention of TLS may be more effective than treatment, and identification of at-risk individuals in whom to target preventative efforts remains a key research area. Herein, we discuss the pathophysiology, epidemiology, and treatment of TLS with an emphasis on the kidney manifestations of the disease.

A single institution, randomized, prospective trial of cyclosporin versus azathioprine-antilymphocyte globulin for immunosuppression in renal allograft recipients

Between September 26, 1980 and December 31, 1983, 230 splenectomized, transfused renal allograft recipients were randomized to treatment with either cyclosporin-prednisone (N = 121, 68 diabetic and 53 nondiabetic recipients; 73 cadaver and 48 related donor grafts) or azathioprine-prednisone-antilymphocyte globulin (N = 109, 61 diabetic and 48 nondiabetic recipients; 69 cadaver and 40 related donor grafts). The results were analyzed on March 31, 1984. Actuarial patient survival rates at 2 years were 88% in the cyclosporin and 91% in the azathioprine groups (p = 0.649). Graft survival rates at 2 years were 82% in all cyclosporin and 77% in all azathioprine-treated recipients (p = 0.150); the corresponding figures in the recipients of related donor grafts were 87% vs. 83% (p = 0.656), and in the recipients of cadaver donor grafts were 78% vs. 73% (p = 0.178). The 2-year graft survival rates were 81% in cyclosporin and 74% in azathioprine-treated diabetic recipients (p = 0.150) and 83% in cyclosporin and 81% in azathioprine-treated nondiabetic recipients (p = 0.604). Within the cyclosporin and azathioprine treatment groups, the differences in graft survival rates between diabetic and nondiabetic recipients were not significant (p = 0.822 and 0.423, respectively). Although there were no significant differences in graft survival rates, the cumulative incidence of rejection episodes within the first post-transplant year was significantly lower in the cyclosporin (34%) than in the azathioprine (60%) treated recipients (p = 0.001). In recipients of technically successful cadaver kidney grafts, the incidence of acute tubular necrosis (ATN) was 31% in cyclosporin and 30% in azathioprine-treated recipients (p = 0.822). Graft survival rates in azathioprine- and cyclosporin-treated recipients who did or did not undergo ATN were 72% vs. 89% (p = 0.011). The mean (+/- S.D.) serum creatinine levels (mg/dl) at 1 year were higher in cyclosporin (2.0 +/- 0.6) than in azathioprine (1.5 +/- 0.5) treated recipients (p = less than 0.001). A reduction in cyclosporin dose because of nephrotoxicity was required in 96 of the cyclosporin-treated patients (70%), and 25 were switched to treatment with azathioprine (21%). The incidence of all infections in cyclosporin-treated patients was approximately half of that in azathioprine-treated patients, and only nine per cent of the cyclosporin-treated patients were diagnosed to have cytomegalovirus infections during the first post-transplant year vs. 28% in azathioprine-treated patients (p = 0.002).(ABSTRACT TRUNCATED AT 400 WORDS)

Necrosis of the gastrointestinal tract in uremic patients as a result of sodium polystyrene sulfonate (Kayexalate) in sorbitol: an underrecognized condition

Sodium polystyrene sulfonate (Kayexalate) in sorbitol given as an enema or orally to treat hyperkalemia has been reported to induce intestinal necrosis in uremic patients. We studied the clinical and pathologic features of 15 patients in whom Kayexalate crystals were observed in specimens from gastrointestinal surgical resections (n = 9) or endoscopic biopsies (n = 7). Oral or nasogastric tube administration of Kayexalate in sorbitol was documented in 10 patients. Among 12 patients with colorectal specimens, necrosis was observed in nine patients (75%), represented by seven of eight surgical resection specimens and three of five endoscopic biopsy specimens. No other cause of colorectal necrosis apart from Kayexalate in sorbitol was apparent in seven patients, and four also had necrosis of the small intestine. Four patients with colonic necrosis in their initial resection specimen developed progressive necrosis of the small intestine or rectum, and five patients (56%) had fatal outcome within 1 day to 6 weeks. Kayexalate crystals were observed in upper gastrointestinal tract specimens from four patients, including one with hemorrhagic gastritis. Our findings provide additional evidence that Kayexalate in sorbitol administered orally or by nasogastric tube can produce necrosis in the gastrointestinal tract.