Pathogenesis of nephrocalcinosis after sodium phosphate catharsis to prepare for colonoscopy: Intestinal phosphate absorption and its effect on urine mineral and electrolyte excretion

Kidney injury after sodium phosphate solution beyond the acute renal failure

BACKGROUND AND OBJECTIVES

Screening colonoscopy with polipectomy reduces colonorectal cancer incidence and mortality. An adequate bowel cleansing is one of the keys to achieving best results with this technique. Oral sodium phosphate solution (OSP) had a widespread use in the 90s decade. Its efficacy was similar to polyethylene glycol (PEG) solution, but with less cost and convenient administration. Series of patients with acute renal failure due to OSP use have been reported. However, large cohorts of patients found no difference in the incidence of renal damage between these two solutions.

METHODS

From 2006 to 2009 we identified twelve cases of phosphate nephropathy after colonoscopy prepared with OSP. All patients were followed up to six months. All patients had received just a single dose.

RESULTS

We analyzed 12 cases with phosphate nephropathy; three patients debuted with AKI and nine patients had chronic renal injury. Four cases were confirmed with renal biopsy. One patient with AKI needed hemodialysis at diagnosis without subsequent recovery. Two patients (both with chronic damage) fully recovered their previous renal function. The remaining patients (nine) had an average loss of estimated glomerular filtration rate of 24ml/min/1.73m(2).

CONCLUSIONS

The use of OSP can lead to both acute and chronic renal damage. However, chronic injury was the most common pattern. Both forms of presentation imply a significant and irreversible loss of renal function. Further studies analyzing renal damage secondary to bowel cleaning should consider these two different patterns of injury.

Evaluation of intestinal phosphate binding to improve the safety profile of oral sodium phosphate bowel cleansing

Prior to colonoscopy, bowel cleansing is performed for which frequently oral sodium phosphate (OSP) is used. OSP results in significant hyperphosphatemia and cases of acute kidney injury (AKI) referred to as acute phosphate nephropathy (APN; characterized by nephrocalcinosis) are reported after OSP use, which led to a US-FDA warning. To improve the safety profile of OSP, it was evaluated whether the side-effects of OSP could be prevented with intestinal phosphate binders. Hereto a Wistar rat model of APN was developed. OSP administration (2 times 1.2 g phosphate by gavage) with a 12h time interval induced bowel cleansing (severe diarrhea) and significant hyperphosphatemia (21.79 ± 5.07 mg/dl 6h after the second OSP dose versus 8.44 ± 0.97 mg/dl at baseline). Concomitantly, serum PTH levels increased fivefold and FGF-23 levels showed a threefold increase, while serum calcium levels significantly decreased from 11.29 ± 0.53 mg/dl at baseline to 8.68 ± 0.79 mg/dl after OSP. OSP administration induced weaker NaPi-2a staining along the apical proximal tubular membrane. APN was induced: serum creatinine increased (1.5 times baseline) and nephrocalcinosis developed (increased renal calcium and phosphate content and calcium phosphate deposits on Von Kossa stained kidney sections). Intestinal phosphate binding (lanthanum carbonate or aluminum hydroxide) was not able to attenuate the OSP induced side-effects. In conclusion, a clinically relevant rat model of APN was developed. Animals showed increased serum phosphate levels similar to those reported in humans and developed APN. No evidence was found for an improved safety profile of OSP by using intestinal phosphate binders.

Sodium phosphate does not increase risk for acute kidney injury after routine colonoscopy, compared with polyethylene glycol

BACKGROUND & AIMS

Oral sodium phosphate (OSP) is a common bowel purgative administered before colonoscopy; the Food and Drug Administration has warned against its use because of concerns about acute kidney injury (AKI) from the absorbed phosphate and dystrophic calcification. However, it is not clear if OSP is associated with AKI in the general population or in high-risk subgroups undergoing colonoscopy. We estimated the risk of AKI among patients undergoing a screening colonoscopy using OSP vs polyethylene glycol (PEG) for bowel cleansing in a large, US-based claims database.

METHODS

We used an insurance database to identify a cohort of patients ages 50 to 75 years who underwent screening colonoscopies as outpatients from January 2000 through November 2008 (before the Food and Drug Administration warning), receiving OSP (n = 121,266) or PEG (n = 429,430) within 30 days beforehand, without prior use of either drug. We collected data from patients for 6 months afterward to identify those who developed AKI or renal failure, or received dialysis. Adjusted and propensity score-matched hazard ratios (HR) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models. We investigated the effects in subgroups with higher AKI risk (patients with chronic kidney disease, kidney stones, hypertension, or diabetes, or using antihypertensive or nonsteroidal anti-inflammatory drugs).

RESULTS

AKI occurred in 0.2% of OSP users and in 0.3% of PEG users (adjusted HR, 0.86; 95% CI, 0.75-0.99). OSP users matched well with PEG users, producing similar estimates (HR, 0.85; 95% CI, 0.72-1.01). We did not observe a consistent increase in the risk of AKI or other outcomes in any subgroups analyzed.

CONCLUSIONS

In a large database analysis, we did not associate administration of OSP before colonoscopy with increased risk of postprocedure AKI, even in high-risk clinical subgroups.

Colonoscopy preparation-induced disorders in renal function and electrolytes

Colonoscopy and flexible sigmoidoscopy are commonly used mainly for colon cancer screening and detection, but also in several other situations such as inflammatory bowel disease (for diagnosis and follow up) and gastrointestinal hemorrhage. Bowel cleansing preparations mainly include polyethylene glycol and oral sodium phosphate solutions, with the later being most frequently used due to better toleration from patients. Despite their favourable safety profile these agents have been associated with renal function deterioration and electrolyte disorders, some of which were serious or even fatal. The present paper discusses the complications associated with colonoscopy preparation agents.

Advances in bowel preparations: new formulation and clinical results

Adequate cleansing is essential for a thorough and accurate examination of the bowel during colonoscopy. Suboptimal preparation can lead to missed diagnoses, increased costs, and safety issues. Favorable bowel preparations are efficacious, safe, and cause as little patient discomfort as possible by limiting fluid volume, intolerance, and inconvenience. Split-dose (2-day) regimens address these concerns and are associated with better cleansing and higher patient satisfaction than with single-dose regimens. Nurses can play a key role in communicating the benefits of various bowel preparation options, including split dosing, to patients.A low-volume oral sulfate solution given as a split-dose regimen has been tested in randomized clinical trials and found to provide similar bowel cleaning to split-dose polyethylene glycol with electrolytes and ascorbic acid (PEG-EA). Superior cleaning was found when compared with single-dose polyethylene glycol with electrolytes (PEG-ELS), particularly in the cecum and ascending colon. With the exception of clinically insignificant changes in electrolytes, tolerability and safety were similar between patients taking oral sulfate solution and patients taking PEG-EA or PEG-ELS. Oral sulfate solution is a safe and effective low-volume bowel preparation for colonoscopy.

Renal risks of sodium phosphate tablets for colonoscopy preparation: a review of adverse drug reactions reported to the US Food and Drug Administration

AIM

Sodium-phosphate-containing colonoscopy preparations cause renal failure by the development of calcium phosphate nephropathy. Although Fleet's Phospho-Soda has been removed from the US market, sodium phosphate tablets sold as OsmoPrep and Visicol remain available. Our aim was to analyse renal risks of the sodium phosphate tablets.

METHOD

We conducted a retrospective study using the US Food and Drug Administration Adverse Event Reporting System, a voluntary reporting system available for public access. Renal adverse events were identified using search terms including renal impairment, increased blood urea nitrogen, increased creatinine, renal failure, acute renal failure, chronic renal failure, acute phosphate nephropathy, nephrocalcinosis, renal tubular necrosis, haemodialysis, nephropathy toxic, dialysis, peritoneal dialysis, renal injury, renal tubular disorder, decreased glomerular filtration rate and decreased creatinine clearance. Patient age, gender and body weight were compared with data for the general population in the National Health and Nutrition Examination Survey (NHANES).

RESULTS

In total 2,097,223 files were extracted from the US Food and Drug Administration website for 2004-2008 and the first 9 months of 2009. Of these, 178 patients on tablet preparations (71% women) were identified, with increasing numbers of renal adverse drug reactions reported from tablet preparations each year. The mean weight for women with renal complications from tablet preparations was 68.57 ± 1.78 kg, significantly lower than the national average weight of 74 ± 0.5 kg for the same age group (P = 0.003) in NHANES.

CONCLUSION

Renal adverse drug reactions from sodium phosphate tablets are more common in women with a mean body weight lower than the national average weight.

Severe hypocalcaemia and hyperphosphataemia caused by oral sodium phosphate fleet solution in a haemodialysis patient after parathyroidectomy

We report a case with severe electrolyte disturbance after the use of oral sodium phosphate solution (OSPS). A 69-year-old patient on haemodialysis received 45 mL of OSPS for bowel preparation. He had symptomatic hypocalcaemia with a serum calcium level of 0.95 mmol/L and serum phosphate level of 4.73 mmol/L. He was treated with haemodialysis and intravenous calcium supplementation. This patient had total parathyroidectomy recently leading to the absence of parathyroid hormone response. OSPS has been reported to cause life-threatening electrolyte disturbance especially in patients with renal failure. We suggest the use of safer alternatives for bowel preparations in renal failure patients.

Lower body weight and female gender: Hyperphosphatemia risk factors after sodium phosphate preparations

Casais et al have reported an inverse correlation between serum phosphate and body weight after administration of sodium phosphate at a dose of 60 g. Our group has already described the relationship between body weight and hyperphosphatemia with these preparations, although our study was not quoted by Casais. We performed a pharmacokinetic study involving 13 volunteers who were divided into two groups on the basis of body weight: group I consisting of seven women with a median weight of 60 kg and group IIconsisting of five men and one woman with a median weight of 119.2 kg. Group I developed higher peak phosphate levels and maintained these levels above the subjects in Group II for a prolonged time period despite adequate hydration being ensured with frequent monitoring of weight, fluid intake and total body weight. Our study demonstrated that adequate hydration does not protect against the secondary effects of hyperphosphatemia. In the study by Casais et al, 66% of the study subjects were women, the correlation between serum phosphate and gender in their data also appears to be important. Women are at higher risk of acute phosphate nephropathy due to a diminished volume of distribution of the high dose of ingested phosphate. Decreased volume of distribution in women is due to diminished body weight. This is further compounded by decreased creatinine clearance in females.

Hyperphosphatemia after sodium phosphate laxatives in low risk patients: prospective study

AIM

To establish the frequency of hyperphosphatemia following the administration of sodium phosphate laxatives in low-risk patients.

METHODS

One hundred consecutive ASA I-II individuals aged 35-74 years, who were undergoing colonic cleansing with oral sodium phosphate (OSP) before colonoscopy were recruited for this prospective study.

EXCLUSION CRITERIA

congestive heart failure, chronic kidney disease, diabetes, liver cirrhosis, intestinal obstruction, decreased bowel motility, increased bowel permeability, and hyperparathyroidism. The day before colonoscopy, all the participants entered a 24-h period of diet that consisted of 4 L of clear fluids with sugar or honey and 90 mL (60 g) of OSP in two 45-mL doses, 5 h apart. Serum phosphate was measured before and after the administration of the laxative.

RESULTS

The main demographic data (mean +/- SD) were: age, 58.9 +/- 8.4 years; height, 163.8 +/- 8.6 cm; weight, 71 +/- 13 kg; body mass index, 26 +/- 4; women, 66%. Serum phosphate increased from 3.74 +/- 0.56 to 5.58 +/- 1.1 mg/dL, which surpassed the normal value (2.5-4.5 mg/dL) in 87% of the patients. The highest serum phosphate was 9.6 mg/dL. Urea and creatinine remained within normal limits. Post-treatment OSP serum phosphate concentration correlated inversely with glomerular filtration rate (P < 0.007, R(2) = 0.0755), total body water (P < 0.001, R(2) = 0.156) and weight (P < 0.013, R(2) = 0.0635).

CONCLUSION

In low-risk, well-hydrated patients, the standard dose of OSP-laxative-induced hyperphosphatemia is related to body weight.

Increased serum phosphate levels and calcium fluxes are seen in smaller individuals after a single dose of sodium phosphate colon cleansing solution: a pharmacokinetic analysis

BACKGROUND

Sodium phosphate containing colonoscopy preparations may cause electrolyte disturbances and calcium-phosphate nephropathy. Decreased body weight is an unexplored risk factor for complications with sodium phosphate ingestion.

AIM

To perform a pharmacokinetic analysis of a single dose of Fleet Phospho-Soda in smaller and larger individuals.

METHODS

Seven subjects weighing <55 kg (Group I) and six weighing >100 kg (Group II) consumed 45 mL Fleet Phospho-Soda. Serum electrolytes were measured. Hydration was closely maintained by monitoring weight, fluid intake and total body water.

RESULTS

Marked increases in serum phosphate were seen in Group I compared to Group II. For example, mean serum phosphate at 120 min was 7.8 +/- 0.5 mg/dL in Group I and 5.1 +/- 0.8 mg/dL in Group II (P < 0.001). Normalized area under the phosphate vs. time curve for Group I was 1120 +/- 190 mg/dL*min and 685 +/- 136 mg/dL*min for Group II (P < 0.001). Twelve-hour urine calcium was lower in Group I (16.4 +/- 7.6 mg) than in Group II (39.2 +/- 7.8 mg, P < 0.001).

CONCLUSIONS

Increased serum phosphate occurs in smaller individuals after ingestion of sodium phosphate preparations, even with strict attention to fluid intake. Smaller body weight poses a potential risk for calcium-phosphate nephropathy.

Intestinal and renal effects of low-volume phosphate and sulfate cathartic solutions designed for cleansing the colon: pathophysiological studies in five normal subjects

OBJECTIVES

Ingestion of a concentrated low-volume phosphate solution produces copious diarrhea, which cleanses the colon, but it occasionally causes renal failure due to calcium phosphate precipitation in renal tubules. We hypothesized that a concentrated low-volume sulfate solution would be an equally effective cathartic, and that urine produced after sulfate would have less tendency to precipitate calcium salts than urine produced after phosphate.

METHODS

Hydrated subjects ingested 75 ml of phosphosoda or an equimolar dose of sulfate salts in a small volume of solution. Four liters of PEG (polyethylene glycol) lavage solution was the control. All solutions were administered in split doses, 10 h apart. Propensity of urine to precipitate at pH 6.4 (the pH of renal tubular fluid) was assessed by determining the minimal calcium concentration that caused precipitation.

RESULTS

Average diarrheal stool weight was 2,004 g after phosphate, 2,854 g after sulfate, and 3,021 g after PEG (P<0.001). Average calcium concentration (in mg/dl) required to induce urine precipitation at pH 6.4 was 43 after PEG, 10 after PO(4), and 187 after SO(4) (P=0.009).

CONCLUSIONS

(i) In equimolar doses, sulfate produced 42% more diarrheal stool weight than phosphate. (ii) Phosphate increased the propensity for calcium salt precipitation in urine at pH 6.4, whereas sulfate did not. (iii) These results suggest that a hypertonic low-volume sulfate solution would be an effective cathartic for colon cleansing and that sulfate-induced catharsis would be less likely than phosphate catharsis to produce calcium salt deposition in renal tubules.

Acute phosphate nephropathy-an emerging threat

BACKGROUND

Acute phosphate nephropathy (APN) is a clinicopathological entity causing renal failure, after ingestion of oral sodium phosphate solution (OSPS). Approximately 25 cases have been described, but OSPS is still widely used. This study reports a further 5 cases and discusses the ever-growing significance of APN.

METHODS

Five cases of APN were included, 3 retrospectively whereas 2 were diagnosed prospectively. In all, use of OSPS was established, and other causes of nephrocalcinosis were excluded.

RESULTS

Average age was 67.4 +/- 7.0 years, with a female preponderance (4:1). All patients had hypertension. Baseline serum creatinine: 0.7 to 1.2 mg/dL (creatinine clearance: 52 to 77 mL/min). Time from colonoscopy to presentation was 56 +/- 36 days. Serum creatinine levels at presentation: 1.4 to 3.6 mg/dL. Time from colonoscopy to renal biopsy was 123 +/- 88 days. Urinalysis showed minimal proteinuria, leucocyturia, and hematuria. One patient had renal glucosuria. All patients were anemic (hemoglobin 8.8-11.4 gr/dL). Serum calcium and phosphate were normal. One required hemodialysis. Mean follow-up was 36 +/- 17 months. Serum creatinine levels at end of follow-up were 1.3 to 3.1 mg/dL. Renal function did not recover completely in any patient. Four required long-term erythropoietin treatment. The prominent histopathological findings were calcium-phosphate tubular depositions (100%), interstitial fibrosis (80%), hypertensive changes (80%), and acute tubular degenerative and regenerative changes (60%).

CONCLUSIONS

APN is a serious, irreversible renal complication of OSPS. It is probably under-recognized. Risk factors include female gender, older age, hypertension, and renal failure, although it may occur with preexisting normal renal function.

Is bowel preparation before colonoscopy a risky business for the kidney?

Acute phosphate nephropathy after bowel preparation with oral sodium phosphate (OSP) for colonoscopy has emerged as an important clinical entity. In 2004, five cases of nephrocalcinosis and irreversible renal failure after bowel preparation with OSP were reported. More recently, several retrospective studies have shown that the incidence of acute kidney injury after OSP use is in the range of 1-4%, similar to the incidence of contrast nephropathy in the general population. The degree of renal failure is not generally as severe as in the first reported cases, but irreversible damage can still occur. Millions of people worldwide undergo screening colonoscopies for colon and rectal cancer after the age of 50, so careful patient selection and monitoring for possible complications is essential when OSP is used. In addition to educating patients about the possibility of renal damage, physicians should routinely watch for considerable weight loss during bowel preparation and correct the fluid deficit as needed. Carrying out a renal function panel, which includes serum phosphorus level, is prudent after colonoscopy. Alternative bowel cleansing agents are needed because calcium phosphate precipitation is inevitable after OSP use even in the normal kidney.

Adverse renal and metabolic effects associated with oral sodium phosphate bowel preparation

Colorectal cancer can be prevented by the removal of adenomatous polyps during screening colonoscopy, but adequate bowel preparation is required. Oral sodium phosphate (OSP), an effective bowel purgative, is available over the counter and requires a substantially lower volume than polyethylene glycol-based preparative agents. Accumulating reports implicate OSP in electrolyte disturbances as well as acute kidney injury (AKI) in a syndrome termed phosphate nephropathy (a form of nephrocalcinosis). Despite published case reports and case series, the actual incidence, risk factors, and natural history of phosphate nephropathy remain largely undefined. Several recent observational studies have provided new information on these important issues while supporting a link between OSP and acute phosphate nephropathy as well as the development of chronic kidney disease in elderly patients, many of whom had a normal serum creatinine at the time of OSP ingestion. This review summarizes current knowledge about the renal complications of OSP, risk factors for its development, and the pathophysiology of acute and chronic kidney damage in nephrocalcinosis.

Drug-induced crystal nephropathy: an update

BACKGROUND

Several medications that are insoluble in human urine are known to precipitate within the renal tubules. Intratubular precipitation of either exogenously administered medications or endogenous crystals (induced by certain drugs) can promote chronic and acute kidney injury, termed crystal nephropathy. Clinical settings that enhance the risk of drug or endogenous crystal precipitation within the kidney tubules include true or effective intravascular volume depletion, underlying kidney disease, and certain metabolic disturbances that promote changes in urinary pH favoring crystal precipitation.

OBJECTIVE

Identify and review previously described and recently recognized medications that cause crystal nephropathy.

METHOD

A literature review was performed, using PubMed, Ovid, and Google Scholar, focusing on drugs (sulfadiazine, acyclovir, indinavir, triamterene, methotrexate (MTX), orlistat, oral sodium phosphate preparation, ciprofloxacin) that cause crystal nephropathy.

RESULTS/CONCLUSION

Sulfadiazine, acyclovir, indinavir, triamterene, and MTX are known to cause crystal nephropathy. Recently, several medications, including orlistat, ciprofloxacin, and oral sodium phosphate solution, along with underlying risk factors have been described as causing crystal nephropathy.

The renal safety of bowel preparations for colonoscopy: a comparative study of oral sodium phosphate solution and polyethylene glycol

BACKGROUND

Rare cases of nephrotoxicity have been reported with oral sodium phosphate solution (OSPS).

AIM

To evaluate whether OSPS is associated with changes in renal function.

METHODS

A chart review performed on 311 patients who had colonoscopy at the James J. Peters VA Medical Centre prepared with either OSPS (n = 157) or polyethylene glycol (PEG) (n = 154). Patients had a baseline serum creatinine <or=1.5 mg/dL. Effect of bowel preparation on the renal function was evaluated by measuring the absolute change in levels of serum creatinine and the proportion of patients who developed a 50% or more increase above their baseline serum creatinine value.

RESULTS

Oral sodium phosphate solution resulted in a slight increase in serum creatinine from 1.0 +/- 0.02 to 1.1 +/- 0.02 mg/dL (P = 0.07) and PEG resulted in a small decrease in serum creatinine from 1.1 +/- 0.02 to 1.0 +/- 0.03 mg/dL (P = 0.03). The absolute change in serum creatinine was slightly higher with OSPS than with PEG (0.04 +/- 0.02 vs. -0.05 +/- 0.02 mg/dL; P = 0.005). However, the proportion of patients who had a >or=50% increase above their baseline creatinine was similar (OSPS vs. PEG, 5% vs. 3%, P = 0.77).

CONCLUSIONS

Oral sodium phosphate solution was associated with a slight increase in serum creatinine, which was not clinically significant. Renal toxicity from OSPS appears to be minimal when used in patients with serum creatinine value <1.5 mg/dL.

Dosing considerations in the use of sodium phosphate bowel preparations for colonoscopy

OBJECTIVE

To review dosing considerations and other treatment recommendations to maximize the efficacy, tolerability, and safety of sodium phosphate (NaP) preparations.

DATA SOURCES

Literature was accessed through PubMed (1990-May 2007) and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION

English-language publications including clinical trials and case reports were evaluated. Recent reports assessing newer bowel preparations containing reduced doses of NaP were reviewed to evaluate efficacy, tolerability, and safety.

DATA SYNTHESIS

Among commonly administered bowel preparations for colonoscopy, NaP preparations are generally more effective and better tolerated compared with polyethylene glycol electrolyte lavage solution regimens. However, NaP preparations are contraindicated in specific patient populations, and clinicians must use effective screening mechanisms to select proper patients to receive NaP preparation for colonoscopy. Recently, cases of renal failure in patients with previously normal renal function have been reported after NaP preparation for colonoscopy, heightening concerns about the safety of these agents. Newer products contain reduced doses of NaP and may improve the safety and tolerability of NaP purgatives without compromising efficacy of colon cleansing. In addition, accumulating clinical data and/or rationale support split dosing of NaP products, wide intervals between doses, and aggressive hydration before and during bowel preparation and after the colonoscopy procedure.

CONCLUSIONS

Safe administration of NaP products requires rigorous attention to dosing considerations and other treatment recommendations, including administration of minimally effective doses of NaP, split-dosing schedules, and aggressive hydration.