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Nephrol Dial Transplant (2012) 27: 752–757 doi: 10.1093/ndt/gfr189 Advance Access publication 26 May 2011 Intermediate bioelectrolyte changes after phospho-soda or polyethylene glycol precolonoscopic laxatives in a population undergoing health examinations Wei-Chih Kan1,2,*, Hsien-Yi Wang1,3,*, Chih-Chiang Chien1,4, Che-Kim Tan5,6, Ching-Yih Lin6,7 and Shih-Bin Su8,9 1 Division of Nephrology, Department of Medicine, Chi-Mei Medical Center, Tainan, Taiwan, 2Department of Medical Laboratory Science and Biotechnology, Chung Hwa University of Medical Technology, Tainan, Taiwan, 3Department of Sport Management, College of Leisure and Recreation Management, Chia Nan University of Pharmacy and Science, Tainan, Taiwan, 4Department of Food Nutrition, Chung Hwa University of Medical Technology, Tainan, Taiwan, 5Department of Intensive Care Medicine, Chi-Mei Medical Center, Tainan, Taiwan, 6Institute of Medical Research, Chang Jung Christian University, Tainan, Taiwan, 7Department of Gastroenterology, Chi-Mei Medical Center, Tainan, Taiwan, 8Department of Family Medicine, Chi-Mei Medical Center, Taiwan and 9 Institute of Biomedical Engineering, Southern Taiwan University, Taiwan Correspondence and offprint requests to: Shih-Bin Su; E-mail: [email protected] *These authors have equally contributed to this work. Abstract Background. Colonoscopy is a common procedure for diagnosing and screening colon cancer and other bowelrelated diseases. Many studies have pointed out that using phospho-soda as a bowel preparation can cause obvious electrolyte abnormalities or acute kidney injury. Nonetheless, there are few studies related to its prevalence and risk factors in the population undergoing health examinations. Our aim was to compare the biochemical and electrolyte changes after using two commonly used bowel preparation regimens in this population. Methods. In this retrospective study, we collected data about participants who, before a screening colonoscopy, used oral phospho-soda laxatives in 2006, and those who used polyethylene glycol-based laxatives in 2005. Several serum biochemical and electrolyte profiles were compared between the two groups. Additional risk factors of hyperphosphatemia, a well-known side effect of phospho-soda, were also derived. Results. We enrolled a total of 2270 participants (1321 in 2005; 1449 in 2006). The basic demographic data of the two groups were not statistically different. Nonetheless, between the two groups, some serum biochemical and electrolytic data differed significantly: in those using oral phospho-soda laxatives, we found a higher prevalence of hyperuricemia, hypocalcemia, hypokalemia, hypernatremia and hyperphosphatemia. Further analyses showed that using oral phosphosoda laxatives was a risk factor for hyperphosphatemia; conversely, being male was a protective factor. Conclusions. Oral phospho-soda laxatives indeed influence the biochemical and electrolyte profiles of persons undergoing health examinations. One should be careful when interpreting bioelectrolytic data while using phospho-soda as a bowel preparation. Keywords: colonoscopy; Fleet phospho-soda; hyperphosphatemia; hyperuricemia; hypocalcemia Introduction High-phosphate-containing enemas and laxatives (such as Fleet phospho-soda, Visicol and OsmoPrep) are widely used as bowel preparations before colonoscopy due to their effectiveness and patient compliance [1]. However, recently, there have been many reports of severe complications, such as acute renal failure [2–6] and tetany due to hypocalcemia [7–9]. For example, in a 71-year-old woman who developed electrolyte abnormalities and acute kidney injury (AKI), a renal biopsy revealed different grades of calcium–phosphate deposition in the distal tubules and interstitial tissue [10]. This case led to a new term: acute phosphate nephropathy (APhN). A study [11] of 21 cases found that the patients shared various degrees of renal and electrolyte abnormalities after taking phospho-soda laxatives. The risk factors included being white, female, elderly and dehydrated, as well as taking medications that affect the glomerular filtration rate (GFR), such as diuretics, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and nonsteroidal anti-inflammatory drugs. As many adverse events had been reported [12–18], the The Author 2011. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please e-mail: [email protected] Bioelectrolyte changes after laxatives American Food and Drug Administration also disclosed reports about the side effects of several phospho-soda laxatives [19]. AKI caused by phospho-soda laxatives is rare but severe, and it can lead to irreversible renal function declines that require long-term dialysis. Drinking >45 mL of phospho-soda laxatives may cause electrolyte disturbances, such as shifts in serum levels of calcium, phosphate, sodium and potassium, but rarely apparent adverse events [20, 21]. Research on the adverse effects of phospho-soda is usually done on patients. There are, however, few published reports of bioelectrolyte and renal function changes in relatively healthy populations after they have used phospho-soda laxatives. One large-scale survey of relatively healthy individuals who took oral phospho-soda laxatives before a screening colonoscopy [22] focused on the changes in renal function 12–24 months later. Therefore, because of our desire to prevent possible adverse events or misinterpretation of laboratory data on health examinations, we conducted a study on a relatively healthy population to assess the prevalence and severity of various bioelectrolyte and renal function changes after the use of phospho-soda laxatives and to identify the characteristics of individuals at high risk for bioelectrolyte abnormalities. Materials and methods In 2006, the Healthcare Center of Chi-Mei Medical Center in Taiwan introduced a phospho-soda product (Fleet phospho-soda; CB Fleet Company, Inc., Lynchburg, VA) as a substitute for polyethylene glycol (PEG) laxatives (Klean-prep; Helsinn Birex Pharmaceuticals Ltd, Dublin, Ireland, UK) for bowel preparation before a health examination. Most of the study participants were employed at companies that offered annual or biannual medical screening. We collected data from participants who took oral phospho-soda laxatives for bowel preparation for a screening colonoscopy and had complete bioelectrolyte analyses in 2006. A group of participants who used PEG laxatives in 2005 served as the control group. The participants were all relatively healthy and had no known conflicts with the contraindications of the currently approved phospho-soda bowel preparations: age < 18 years, history of overt renal function impairment or on dialysis, congestive heart failure, ascites, bowel obstruction, toxic colitis or megacolon or other acute gastrointestinal problems, such as acute gastrointestinal bleeding or severe inflammatory bowel disease [23]. Participants who met the above criteria or had incomplete biochemical data were excluded from the analysis. This study was approval by the Institutional Review Board of Chi-Mei Medical Center and complied with patient confidentiality. Bowel preparation procedure All participants in the phospho-soda group drank 45 mL of phospho-soda (each 5 mL contained 2.4 g of monobasic sodium phosphate, 0.9 g of dibasic sodium phosphate and 556 meq of sodium) at 8 am and 8 pm 1 day prior to colonoscopy. The patients were asked to take each dose with 360 mL of water, along with 240–480 mL of water per hour thereafter to prevent dehydration. Participants in the PEG group drank the solution with one sachet of Klean-Prep in 1 L of cold water, at the rate of 250 mL every 10–15 min, till the bowel content was clear or up to four sachets, since 6 pm 1 day prior to colonoscopy. In these two groups, clear liquid diet regimens were kept for one whole day before colonoscopy, and blood sampling was taken at 8 am on the examination day (~24 h after ingesting the first dose of phospho-soda; 14 h after Klean-Prep). Those who participated in the study completed a basic physical examination, urinalysis, complete blood count and serum bioelectrolyte analyses. The estimated GFR (eGFR) was calculated according to the Modification of Diet in Renal Disease study formula [24, 25]. Demographic and clinical data were collected from the medical records. 753 Statistical analysis We entered the data into a Microsoft Excel 2007 spreadsheet and imported it to SPSS 17.0 (SPSS Inc., Chicago, IL) for statistical analysis. Descriptive analyses were done on various serum biochemical and electrolyte abnormalities. For differences between the two groups, ordinal demographic data were evaluated using the v2 test or Fisher’s exact test, and continuous data were evaluated using Student’s t-test. Furthermore, logistic regression analyses were used to estimate the possible risk factors of bioelectrolyte abnormalities. All tests were performed at a two-tailed significance level of 0.05. Results Excluding patients with incomplete data, data from the records of 2770 participants were studied. Of the 1321 who underwent health examinations in 2005 [Group 2005: 769 men (58.2%); 927 between 40 and 65 years old (70.2%)], 1253 underwent a colonoscopy (94.9%). In 2006, 1449 patients underwent health examinations [Group 2006: 894 men (61.7%); 1020 between 40 and 65 years old (70.4%)] and 1394 (96.2%) underwent a colonoscopy. The two groups did not significantly differ in terms of basic demographic data (Table 1). Among those who did not have a colonoscopy, renal function indicators and electrolyte levels did not differ between the 2005 and 2006 groups (Table 2). In contrast, among those who did have a colonoscopy, all the variables analyzed, except for serum creatinine, eGFR and urinary parameters, differed significantly between the 2005 and 2006 groups. The prevalence of patients with serum uric acid levels >9.0 mg/dL differed remarkably between those given phospho-soda laxatives in 2006 (phospho-soda group) and those given PEG laxatives in 2005 (PEG group) (9.9 versus 6.2%, P ¼ 0.001). The phospho-soda group also had a higher prevalence of hypocalcemia (<8.8 mg%) (12.9 versus 4.9%, P < 0.001), hypernatremia (145–152 mEq/L) (12.3 versus 4.2%, P < 0.001), hypokalemia (<3.0 mEq/L) (1.1 versus 0.1%, P < 0.001) and hyperphosphatemia (>4.7 mg%) (30.1 versus 4.5%, P < 0.001); they also had a high calcium–phosphate product (Ca 3 P > 55 mg2/dL2) (4.2 versus 0.3%, P < 0.001) (Table 2). Univariate regression showed that using phospho-soda laxatives was a risk factor for developing hyperphosphatemia [odds ratio (OR) ¼ 8.95, 95% confidence interval (CI): 6.72–11.92] as was a low body mass index (BMI). Being male was a protective factor (OR ¼ 0.53, 95% CI: 0.44–0.65). Multivariate regression showed that using phospho-soda laxatives was an independent risk factor for hyperphosphatemia (OR ¼ 9.49, 95% CI: 7.06–12.74), while being male was an independent protective factor (OR ¼ 0.49, 95% CI: 0.39–0.62) (Table 3). The differences in age between those with and without hyperphosphatemia were not significant. Discussion We found that phospho-soda and PEG laxatives led to no obvious renal function impairments, but they did cause different serum electrolyte changes, which implies that 754 W.-C. Kan et al. a Table 1. Demographic data of the two study groups (n ¼ 2770) Group 2005b Group 2006c All P (n ¼ 1321) Laxative before a colonoscopy No 68 Yes 1253 Gender Female 552 Male 769 Age <40 265 40–65 927 >65 129 BMI <18.5 47 18.5–24.0 664 24.0–27.0 389 >27 220 % (n ¼ 1449) % (n ¼ 2770) % 5.1% 94.9% 55 1394 3.8% 96.2% 123 2647 4.4% 95.6% 41.8% 58.2% 555 894 38.3% 61.7% 1107 1663 40.0% 60.0% 20.0% 70.2% 9.8% 302 1020 127 20.8% 70.4% 8.8% 567 1947 256 20.5% 70.3% 9.2% 3.6% 50.3% 29.5% 16.6% 75 735 408 231 5.2% 50.7% 28.2% 15.9% 122 1399 797 451 4.4% 50.5% 28.8% 16.3% 0.084 0.061 0.619 0.191 a P: v2 test. Group 2005 used a PEG-based laxative, only if they underwent a colonoscopy. c Group 2006 used a phospho-soda laxative, only if they underwent a colonoscopy. b the ‘electrolyte loading’ of phospho-soda laxatives exceeded the rate of renal excretion even after 1 day in a relatively healthy population. It is noteworthy that as many as 30.1% of the participants had hyperphosphatemia. Previous studies have shown that hyperphosphatemia may occur in healthy individuals, but that it is often transient and asymptomatic. In one study [26] of seven healthy individuals who used the standard oral phospho-soda regimen, peak serum phosphate levels were reached 6 h after they had ingested the first dose, while mild hyperphosphatemia remained after 24 h. A study [27] of 24 healthy adult volunteers showed that serum phosphate levels peaked at 14 h and then returned to normal limits within 24 h. The recommended dietary allowance for phosphorus in adults is ~0.7– 1.25 g/day; therefore, a 90-mL dose of phospho-soda has 43.2 g of monobasic sodium phosphate and 16.2 g of dibasic sodium phosphate, equivalent to 11.52 g of elemental phosphate, which gives the kidney a large phosphate burden. In addition, when a person is dehydrated, the proximal tubules not only increase the reuptake of water but also of phosphate, which reduces the excretion of phosphate. Therefore, current known risk factors for developing hyperphosphatemia include age [28], dehydration [29], drugs that affect the GFR [30], diabetes mellitus [31], and chronic kidney disease [32]. Additionally, a marked increase of phosphate causes calcium deposition within blood and tissues, causing distal renal tubule obstruction (i.e. APhN) or obstruction of small arteries [33], which may be evaluated by the calcium–phosphate product (Ca 3 P). In current practical guidelines, this value is suggested to be <55 mg2/dL2 [34]; otherwise, the risk of coronary arterial and ectopic calcification (calciphylaxis) increases significantly [11, 35–37]. Therefore, we use the product of 55 as a cutoff point of calcium–phosphate deposition. In our study, the values of Ca 3 P among the participants using phosphosoda were also significantly higher than for the PEG group, even 24 h after use. Although the duration of a high Ca 3 P product is uncertain, it may cause more obvious calcium–phosphate deposit in the distal renal tubule, and this can lead to APhN. Moreover, phospho-soda contains large amounts of sodium and so serum sodium rises [27]. If patients have edema or heart failure, symptoms of fluid overload can worsen; our data showed that 12.3% of participants developed hypernatremia. Furthermore, the risks of hypocalcemia and hypokalemia also increased with phospho-soda use. Our results for phospho-soda agreed with those of other studies [38]. Interestingly, we found that, regardless of univariate and multivariate regression analyses, being male was a protective factor against the development of hyperphosphatemia (OR ¼ 0.49, 95% CI, 0.39–0.62). Another study [10] also found that women were predominant among patients with APhN. One possible explanation is that women have lower body weight and BMI than men but took the same phospho-soda dose [39]. However, the eGFR value was higher in women than in men in our study population (Table 4), and a higher eGFR reflects a higher capacity for phosphate excretion. Therefore, dosage alone does not completely explain this phenomenon. A previous study [40] offers a possible explanation: in a rabbit model, female hormones, such as estradiol-17, estrone and estriol, stimulated the reuptake of phosphate in the proximal tubule. The authors concluded that at biological levels, female hormones stimulated proximal tubular reuptake of phosphate via an estrogen receptor-mediated pathway. Perhaps this explains, in part, why men excrete more phosphate, thus reducing the elevation of serum phosphate, and have a lower risk of APhN. Our study has some limitations. (i) The participants were fee-paying patients undergoing health examinations. Although no obvious renal function deterioration was detected after taking the phospho-soda laxatives, we had no available baseline creatinine clearance rate data; thus, ‘minor’ AKI in the participants might have been underestimated. (ii) Because it was a retrospective study, and some of the measured parameters are weak Bioelectrolyte changes after laxatives 755 a Table 2. Comparison of renal function and bio-electrolyte changes between Group 2005 and Group 2006 (n ¼ 2770) Participants who took a laxative bowel preparation before a colonoscopy (n ¼ 2647) Participants not undergoing colonoscopy and took no laxative bowel preparation (n ¼ 123) P Variable Group 2005 Group 2006 0.98 6 0.21 0.99 6 0.25 Group 2005 Serum creatinine (mg/dL) Renal function (eGFR: mL/ min/ 1.73m2) <30 30–60 >60 Uric acid (mg/dL) <7.0 7.0–9.0 >9.0 Serum calcium (mg/dL) <8.8 8.8–10.4 >10.4 Serum phosphate (mg/dL) 4.7 >4.7 Ca 3 P (mg2/dL2) 55 >55 Serum sodium (mEq/L) 125–130 130–145 145–152 Serum potassium (mEq/L) <3.0 3.0–5.0 >5.0 USG <1.005 1.005–1.030 >1.030 Urine protein Negative Trace 11 21 31 2 69 1182 0.2% 5.5% 94.3% 7 78 1309 P % 0.06b 0.356 0.5% 5.6% 93.9% % Group 2006 0.96 6 0.21 % 0.18b 0.446c 1.02 6 0.27 0 3 65 0% 4.4% 95.6% 1 4 50 1.8% 7.3% 90.9% 53 12 3 77.9% 17.6% 4.4% 33 18 4 60.0% 32.7% 7.3% 4 63 1 5.9% 92.6% 1.5% 2 51 2 3.6% 92.7% 3.6% 0.001 770 405 78 61.5% 32.3% 6.2% 780 475 138 56.0% 34.1% 9.9% <0.001 61 1185 7 4.9% 94.6% 0.6% 180 1210 4 12.9% 86.8% 0.3% 95.5% 4.5% 975 419 69.9% 30.1% 66 2 97.1% 2.9% 52 3 94.5% 5.5% 0.447c <0.001 1249 4 99.7% 0.3% 1335 59 95.8% 4.2% 1 1199 53 0.1% 95.7% 4.2% 0 1223 171 0% 87.7% 12.3% <0.001c 68 0 0 63 5 100% 0% 0% 92.6% 7.4% 54 1 98.2% 1.8% 0 52 3 0% 94.5% 5.5% 0.1% 98.7% 1.2% 16 1370 8 1.1% 98.3% 0.6% 44 841 328 3.7% 69.3% 27.0% 45 922 395 3.3% 67.7% 29.0% 903 164 96 18 12 75.7% 13.7% 8.0% 1.5% 1.0% 1036 176 101 14 13 77.3% 13.1% 7.5% 1.0% 1.0% 0.73c 1.00c <0.001 1 1237 15 0.652c 0.656c <0.001 1197 56 0.106c 0 68 0 0% 100% 0% 0 55 0 0% 100% 0% 0.417c 0.516 3 41 22 4.5% 62.2% 33.3% 1 40 14 1.8% 72.7% 25.5% 49 8 6 1 1 75.4% 12.3% 9.2% 1.5% 1.5% 44 6 5 0 0 80.0% 10.9% 9.1% 0% 0% 0.793 0.768c a USG, urine specific gravity; P, v2 test. Student’s t-test. c Fisher’s exact test. b indicators (e.g. urinary specific gravity), some findings of bioelectrolyte abnormalities in our study seemed difficult to illustrate (e.g. hyperuricemia). In conclusion, new generation high-phosphatecontaining laxative preparations offer more convenient and comfortable bowel preparation for patients undergoing a routine preventive colonoscopy. Although the bioelectrolyte changes after phospho-soda were obvious, their effects seemed transient and mostly asymptomatic in a relatively healthy population. Still, after the study, we reminded our staff to pay more attention to the pos- sibility that patients who take Fleet phospho-soda might develop hyperphosphatemia. In addition, the increased incidence of bioelectrolyte disturbance may not only cause physicians to misinterpret the biochemical and electrolyte results but could also increase the risk of calcium–phosphate deposition, especially in the distal renal tubule, and this can lead to APhN. Thus, due to the high incidence of phospho-soda-related bioelectrolyte problems, it is important to make adjustments to the bowel preparation protocol for colonoscopy, such as identifying risk factors in high-risk groups by closely 756 W.-C. Kan et al. Table 3. Predictors of hyperphosphatemia (serum P > 4.7 mg/dL) via univariate and multivariate analysesa 2. Laxative PEG Phospho-soda Gender Female Male Age <40 40–65 >65 BMI <18.5 18.5–24.0 24.0–27.0 >27 OR (95% CI)b AOR (95% CI)c 1 8.95 (6.72–11.92)* 1 9.52 (7.12–12.72)* 1 0.53 (0.44–0.65)* 1 0.49 (0.39–0.61)* 1 1.08 (0.84–1.39) 1.15 (0.78–1.69) 1 1.21 (0.92–1.60) 1.25 (0.82–1.91) 1 0.71 (0.46–1.09) 0.48 (0.30–0.75)* 0.49 (0.30–0.80)* 1 0.88 (0.55–1.41) 0.67 (0.40–1.11) 0.67 (0.39–1.14) 3. 4. 5. 6. 7. a P, phosphorus; AOR, adjusted OR. b Univariate logistical regression. c Multivariate logistical regression, with independent variables: laxative, gender, age and BMI. *P < 0.05. 8. 9. Table 4. Body weight (BW), BMI and eGFR among participants (by gender) taking phospho-soda laxativea BW (kg) BMI (kg/m2) eGFR (mL/min) a Male Female 70.07 6 10.75 24.42 6 3.21 78.20 6 12.1 55.83 6 9.07 22.70 6 3.76 82.90 6 17.2 P <0.001 <0.001 <0.001 P, Student’s t-test. 10. 11. 12. 13. monitoring electrolyte and renal function profiles, giving adequate fluid replacement and withholding drugs that affect glomerular filtration during laxative use. Because of our study findings, we had to pay much attention to these potential hyperphosphatemic participants after they had used Fleet phospho-soda, for fear that they would probably develop APhN in the following weeks. Additional monitoring of bioelectrolytic data should be considered for women. 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Rostom A, Jolicoeur E, Dubé C et al. A randomized prospective trial comparing different regimens of oral sodium phosphate and polyethylene glycol-based lavage solution in the preparation of patients for colonoscopy. Gastrointest Endosc 2006; 64: 544–552 Received for publication: 23.11.10; Accepted in revised form: 17.3.11