Calcium acetate, an effective phosphorus binder in patients with renal failure

Phosphate binder usage in kidney failure patients

Phosphorus binders are used in patients with kidney failure because of the incomplete removal of phosphorus with dialysis and the inability to exclude phosphorus from the diet. Aluminium was the initial phosphorus binder used, but was replaced by calcium-containing binders because of the development of aluminium toxicity. Calcium-based binders have been the mainstay of therapy for many years, but recent investigations have pointed to increased rates of vascular calcification in patients taking calcium-containing binders. For this reason, alternative agents have been developed. Sevelamer (Renagel), GelTex Pharmaceuticals Inc.) is a polymer which has been found to effectively bind phosphorus. It has resulted in a decreased rate of vascular calcification compared to calcium-containing binders. Other agents under development include lanthanum carbonate and iron-complex preparations. Further research will likely concentrate on identifying binders that bind phosphate more efficiently, have minimal gastrointestinal side effects and provide other benefits to dialysis patients.

Safety of New Phosphate Binders for Chronic Renal Failure

Phosphate (Pi) retention is a common problem in patients with chronic kidney disease, particularly in those who have reached end-stage renal disease (ESRD). In addition to causing secondary hyperparathyroidism and renal osteodystrophy, recent evidence suggests that, in ESRD patients, high serum phosphorus concentration and increased calcium and phosphorous (Ca x P) product are associated with vascular and cardiac calcifications and increased mortality. Dietary phosphorus restriction and Pi removal by dialysis are not sufficient to restore Pi homeostasis. Reduction of intestinal Pi absorption with the use of Pi binders is currently the primary treatment for Pi retention in patients with ESRD. The use of large doses of calcium-containing Pi binders along with calcitriol administration may contribute to over-suppression of parathyroid hormone secretion and adynamic bone disease as well as to a high incidence of vascular calcifications. When used in patients with impaired renal function, aluminium salts were found to accumulate in bone and other tissues, resulting in osteomalacia and encephalopathy.Sevelamer, an aluminium- and calcium-free Pi binder can reduce serum phosphorus concentration and is associated with a significantly lower incidence of hypercalcaemia, while maintaining the ability to suppress parathyroid hormone production. An additional benefit of sevelamer is its ability to lower low density lipoprotein-cholesterol and total cholesterol levels. Sevelamer attenuates the progression of vascular calcifications in haemodialysis patients, which may lead to lower mortality. The use of sevelamer in non-dialysed patients might aggravate metabolic acidosis, common in these patients. Several other calcium-free Pi binders are in development. Lanthanum carbonate has shown significant promise in clinical trials in ESRD patients. Magnesium salts do not offer a significant advantage over currently available Pi binders. Their use is restricted to patients receiving dialysis since excess magnesium must be removed by dialysis. Iron-based compounds have shown variable efficacy in short-term clinical trials in small numbers of haemodialysis patients. Mixed metal hydroxyl carbonate compounds have shown efficacy in animals but have not been studied in humans. Major safety issues include absorption of the metal component with possible tissue accumulation and toxicity.

Improved Strategies for the Treatment of Renal Osteodystrophy

Renal osteodystrophy (ROD) encompasses several distinct skeletal complications resulting from the metabolic abnormalities associated with chronic kidney disease (CKD). Other manifestations of altered calcium and phosphorus homeostasis include an increased risk of cardiovascular mortality and morbidity. Hyperphosphatemia and secondary hyperparathyroidism (HPT) are associated with these adverse events, and ultimately can lead to ROD. Dietary restriction of phosphorus, use of phosphate binding agents, and vitamin D therapy have been the mainstay of therapy for HPT. Recently, several new therapeutic agents have become available for the management of HPT. The nonelemental phosphate binder, sevelamer hydrochloride (Renagel®) has provided an alternative to calcium-containing binders for the management of hyperphosphatemia. This agent also decreases calcium load and minimizes the risk of hypercalcemia and skin and soft tissue calcifications. Research in the area of vitamin D receptors has lead to the development of vitamin D analogs including paricalcitol (Zemplar®) and doxercalciferol (Hectorol®) as alternative agents for HPT. Potential benefits of these analogs include a lower risk of hypercalcemia and hyperphosphatemia compared with calcitriol, although further evaluation is warranted as these agents are used more in clinical practice. Calcimimetics are also in the pipeline as potential agents for management of HPT by inhibition of parathyroid hormone secretion. These new developments in the management of metabolic disorders of CKD provide pharmacotherapeutic alternatives to improve patient outcomes and prevent/manage ROD. The challenge is to determine appropriate guidelines for use of these agents at all stages of CKD.

Cardiovascular calcification in patients with end-stage renal disease: a century-old phenomenon

The mortality risk from cardiovascular disease is increased in patients with end-stage renal disease (ESRD). This is due to both traditional and dialysis-specific factors. Recently, a number of the dialysis-specific risk factors have been implicated in the pathogenesis of cardiovascular calcification. These include: hyperphosphatemia, high calcium-phosphate (Ca x P) product, elevated parathyroid hormone levels, duration of dialysis, and treatment with calcium-containing phosphate binders and vitamin D analogs. The recent availability of electron beam computed tomography (EBCT) has triggered increased awareness of the occurrence of cardiovascular calcification in ESRD patients. Given the development of transient hypercalcemia with calcium-containing binders, a link between calcium load from use of calcium-containing phosphate binders and development coronary calcification has been proposed. However, a causal relationship between use of these agents and cardiovascular calcification has not been established. Moreover, this phenomenon had been recognized over a century ago, long before these phosphate binders became available. Although its pathogenesis is likely to be multifactorial, available data strongly implicate elevated serum phosphorus as the primary culprit. Furthermore, the risk of calcification may be aggravated by vitamin D therapy, particularly in patients with severe secondary hyperparathyroidism. Therefore, achieving vigorous control of serum phosphorus, Ca x P product and parathyroid hormone level might decrease cardiovascular calcification and improve survival of patients on maintenance hemodialysis. Since calcium acetate is the most cost-effective phosphate binder available, we recommend that it should remain the first line treatment of hyperphosphatemia in patients with ESRD.

Hyperphosphatemia in end-stage renal disease

Hyperphosphatemia occurs universally in end-stage renal disease (ESRD) unless efforts are made to prevent positive phosphate balance. Positive phosphate balance results from the loss of renal elimination of phosphate and continued obligatory intestinal absorption of dietary phosphate. Increased efflux of phosphate from bone because of excess parathyroid hormone-mediated bone resorption can also contribute to increased serum phosphate concentrations in the setting of severe hyperparathyroidism. It is important to treat hyperphosphatemia because it contributes to the pathogenesis of hyperparathyroidism, vascular calcifications, and increased cardiovascular mortality in ESRD patients. Attaining a neutral phosphate balance, which is the key to the management of hyperphosphatemia in ESRD, is a challenge. Control of phosphorus depends on its removal during dialysis and the limitation of gastrointestinal absorption by dietary phosphate restriction and chelation of phosphate. Knowledge of the quantitative aspects of phosphate balance is useful in optimizing our use of phosphate binders, dialysis frequency, and vitamin D sterols. The development of new phosphate binders and efforts to find new ways to inhibit gastrointestinal absorption of phosphate will lead to improvements in the control of serum phosphate levels in ESRD.

Compounds in development to combat hyperphosphataemia

Hyperphosphataemia in haemodialysis patients is associated with secondary hyperparathyroidism and more importantly with an increased cardiovascular mortality in dialysed patients. Removal of phosphate during dialysis is less than net intestinal uptake. This imbalance results in a positive phosphate balance. To control serum phosphate concentration oral phosphate binders have to be taken to reduce net intestinal uptake. The use of classical phosphate binders such as calcium carbonate, calcium acetate and aluminium-containing phosphate binders is limited by their side effects. Hypercalcaemia aggravates vascular calcification and cardiovascular risk. Aluminium intoxication causes aluminium osteopathy, anaemia and encephalopathy. Therefore, the development of calcium- and aluminium free phosphate binders has become a challenge to clinical nephrology. Polyallylamine hydrochloride (sevelamer) is one of the new alternative compounds which has been shown to effectively bind phosphate in dialysis patients. A promising approach in the development of alternative phophate binders are trivalent-iron (Fe(III)) containing phosphate binders. They were not only successfully tested in experimental animals but have also been shown to reduce urinary phosphate excretion and serum phosphate concentrations in patients with preterminal failure and those on maintenance haemodialysis. This review outlines the experimental and clinical data on Fe-III based phosphate binders providing evidence that they will be as effective and safe as phosphate binders without the major side effects of classical phosphate-binding compounds.

Parathyroidectomy in patients on renal replacement therapy: an epidemiologic study

Secondary hyperparathyroidism is a frequent complication of long-term dialysis treatment, and despite recent advances in medical therapy, surgical parathyroidectomy (PTx) is necessary in a considerable number of uremic patients. A prevalence of PTx of 22% was reported in Europe in 1988 in patients on dialysis from 10 to 15 yr, but no large-scale epidemiologic study has been published since then. The aim of the study was to evaluate the prevalence, incidence, and risk factors for PTx in patients on renal replacement therapy (RRT) in Lombardy and to determine whether the incidence has changed over time. The study involved 14,180 patients included in the Lombardy Registry of Dialysis and Transplantation who received RRT for end-stage renal disease (ESRD) between 1983 and 1996. Cox-proportional hazards regression models were used to evaluate the risk factors of PTx, the explanatory covariates being age on admission to RRT, gender, underlying renal disease (nondiabetic or diabetic nephropathy), and dialysis modality (peritoneal dialysis or hemodialysis). The prevalence of PTx in the 7371 ERSD patients who were alive on December 31, 1996, was 5.5% and increased with the duration of RRT (9.2% after 10 to 15 yr, 20.8% after 16 to 20 yr). Similarly, the incidence of PTx increased from 3.3 per 1000 patient-years in patients who had been on RRT for <5 yr to 30 per 1000 patient-years in those receiving RRT for >10 yr. The Cox regression models showed that the relative risk for PTx was significantly higher in women and lower in elderly and diabetic patients. The relative risk for PTx (adjusted for gender, age, and nephropathy) was higher in the patients on peritoneal dialysis than in those on hemodialysis and decreased after transplantation. During the course of a follow-up of 7 yr, the incidence of PTx in patients who started RRT between 1990 and 1992 was no different from that observed in patients who started RRT between 1983 and 1985. In conclusion, the prevalence and incidence of PTx in patients receiving RRT in Lombardy is lower than that in Europe and Italy as a whole, as reported by the 1988 European Dialysis and Transplantation Association Registry; its frequency has not changed significantly during the past few years. The need for PTx decreases markedly after successful transplantation. The epidemiologic finding that the rate of PTx is greater in women, young patients, and individuals who do not have diabetes suggests the need for a more aggressive medical treatment of secondary hyperparathyroidism particularly in such patients.

Calcium acetate versus calcium carbonate in the control of hyperphosphatemia in hemodialysis patients

CONTEXT

Hyperphosphatemia has an important role in the development of bone and mineral abnormalities in end-stage renal disease (ESRD).

OBJECTIVE

To compare the phosphorus binding power and the hypercalcemic effect of calcium acetate and calcium carbonate in hemodialysis patients.

TYPE OF STUDY

Crossover, randomized, double-blind study.

PLACE

A private hospital dialysis center.

PARTICIPANTS

Fifty-two patients who were undergoing regular hemodialysis three times a week ([Ca++] dialysate = 3.5 mEq/L).

PROCEDURES

Half of the patients were started on 5.6 g/day of calcium acetate and, after a 2 week washout period, received 6.2 g/day of calcium carbonate. The other half followed an inverse protocol.

MAIN MEASUREMENTS

Clinical interviews were conducted 3 times a week to monitor for side effects. Determinations of serum urea, calcium, phosphorus, hematocrit, Kt/V and blood gas analysis were obtained before and after each treatment.

RESULTS

Twenty-three patients completed the study. A significant increase in calcium plasma levels was only observed after treatment with calcium carbonate [9.34 mg/dl (SD 0.91) vs. 9.91 mg/dl (SD 0.79), P < 0.01]. The drop in phosphorus levels was substantial and significant for both salts [5.64 mg/dl (SD 1.54) vs. 4.60 mg/dl (SD 1.32), P < 0.01 and 5.89 mg/dl (SD 1.71) vs. 4.56 mg/dl (SD 1.57), P < 0.01, for calcium acetate and calcium carbonate respectively]. The percentage reduction in serum phosphorus (at the end of the study) per milliequivalent of salt administered per day tended to be higher with calcium acetate but statistical significance was not found.

CONCLUSION

Calcium acetate can be a good alternative to calcium carbonate in the handling of hyperphosphatemia in ESRD patients. When calcium acetate is used, control of hyperphosphatemia can be achieved with a lower administration of calcium, perhaps with a lower risk of hypercalcemia.

Current medical management of secondary hyperparathyroidism

The treatment of secondary hyperparathyroidism (HPT) in patients with chronic renal disease has improved markedly in recent years. The skeletal pain, disabling fractures, tendon ruptures, and myriad other symptoms associated with HPT can now be avoided, and the quality of life of patients with end-stage renal disease is improved. Control of hyperphosphatemia, maintenance of normocalcemia, and appropriate dosing of vitamin D analogues can prevent HPT in many cases. Palatable, nutritious diets should be followed; serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone should be monitored; and treatment regimens should be adjusted accordingly. If prevention fails, and even if severe HPT develops, many of these patients can still be controlled medically with correction of hyperphosphatemia and high doses of intravenous calcitriol. In our experience, only a few patients require surgical parathyroidectomy (usually noncompliant patients or patients whose HPT has been poorly managed from early uremia). The essence to medical management is to correct the two most important pathogenetic factors of HPT, hyperphosphatemia, and calcitriol deficiency. We present the current approach to the management of HPT, with highlights of recent advances.

Severe hypophosphatemia. Pathophysiologic implications, clinical presentations, and treatment

We conducted this review to heighten the awareness and describe pathologic manifestations of hypophosphatemia. We present 3 cases of varied manifestations of hypophosphatemia where recognition was delayed. In certain settings, severe hypophosphatemia has significant morbidity and potential mortality. Appreciation of the pathophysiologic basis for organ dysfunction in severe hypophosphatemia should result in early recognition and treatment. We reviewed the English-language literature for reported cases and research studies dealing with pathophysiologic mechanisms subserving clinical manifestations. We observed that depletion of adenosine triphosphate (ATP) would explain most of the derangement noted in cellular functions. Phosphate plays a key role in the delivery of oxygen to the tissue. Lack of phosphate, therefore, leads to tissue hypoxia and hence disruption of cellular function. Severe hypophosphatemia becomes clinically significant when there is underlying phosphate depletion. Otherwise, short-term acute hypophosphatemia is not usually associated with any specific disorder. Chronic hypophosphatemia, on the other hand, results in hematologic, neuromuscular, and cardiovascular dysfunction, and unless corrected, the consequences can be grave. Most of the time hypophosphatemia results from renal loss of phosphate, diagnosed by a fractional secretion of phosphate > 5%. It is hard to provide precise estimates of how many patients are seen with hypophosphatemia annually at academic medical centers. This is complicated by use of chemistry panels that do not measure inorganic phosphate unless specifically ordered. This often leads to delay in correct diagnosis, and, therefore, additional delay in providing appropriate management. A high index of suspicion alone avoids the unnecessary withholding of treatment that can be life saving.

Long-term effects of sevelamer hydrochloride on the calcium x phosphate product and lipid profile of haemodialysis patients

BACKGROUND

Short-term studies have suggested that sevelamer hydrochloride, a non-aluminium- and non-calcium-containing hydrogel, is an effective phosphate binder in haemodialysis patients, and may produce favourable changes in the lipid profile.

METHODS

To determine the long-term effectiveness of sevelamer hydrochloride, we performed an open-label clinical trial in 192 adult patients with end-stage renal disease on haemodialysis. Drug-related changes in the concentrations of serum phosphorus, calcium, calcium x phosphate product, parathyroid hormone, and low- and high-density lipoprotein cholesterol concentrations were the major outcomes of interest.

RESULTS

Treatment with sevelamer was associated with a mean change in serum phosphorus of -0.71+/-0.77 mmol/l, serum calcium of 0. 08+/-0.22 mmol/l, and calcium x phosphate product of -1.46+/-1.78 mmol/l (P<0.0001 for all comparisons). There were no significant overall treatment-related changes in parathyroid hormone. Serum levels of LDL cholesterol decreased by 0.81+/-0.75 mmol/l (mean -30%, P<0.0001) and HDL cholesterol increased by a mean of 0.15+/-0.29 mmol/l (mean +18%, P<0.0001). Drug-related adverse events were infrequent and most were of mild intensity.

CONCLUSION

Sevelamer is a safe and effective phosphate binder that leads to significant improvements in the calcium x phosphate product and lipid profile of haemodialysis patients.

Phosphate-binding capacity of ferrihydrite versus calcium acetate in rats

Calcium salts, such as calcium carbonate and calcium acetate, are the principal compounds used as phosphate binders in patients with chronic renal failure. The dose required is three to six times the normal requirement for calcium. Use of these large doses of calcium salts in the diet can result in hypercalcemia. Other compounds have been investigated as phosphate binders with varying degrees of success. Synthetic ferrihydrite (5Fe(2)O(3).9H(2)O) has a high adsorptive capacity for phosphate and may be an effective phosphate binder. The phosphate-binding capacity of ferrihydrite was compared with that of calcium acetate in 250-g male Sprague Dawley rats. After an overnight fast, rats (n = 5 per group) were gavaged with an American Institute of Nutrition (AIN) 76 formula containing one third the daily phosphorus intake labeled with phosphorus-32 ((32)P). Either two levels of calcium acetate, representing three (1/2X) or six (1X) times the usual calcium intake for one third of the day, or equivalent amounts of ferrihydrite were added to the diet. An additional group received two times (2X) the larger dose, and a sixth control group received no binder in the diet. Phosphorus absorption curves were determined from (32)P appearance in the serum. The 1/2X dose of ferrihydrite reduced (32)P by approximately one half, and the 2X dose nearly completely suppressed (32)P absorption, similar to the 1X dose of calcium acetate. The advantage of using a ferrihydrite binder would be to avoid the hypercalcemia resulting from the use of high-dose calcium salts. An added advantage may result from the small amounts of iron absorbed in these chronically iron-deficient patients.

New phosphate binding agents: ferric compounds

Several prior studies suggest that ferric compounds bind dietary phosphate and possess clinical potential as phosphate binding agents. Therefore, this study was conducted to measure the effect of several ferric compounds on intestinal phosphate binding and absorption. Balance studies lasting 2 to 4 wk were performed in normal and azotemic (achieved by subtotal nephrectomy) rats maintained on a 1.02% phosphorus diet supplemented with ferric salts (formulated to 0.95% Fe) or no ferric salt (control). In rats with normal renal function (average creatinine clearance, 4.0 ml/min per kg), the average net intestinal absorption of phosphate over all balance periods was 103.3 mg/d for the control group versus 84.7 mg/d for the ferric citrate group (P < 0.005). In the azotemic rats (average creatinine clearance, 3.3 ml/min per kg), the average net intestinal absorption of phosphate over all balance periods was significantly lower for the three ferric groups than the control groups (P < or = 0.02): 95.3 mg/d for the control group versus 75.6 mg/d for the ferric ammonium citrate-treated group (P = 0.058), 77.0 mg/d for the ferric citrate-treated group (P = 0.057), and 62.5 mg/d for the ferric chloride-treated group (P < 0.002). Urinary phosphate excretion fell, sometimes to an even greater extent than did intestinal absorption, yielding no net reduction in phosphate balance in these growing, young animals with relatively preserved renal function. Calcium balance was largely unaffected by the ferric compounds. There were trends toward decreased serum phosphorus and parathyroid hormone concentrations and increased iron and hematocrit in the ferric-treated azotemic groups. All tested ferric compounds were well tolerated, but animal growth was stunted in the ferric chloride animals compared with the control group. Phosphate binding was estimated at 85 to 180 mg per gram of elemental iron, which is comparable to other phosphate binding agents. Ferric salts decrease net intestinal phosphate absorption and hold promise for the treatment of phosphate retention in patients with renal failure.

Role of calcium carbonate administration timing in relation to food intake on its efficiency in controlling hyperphosphatemia in patients on maintenance dialysis

A study has claimed that at an equal elemental calcium dose, CaCO3 was not less but equally as efficient in controlling predialysis hyperphosphatemia as calcium acetate, provided both calcium salts were ingested 5 min before meals instead of during meals because the higher acidity of the fasting gastric juice would allow for better dissociation of CaCO3. However, this study did not directly demonstrate that the efficiency of CaCO3 in controlling hyperphosphatemia was actually greater when it was administered before a meal than during a meal. To examine this point, we performed a 3 month randomized crossover trial in 12 reliable and stable patients maintained on chronic hemodialysis. Their plasma concentrations of calcium, protein, phosphate, bicarbonate, urea, and creatinine were measured before the first dialysis of each week and the amount of intact parathyroid hormone (PTH) at the beginning and at the end of each of the 3 months. Comparison of the plasma concentrations measured during the 2 modes of administration showed no significant differences in creatinine, urea, bicarbonate, or intact PTH. The mean (+/-SD) plasma concentration of PO4 was not significantly lower (1.88+/-0.50 vs. 1.74+/-0.41 mM) whereas the corrected level of plasma Ca was significantly lower (2.30+/-0.17 vs. 2.38+/-0.16 mM; p < 0.04) when CaCO3 was given before meals than during meals. In conclusion, the administration of CaCO3 before a meal does not increase its efficiency in controlling hyperphosphatemia because the level of plasma PO4 was actually slightly higher with this timing of administration whereas the comparison of the creatinine and urea levels suggested a stability of phosphate intake and the comparison of the PTH and bicarbonate levels suggested the stability of osteolysis and of the transcellular membrane shift of phosphate. Also, administration of CaCO3 before a meal is associated with significantly lower plasma corrected calcium, suggesting less absorption of calcium, which may be an advantage but only in hypercalcemic patients. There is no reason other than the prevention of its hypercalcemic effect to recommend the administration of CaCO3 just before meals rather than during meals.

Poly[allylamine hydrochloride] (RenaGel): a noncalcemic phosphate binder for the treatment of hyperphosphatemia in chronic renal failure

Dietary phosphate restriction and the oral administration of calcium and aluminum salts have been the principal means of controlling hyperphosphatemia in individuals with end-stage renal disease over the past decade. Although relatively well-tolerated, a large fraction of patients treated with calcium develop hypercalcemia, particularly when administered concurrently with calcitriol, despite a lowering of the dialysate calcium concentration. We evaluated the efficacy of cross-linked poly[allylamine hydrochloride] (RenaGel; Geltex Pharmaceuticals, Waltham, MA), a nonabsorbable calcium- and aluminum-free phosphate binder, in a randomized, placebo-controlled, double-blind trial of 36 maintenance hemodialysis patients followed over an 8-week period. RenaGel was found to be as effective as calcium carbonate or acetate as a phosphate binder. The reduction in serum phosphorus was significantly greater after 2 weeks of treatment with RenaGel (6.6 +/- 2.1 mg/dL to 5.4 +/- 1.5 mg/dL) compared with placebo (7.0 +/- 2.1 mg/dL to 7.2 +/- 2.4 mg/dL; P = 0.037). There was no significant change in serum calcium concentration in either treatment group. The total serum cholesterol and low-density lipoprotein cholesterol fraction were significantly reduced in RenaGel-treated patients compared with placebo-treated patients (P = 0.013 and P = 0.003, respectively) without a concomitant reduction in high-density lipoprotein cholesterol (P = 0.93). There was no difference among recipients of RenaGel and placebo in terms of adverse events. RenaGel is a safe and effective alternative to oral calcium for the management of hyperphosphatemia in end-stage renal disease.

Calcium acetate versus calcium carbonate as oral phosphate binder in pediatric and adolescent hemodialysis patients

Calcium carbonate is widely used as an oral phosphorus binder to control hyperphosphatemia in children on maintenance hemodialysis. Intestinal calcium absorption may induce hypercalcemia, particularly if calcitriol is given simultaneously. In adults, calcium acetate binds phosphorus more effectively than calcium carbonate, while reducing the frequency of hypercalcemic events. We therefore compared calcium acetate with calcium carbonate in nine pediatric patients on long-term maintenance hemodialysis. Following a 1-week withdrawal of phosphorus binders, calcium carbonate was administered for 7 weeks; after a second withdrawal, calcium acetate was given for another 7 weeks. All patients received calcitriol regularly. Both agents lowered the serum phosphorus concentration significantly (calcium carbonate 5.7 +/- 1.4 vs. 7.7 +/- 2.1 mg/ dl, P < 0.005; calcium acetate 5.8 +/- 1.4 vs. 7.8 +/- 2.0 mg/dl, P < 0.005). Significantly less elementary calcium was ingested with calcium acetate than with calcium carbonate: 750 (375-1,500) vs. 1,200 (0-3,000) mg calcium/day, P < 0.0001. Wit calcium carbonate serum calcium increased significantly. The number of episodes of hyperphosphatemia or hypercalcemia did not differ between treatments. Intact plasma parathyroid hormone (PTH) decreased significantly with both phosphate binders, and serum 25-hydroxyvitamin D3 increased. There was a close relationship between serum phosphorus and PTH in prepubertal but not in pubertal patients. We conclude that hyperphosphatemia can be controlled effectively by both calcium acetate and calcium carbonate in pediatric hemodialysis patients. The oral load of elementary calcium is reduced significantly by binding phosphorus with calcium acetate instead of calcium carbonate; nevertheless, hypercalcemic episodes remain equally frequent with both phosphate binders.

The renal bone diseases in children treated with dialysis

Renal osteodystrophy represents a spectrum from high- to low-turnover bone lesions. The specific pattern, however, may change during selected therapeutic interventions. As in the past, osteitis fibrosa remains the most frequent histologic lesion in pediatric patients on dialysis, although recently the prevalence of low-turnover bone lesions without aluminum toxicity has been increasing in the pediatric population. This may be a consequence of aggressive calcitriol and calcium therapy. The different factors involved in the development of secondary hyperparathyroidism include hyperphosphatemia, hypocalcemia, altered vitamin D synthesis, impairments in parathyroid hormone (PTH) secretion and metabolism, and, recently, possible downregulation of renal PTH/PTH-rP messenger RNA receptor. New developments in molecular biology have demonstrated the relationship between vitamin D and PTH. The use of high-dose pulse intravenous, intraperitoneal, and oral calcitriol therapy has significantly decreased serum PTH levels and retarded the progression of osteitis fibrosa. These therapeutic interventions, however, may have led to the development of adynamic bone lesions. The impact of adynamic bone lesions in the young and growing skeleton remains to be determined.

Magnesium carbonate as a phosphorus binder: a prospective, controlled, crossover study

The use of calcium carbonate (CaCO3) to bind phosphorus (P) in chronic hemodialysis patients has been a popular tactic in the past decade. Nonetheless, problems with hypercalcemia decrease its usefulness, particularly in patients treated with calcitriol. A P binder not containing calcium (Ca) would be of value in these circumstances. In short-term studies, we showed that magnesium carbonate (MgCO3) was well-tolerated and controlled P and Mg levels when given in conjunction with a dialysate Mg of 0.6 mg/dl. We, therefore, performed a prospective, randomized, crossover study to evaluate if the chronic use of MgCO3 would allow a reduction in the dose of CaCO3 and yet achieve acceptable levels of Ca, P, and Mg. We also assessed whether the lower dose of CaCO3 would facilitate the use of larger doses of calcitriol. The two phases were MgCO3 plus half the usual dose of CaCO3 and CaCO3 alone given in the usual dose. It was found that MgCO3 (dose, 465 +/- 52 mg/day elemental Mg) allowed a decrease in the amount of elemental Ca ingested from 2.9 +/- 0.4 to 1.2 +/- 0.2 g/day (P < 0.0001). The Ca, P, Mg levels were the same in the two phases. The maximum dose of i.v. calcitriol without causing hypercalcemia was 1.5 +/- 0.3 micrograms/treatment during the MgCO3 phase and 0.8 +/- micrograms/treatment during the Ca phase (P < 0.02). If these studies are confirmed, the use of MgCO3 and a dialysate Mg of 0.6 mg/dl may be considered in selected patients who develop hypercalcemia during treatment with i.v. calcitriol and CaCO3.

Characterization and extracorporeal application of a new phosphate-binding agent

A new phosphate-binding agent which does not cause any severe side effects in vivo was developed by modifying a crosslinked dextran with polynuclear iron(III)oxide-hydroxide. Its particle size ranges from 150 to 300 microns, and the iron content was about 18% by dry weight. The oxidation state of iron was characterized by ESCA and Mössbauer spectroscopy. The maximum phosphate binding capacity of the iron(III)oxide-hydroxide-modified dextran was determined with respect to aqueous phosphate solutions, human serum and whole blood. The effects on whole blood count, haemolysis, protein concentration and enzyme activities were examined. In addition, the influence of phosphate concentration, pH and temperature on the phosphate uptake of the material was determined. The results show that this new adsorbent might provide an alternative to conventional phosphate-binding agents. This paper also describes the first experiments on the therapeutic application of the material in an extracorporeal blood perfusion system for the treatment of hyperphosphataemia during haemodialysis.

Efficient phosphate binding using a combination of gluconolactate and carbonate calcium salts

Although renal-failure-related hyperphosphataemia can be corrected by various phosphate binders, there remains a need for safer and more efficient formulations to precipitate phosphate. This work describes both a theoretical approach and a phosphate precipitation test in order to design efficient binding calcium salts formulations. The results show that the combination of a soluble calcium salt (the gluconolactate) and a proton-consuming calcium salt (the carbonate) can precipitate phosphate effectively. Furthermore, the theoretical computations correlate well with the ability of the salt to bind phosphate in vitro.

Effect of D-glucose on intestinal permeability and its passive absorption in human small intestine in vivo

BACKGROUND

Based on studies in animals, it has been proposed that carrier-mediated D-glucose absorption markedly enhances passive permeability of the jejunal mucosa, allowing the majority of D-glucose absorption to proceed passively. In this study, we evaluated this hypothesis in the human jejunum in vivo.

METHODS

Using the constant perfusion, nonabsorbable marker technique, permeability of jejunal mucosa was assessed by measuring the ratio of diffusion rates of urea/L-xylose and mannitol/L-xylose. Passive D-glucose absorption was quantitated using L-glucose and mannitol as probes for D-glucose.

RESULTS

Addition of D-glucose to perfused solutions did not change the diffusion ratios, indicating that D-glucose has no effect on the size of channels for passive diffusion across the jejunal mucosa. The fraction of total D-glucose absorption that could be attributed to a passive mechanism averaged 5%. In the human ileum in vivo, we detected no evidence of passive D-glucose absorption.

CONCLUSIONS

Carrier-mediated D-glucose absorption does not increase passive permeability of human jejunal mucosa to solutes with molecular radii between 2.6 and 4.0 A. The amount of D-glucose absorbed passively from the human jejunum is trivial compared with the overwhelmingly dominant mechanism, carrier-mediated transport. Our results do not support the concept that sodium-dependent nutrient transport increases tight junction permeability.

Southwestern Internal Medicine Conference: bone disease in kidney failure: diagnosis and management

Recent technologic and therapeutic advances have improved the life of the patient with end-stage renal disease. High efficiency and high-flux hemodialyzer membranes have shortened the time required to dialyze, and recombinant erythropoietin has all but eliminated anemia as a major cause of morbidity, but the problem of renal osteodystrophy remains. The following discussion examines the spectrum of bone and joint disease in the patient with end-stage renal disease. The diagnostic and therapeutic strategies currently being tried in the management of these disorders are discussed.

Mechanism of phosphate adsorption to a three-dimensional structure of boehmite in the presence of bovine serum albumin

A new microcrystalline boehmite (tentatively named PT-A) was synthesized as an efficient phosphate adsorbent to replace aluminum hydroxide gel. The characteristic structure of PT-A was examined by nitrogen adsorption/desorption, X-ray diffraction, deviation microscopy, and scanning electron microscopy to establish a pore structural model of PT-A. With this model structure, the details of the mechanism of interaction between PT-A and phosphate in the presence of bovine serum albumin (BSA) are discussed. PT-A is a spherical particle with a diameter of approximately 100 microns and a porous surface structure, and its inside is packed with boehmite microcrystals (crystallite size, 2 nm). PT-A has three types of pores in its structure: a micropore with a narrow size-distribution, a mesopore with a broad size-distribution, and a macropore (radii of pores are 0.7, 1-20, and approximately 300 nm, respectively). When phosphate was incubated with PT-A in human gastric and intestinal juices or in an aqueous solution containing BSA, the amounts of phosphate adsorbed by PT-A were not affected by the presence of proteins. The nitrogen adsorption/desorption isotherms and energy dispersive X-ray analyses demonstrated that phosphate could diffuse to the smaller tunnels freely even if the external surface of PT-A was covered with BSA. It was also demonstrated that the main site of adsorption for phosphate was in micropores of PT-A, whereas BSA was adsorbed only to the external surface and none entered inside smaller tunnels consisting of micro- and mesopores.

Continuous ambulatory peritoneal dialysis: a review of its mechanics, advantages, complications, and areas of controversy

OBJECTIVE

The primary objective of this article is to review the mechanics, advantages, complications, pharmacokinetics, and future trends of continuous ambulatory peritoneal dialysis (CAPD) as they pertain to pharmacotherapy.

DATA SOURCES

Pertinent articles were obtained from an English-language literature search using MEDLINE (1980-1991), Index Medicus (1987-1990), and bibliographic reviews of review articles. Indexing terms included peritoneal dialysis, pharmacokinetics, peritonitis, vancomycin, and fluoroquinolones.

DATA SYNTHESIS

All clinical studies comparing organism recovery methods and treatment of peritonitis have methodologic limitations (e.g., comparison of disparate patient groups, different definitions of peritonitis, lack of follow-up, lack of control for sterile cultures) that may affect the reported results.

CONCLUSIONS

CAPD is an alternative to hemodialysis for the treatment of endstage renal disease and has many complications, leading to significant morbidity. This indicates that CAPD is not appropriate for all patients. Using blood-culturing techniques to culture for dialysate is most productive, but also the most costly. There are few data to indicate exactly the drugs, doses, and durations of choice for peritonitis. Both intraperitoneal and oral administration appear to be appropriate.

Aluminum toxicity in childhood

Aluminum intoxication is an iatrogenic disease caused by the use of aluminum compounds for phosphate binding and by the contamination of parenteral fluids. Although organ aluminum deposition was noted as early as 1880 and toxicity was documented in the 1960s, the inability to accurately measure serum and tissue aluminum prevented delineation of its toxic effects until the 1970s. Aluminum toxicity has now been conclusively shown to cause encephalopathy, metabolic bone disease, and microcytic anemia.

Reduced risk of hypercalcemia for hemodialysis patients by administering calcitriol at night

Renal osteodystrophy therapy in dialysis patients with calcitriol and intestinal phosphate binders containing calcium entails the risk of hypercalcemia. A study was performed using 35 hemodialysis patients to see whether the time of day when calcitriol is administered influences the incidence of hypercalcemia. It was shown that simply by administering at night (11:00 PM), the occurrence of hypercalcemia was significantly reduced. While greater than 80% of patients developed hypercalcemia when calcitriol was administered in the morning, when administered at night, this figure was only 50% (P less than 0.013). At the same time, the extent of hypercalcemia when calcitriol was administered at night was significantly lower than when it was administered in the morning. The incidence of hypercalcemia occurred regardless of the type of phosphate binder containing calcium used, whether it was calcium acetate or calcium carbonate. In addition, hypercalcemic episodes were always associated with hyperphosphatemia. On the basis of the above information, it would be expedient to administer calcitriol at night to dialysis patients, in order to reduce the risk of hypercalcemia and to preserve the hypophosphatemic effect of the applied intestinal phosphate binders.

Hyperphosphatemia: its consequences and treatment in patients with chronic renal disease

Control of phosphorus accumulation in chronic renal insufficiency is crucial to the prevention of secondary hyperparathyroidism and metastatic calcification. In early renal failure, calcitriol levels are normal and parathyroid hormone levels are elevated. The phosphorus levels are maintained in the normal range by the phosphaturia induced by hyperparathyroidism. In this situation, dietary phosphorus restriction increases calcitriol levels and suppresses parathyroid hormone secretion. As renal failure progresses into late stages, hyperphosphatemia is evident along with low levels of calcitriol and worsening hyperparathyroidism. Phosphorus restriction will not affect calcitriol concentrations, yet parathyroid levels may decline. During long-term dialysis, urinary excretion of phosphorus is usually minimal. Therefore, phosphorus balance is determined primarily by the net amount absorbed by the bowel and the quantity removed during dialytic therapy. Given an adequate diet, no form of conventional dialysis is able to fully compensate for the gastrointestinal absorption of phosphorus. Hence, compounds that bind phosphorus in the bowel are often necessary. With the realization that the use of phosphorus binders containing aluminum leads to aluminum accumulation and its sequelae: osteomalacia, dementia, myopathy, and anemia, other phosphorus binders have been evaluated. Calcium carbonate has been investigated the most thoroughly and is in wide use. It is inexpensive and contains a high percent of elemental calcium. However, it is only modestly potent in the binding of phosphorus, and large doses are often necessary to attain satisfactory control of phosphorus. This may lead to hypercalcemia. One approach to this problem is to decrease the concentration of calcium in the dialysate. Alternatively, a more effective phosphorus binder may be used. Calcium acetate has been shown in acute studies to have twice the binding capacity of phosphorus per calcium absorbed than calcium carbonate. Whether use of this compound decreases the incidence of hypercalcemia is unproven. Calcium citrate increases the gastrointestinal absorption of aluminum and offers no advantage over calcium carbonate. Other compounds, such as calcium ketoacids and calcium alginate, have not been extensively studied and are not generally available. The use of phosphorus binders containing magnesium in conjunction with a dialysate low in magnesium may be efficacious. Large doses of magnesium will cause diarrhea and thus limit its use as a single agent. Reasons for failure to control hyperphosphatemia include poor compliance, improper prescription of binders, poor dissolution rates seen with some generic brands of calcium carbonate, and the presence of severe hyperparathyroidism. Optimal control of serum phosphorus in dialysis patients should always be viewed in the context of adequate nutrition and protein intake.

Treatment of uraemic hyperphosphatemia with calcium acetate: a safe alternative to calcium carbonate

Clinical usefulness of calcium acetate (CAA) as phosphorus binder was assessed in 19 stable hemodialysis patients with persistent hyperphosphatemia. All were dialysed thrice weekly with a constant dialytic schedule and a dialysate calcium of 3.5 mEq/l. One month prior the study beginning all patients stopped assumption of Ca and vitamin D supplements. In the first period of the study CAA (mean daily doses 2.2 g) was administered for one month followed by 15 days of withdrawal. The mean serum phosphorus decreased from 7.6 +/- 1.4 to 5.8 +/- 0.8 mg% (p < 0.005). After 15 days of withdrawal mean serum phosphorus reached the pretreatment value. Then the patients entered a long term study with personalized doses of CAA (between 1 and 4 g/day) and administration in 8 of them of alpha-calcidol. After a mean follow-up period of 5.4 +/- 1.5 months serum phosphorus was reduced from 7.5 +/- 1.1 to 5.6 +/- 1.1 mg% (p < 0.0005) while calcemia increased from 9.0 +/- 0.7 to 9.6 +/- 0.6 mg% (p < 0.005). Only one patient developed mild hypercalcemia. We concluded that CAA is a safe alternative to calcium carbonate for the control of hyperphosphatemia of uraemic patients for the most efficient phosphorus binding and the lesser absorption of calcium.

Comparisons of the effects of calcium carbonate and calcium acetate on zinc tolerance test in hemodialysis patients

Because aluminum hydroxide, as a phosphate binder, lowered intestinal zinc absorption, we studied the effects of calcium carbonate (CaCO3) and calcium acetate (CaAc), two other phosphate binders, on intestinal Zn absorption in nine patients on hemodialysis and in 11 controls by measuring 1- and 2-hour serum Zn levels after oral administration of 50 mg of elemental Zn as Zn gluconate with or without concomitant administration of 2 g CaCO3 (800 mg elemental Ca) or 3 g CaAc (750 mg elemental Ca). Fasting serum Zn levels were not different between patients and controls (14.0 +/- 2.3 v 14.1 +/- 1.2 mumol/L [91.8 +/- 14.9 v 92.3 +/- 8.0 micrograms/dL]), but the area under the curve of serum Zn increment (AUC) 2 hours after an oral Zn challenge without or with either of two of phosphate binders used was significantly smaller in patients than in controls (P less than 0.05). The AUC after concomitant administration of Zn with CaCO3 did not differ from that of Zn alone in either patients or controls, but it was significantly less in Zn with CaAc than in Zn alone or in Zn with CaCO3 in both groups. The results demonstrate that intestinal Zn absorption after an oral Zn challenge decreased in patients on hemodialysis and concomitant administration of CaAc, but CaCO3 did not decrease intestinal Zn absorption in either group.

Uremic tumoral calcinosis: preliminary observations suggesting an association with aberrant vitamin D homeostasis

Periarticular tumoral calcification is a unique form of soft tissue calcification that occurs infrequently in patients with end-stage renal disease. The mechanism underlying such massive periarticular calcifications is unknown. The radiographic similarity between uremic tumoral calcifications and those found in hereditary tumoral calcinosis, a disorder of calcitriol and phosphorus homeostasis, caused us to examine whether abnormalities in vitamin D metabolism were associated with uremic calcinosis as well. We examined two uremic subjects with massive periarticular tumoral calcifications and found that they had inappropriately high serum calcitriol levels for the degree of renal function, hyperparathyroidism, and hyperphosphatemia. The source of calcitriol could not be identified in one subject, but likely was derived from granulomatous tissue in the other. In the subject with marrow granulomas, we found that calcitonin administration further stimulated calcitriol production. Although epidemiological studies are needed to confirm this preliminary association between calcitriol and uremic tumoral calcinosis, our observations suggest that normal serum calcitriol levels in association with hyperphosphatemia may be a contributing factor in the development of this rare disorder.

Calcium citrate markedly enhances aluminum absorption from aluminum hydroxide

The effect of calcium citrate on intestinal aluminum absorption, assessed by the increment in urinary aluminum excretion, was evaluated in eight normal men. Baseline urinary aluminum excretion was determined for 2 days; thereafter, subjects ingested aluminum hydroxide for 3 days. In a cross-over study, subjects were given either calcium citrate, 950 mg four times a day, or placebo during the 3 days of aluminum hydroxide ingestion (2.4 g/d). Plasma aluminum levels were measured on the second control day and the third day of aluminum hydroxide ingestion. Baseline urinary aluminum excretion was 0.02 +/- 0.004 (6.5 +/- 1.1 micrograms/g creatinine) and 0.03 +/- 0.005 mumol/mmol creatinine (7.4 +/- 1.3 micrograms/g creatinine). These values increased during aluminum hydroxide therapy, but values were much greater when calcium citrate was ingested with aluminum hydroxide. On 3 consecutive days, urinary aluminum excretion levels were 11.1 +/- 3.23, 8.8 +/- 2.9, and 5.3 +/- 0.7 times greater during the administration of calcium citrate with aluminum hydroxide than with aluminum hydroxide alone. Plasma aluminum levels did not differ in the two treatment groups. Thus, calcium citrate markedly enhances the absorption of aluminum from aluminum hydroxide and the two must not be prescribed together in patients with renal failure.

Calcium acetate control of serum phosphorus in hemodialysis patients

Calcium acetate has many characteristics of an ideal phosphorus binder. It is a readily soluble salt that avidly binds phosphorus in vitro at pH 5 and above. One-dose/one-meal balance studies show it to be more potent than calcium carbonate or calcium citrate. We studied chronic (3-month) phosphorus binding with calcium acetate in 91 hyperphosphatemic dialysis patients at four different centers. All phosphorus binders were stopped for 2 weeks. Calcium acetate at an initial dose of 8.11 mmol (325 mg Ca2+) per meal was then used as the only phosphorus binder. Dose was adjusted to attempt control of predialysis phosphorus level less than 1.78 mmol/L (5.5 mg/100 mL). Final calcium acetate dose was 14.6 mmol (586 mg) Ca2+ per meal. Sixteen patients developed mild transient hypercalcemia (mean, 2.84 mmol/L [11.4 mg/dL]. Initial phosphorus values in mmol/L (mg/dL) were 2.39 (7.4); at 1 month, 1.91 (5.9); and at 3 months, 1.68 (5.2). Initial calcium values in mmol/L (mg/dL) were 2.22 (8.9); at 1 month, 2.37 (9.5); and at 3 months, 2.42 (9.7). Initial aluminum values in mumol/L (micrograms/L) were 2.99 (80.7); and at 3 months were 2.54 (68.4). Initial C-terminal parathyroid hormone (C-PTH) values in ng/mL were 14.6; at 1 month, 11.9; and at 3 months, 13.2. Sixty-nine patients then entered a double-blind study. Phosphorus binders were stopped for 1 week. Calcium acetate (at a dose established in a prior study) or placebo was then administered for 2 weeks. Next, patients were crossed to the opposite regimen for 2 weeks. Initial phosphorus was 2.36 mmol/L (7.3 mg/100 mL) and calcium 2.22 mmol/L (8.9 mg/100 mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum accumulation during treatment with aluminum hydroxide and dialysis in children and young adults with chronic renal disease

BACKGROUND

The control of hyperphosphatemia is a major clinical problem in patients with chronic renal failure receiving regular dialysis treatment. Despite continuing concern about aluminum toxicity, aluminum-containing antacids are still used in many of these patients as phosphate-binding agents. Although maximal acceptable doses of aluminum hydroxide have been recommended, the safety and efficacy of these guidelines have not been evaluated.

METHODS

Seventeen children and young adults (mean [+/- SD] age, 14.1 +/- 3.7 years) undergoing regular peritoneal dialysis were randomly assigned to treatment with either aluminum hydroxide (n = 7; maximal dose, 30 mg per kilogram of body weight per day) or calcium carbonate (n = 10; dose range, 2.5 to 12 g per day, according to serum phosphorus levels). Aluminum retention was assessed by serial measurements of plasma aluminum, deferoxamine-infusion tests, and measurements of bone aluminum content during a mean (+/- SD) follow-up of 13 +/- 2 months. The evolution of bone disease was also evaluated.

RESULTS

Plasma aluminum levels and the increment in plasma aluminum after infusion of deferoxamine increased from base-line values in the patients treated with aluminum hydroxide, and aluminum-related bone disease developed in one patient. Serum phosphorus levels remained higher and serum calcium levels lower in the patients receiving aluminum hydroxide than in those receiving calcium carbonate. The skeletal lesions of secondary hyperparathyroidism improved in 7 of 10 patients receiving calcium carbonate but persisted or progressed in 6 of 7 patients given aluminum hydroxide (P less than 0.025).

CONCLUSIONS

Aluminum hydroxide is less effective than calcium carbonate as a phosphate-binding agent for the control of hyperphosphatemia and is associated with aluminum retention in children and young adults with chronic renal failure who are receiving dialysis therapy.

Calcium carbonate as a phosphate binder in dialysis patients: evaluation of an enteric-coated preparation and effect of additional aluminium hydroxide on hyperaluminaemia

Calcium carbonate has been successfully used as a phosphate binder in patients with chronic renal failure; however, a high frequency of hypercalcaemia has been reported. To study the effects of calcium carbonate preparations with different dissolution characteristics on the incidence of this side effect, we conducted a double-blind, crossover trial in 21 patients undergoing chronic haemodialysis. Aluminum hydroxide therapy was replaced with calcium carbonate. The subjects then randomly received either an enteric-coated or a gastric-coated preparation. Calcium carbonate (3.1-3.6 g/d) controlled serum phosphate concentrations as effectively as aluminium hydroxide (2.9 g/d). Concurrently, there was a significant rise in mean serum calcium and a fall in serum concentrations of both parathyroid hormone and osteocalcin, the latter suggesting a decrease in bone turnover. Overall, hypercalcaemic episodes developed in 9 patients (43%) and occurred at a considerable frequency (33 episodes per 100 patient-months) during treatment with the gastric-coated formulation. Following conversion to enteric-coated calcium carbonate (3.6 g/d) patients had fewer occurrences of hypercalcaemia (12 episodes per 100 patient-months, P less than 0.05) and, as compared to the gastric-coated preparation, increases in serum calcium greater than 3.00 mmol/l were not observed at all. Hyperaluminaemia was regressive during therapy with calcium carbonate, but addition of small doses of aluminium hydroxide caused a large rise in serum aluminium concentrations after infusion of desferrioxamine, indicating an enhanced rate of absorption or aberrant compartmentalization of aluminium. We conclude that calcium carbonate can control hyperphosphataemia in dialysis patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of calcium acetate or calcium citrate on intestinal aluminum absorption

The risk of aluminum (Al) accumulation in patients with chronic renal failure has led to use of non-Al phosphate binders. Frequently, Al and non-Al phosphate binders are co-administered. Unfortunately, calcium citrate (Ca citr), when given with Al-gel, markedly enhances Al absorption. To determine whether calcium acetate (Ca acetate) also augments Al absorption, 10 normal volunteers were each given orally, three-day courses of the following drug combinations dosed four times daily: 1) aluminum hydroxide gel (Al[OH]3) (5 ml) alone; 2) Al[OH]3 (5 ml) plus Ca acetate (1330 mg); 3) Al[OH]3 (5 ml) plus Ca citr (950 mg). A nine day wash-out occurred between each course. Al levels were measured using flameless atomic absorption spectrophotometry. Daily urine Al excretion was measured during a two-day baseline before each course and during each three-day drug course. Plasma Al was obtained during each baseline and drug course. Mean 24-hour Al excretion (micrograms/g creatinine/day) at baseline versus treatment for each combination was: 1) 5.9 +/- 3.2 versus 42.0 +/- 40.7 (mean +/- SD); 2) 5.7 +/- 3.0 versus 40.3 +/- 28.6: 3) 6.3 +/- 3.4 versus 175.8 +/- 103.3. Al excretion was significantly greater with combination 3 than with either 1 or 2 (P less than 0.05). The difference between 1 and 2 was not significant. Plasma Al (micrograms/liter) at baseline versus treatment for each combination was: 1) 5.3 +/- 4.2 versus 8.1 +/- 2.5 (mean +/- SD); 2) 3.1 +/- 2.2 versus 7.3 +/- 2.9; 3) 3.0 +/- 2.3 versus 12.0 +/- 6.1.(ABSTRACT TRUNCATED AT 250 WORDS)