Dietary phosphorus regulates serum fibroblast growth factor-23 concentrations in healthy men

CONTEXT

Fibroblast growth factor 23 (FGF-23) is important in the regulation of phosphorus and vitamin D metabolism. States of excess circulating FGF-23 are associated with renal phosphate wasting and inappropriately low serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] concentrations. Conversely, states of absent or biologically inactive circulating FGF-23 are associated with increased serum phosphorus and 1,25(OH)(2)D concentrations. Restriction of the dietary intake of phosphorus increases renal phosphate reabsorption and 1,25(OH)(2)D production, whereas the opposite occurs when dietary phosphorus is supplemented.

OBJECTIVE

We sought to determine whether serum FGF-23 concentration is regulated by dietary phosphorus and thereby mediates the physiological response of serum 1,25(OH)(2)D to changes in dietary phosphorus.

DESIGN, SETTING, AND PARTICIPANTS

We studied 13 healthy men as inpatients during a 4-wk dietary phosphorus intervention study.

INTERVENTION

Subjects consumed a constant diet that provided 500 mg of phosphorus per day, which was supplemented to achieve three phosphorus intakes, each of 9 d: 1) control = 1500 mg/d; 2) supplemented = 2300 mg/d; 3) restricted = 625 mg/d. Intakes of calcium, sodium, potassium, magnesium, and energy were constant.

MAIN OUTCOME MEASURE

Serum FGF-23, 1,25(OH)(2)D, phosphorus, and calcium concentrations were measured.

RESULTS

Serum FGF-23 concentrations decreased significantly from 30.7 +/- 8.7 pg/ml during phosphorus supplementation to 19.6 +/- 7.0 pg/ml during phosphorus restriction. Serum 1,25(OH)(2)D concentrations increased significantly from 29 +/- 10 pg/ml (75 +/- 26 pmol/liter) during phosphorus supplementation to 40 +/- 16 pg/ml (104 +/- 42 pmol/liter) during phosphorus restriction (P < 0.001). Serum 1,25(OH)(2)D concentrations varied inversely with those of serum FGF-23 (r = -0.67, P < 0.001).

CONCLUSIONS

We conclude that in healthy men, changes in dietary phosphorus within the physiological range of intakes regulate serum FGF-23 concentrations and suggest that dietary phosphorus regulation of 1,25(OH)(2)D production is mediated, at least in part, by changes in circulating FGF-23.

Enhanced parathyroid function in essential hypertension: a homeostatic response to a urinary calcium leak

Disorders of calcium metabolism are not generally considered important either clinically or pathophysiologically in essential hypertension. Recent reports, though, suggest that increased parathyroid gland function may be one of the more common endocrine disturbances associated with hypertension. We measured serum parathyroid hormone (PTH) concentrations as well as routine blood and urine chemistries in 34 hypertensives. Their mean PTH, 79.1 +/- 3.1 muliter Eq/muliter, was significantly higher (p less than 0.025) than the mean PTH, 66.9 +/- 3.3, of an age- and sex-matched normotensive control population. The mean serum calcium, 9.5 +/- 0.1 mg%, was identical in the two populations. Compared to a second age- and sex-matched normotensive population, the hypertensives demonstrated a significant (p less than 0.005) relative hypercalciuria. For any level of urinary sodium, hypertensives excreted more calcium. These preliminary data suggest that parathyroid gland function may be enhanced in essential hypertension. This increased gland activity appears, in part, to be an appropriate, physiologic response to a previously unrecognized relative hypercalciuria, or renal calcium leak, associated with essential hypertension. We conclude that the increased prevalence of hypertension in subjects with hyperparathyroidism probably represents the final event in a continuum that begins with obligatory urinary calcium losses in hypertensives, but whose pathological presentation is hyperparathyroidism. The results of this pilot study indicate a need for derivative experiments directed at defining the importance of our preliminary findings in the pathogenesis of human and experimental hypertension.

Impaired release of parathyroid hormone in magnesium deficiency

Parathyroid hormone release and end-organ responsiveness to parathyroid extract (PTE) were evaluated in a 25-year-old woman with magnesium deficiency associated with hypocalcemia and inappropriately low levels of serum immunoreactive parathyroid hormone (iPTH). End-organ responsiveness to PTE was demonstrated by increases in serum calcium and in urinary phosphorus, cyclic AMP, and hydroxyproline. When the serum calcium was increased from a baseline of 6.9 mg/100 ml to levels of 8.0 mg/100 ml and higher by calcium infusion, the serum iPTH decreased from the low normal range to below the limits of detectability. The intravenous administration of 3 mg/kg of body weight of magnesium led to an abrupt and striking increase in circulating iPTH with a 2-fold increase in one minute, a 6-fold increase in two minutes, and an 8-fold increase in five minutes. The very rapid increase in serum iPTH produced by magnesium infusion in this study suggests an effect of magnesium on hormone secretion rather than an effect on hormone synthesis. The evidence provided by this investigation indicates that the release of parathyroid hormone is impaired in magnesium deficiency and that the level of circulating calcium required for the suppression of parathyroid hormone secretion is lower than that in normal subjects.

Long-term treatment of hypoparathyroidism: a randomized controlled study comparing parathyroid hormone-(1-34) versus calcitriol and calcium

Hypoparathyroidism is one of the few remaining hormonal insufficiency states for which replacement therapy is unavailable. Previous short-term controlled trials have shown PTH to be a safe and effective treatment of hypoparathyroidism. In this randomized, parallel group, open-label trial, we compared synthetic human PTH-(1-34) (PTH) with conventional therapy, calcitriol and calcium, over a 3-yr period. Twenty-seven patients with confirmed hypoparathyroidism, aged 18-70 yr, were randomized to either twice daily sc PTH or oral calcitriol and calcium. The primary end points were calcium levels in serum and urine. Secondary end points were creatinine clearance, markers of bone turnover, and bone mineral density. Throughout the 3-yr study period, serum calcium levels were similar in both treatment groups within or just below the normal range. Mean urinary calcium excretion was within the normal range from 1-3 yr in PTH-treated patients, but remained above normal in the calcitriol group. Bone mineral content and bone mineral density showed no significant between-group differences over the 3-yr study period. We conclude that treatment with twice daily sc PTH provides a safe and effective alternative to calcitriol therapy and is able to maintain normal serum calcium levels without hypercalciuria for at least 3 yr in patients with hypoparathyroidism.

Effects of low-calcium diet on urine calcium excretion, parathyroid function and serum 1,25(OH)2D3 levels in patients with idiopathic hypercalciuria and in normal subjects

We have used a low-calcium diet providing only 2 mg/kg (body weight) per 24 hours of calcium to distinguish between "renal" and "absorptive" idiopathic hypercalciuria. Sixteen of 27 hypercalciuric subjects excreted calcium in excess of intake during days seven, eight and nine of he diet, suggesting some element of renal hypercalciuria; however, all patients had low or normal serum PTH and urine cAMP levels. In general, fasting urine calcium was elevated in these 16 subjects and normal in the remaining 11, who conserved calcium more normally. SErum 1,25(OH)2D3 levels were the same in patients and normal subjects, even though PTH levels of the patients were below those of he normal subjects. Urine magnesium excretion and phosphorus excretion were both increased in the patients who excreted calcium in excess of intake. Our findings suggest that renal and absorptive hypercalciuria may not be distinct entities but rather the two extremes of a continuum of behavior. A uniform elevation of intestinal calcium absorption and a variable defect of renal calcium reabsorption could explain our results far better than the hypothesis of distinct absorptive and renal forms of hypercalciuria.

The role of 1 alpha, 25-dihydroxyvitamin D in the mediation of intestinal hyperabsorption of calcium in primary hyperparathyroidism and absorptive hypercalciuria

The cuase for the intestinal hyperabsorptionof calcium (Ca) in various forms of hypercalciurias was explored by a careful measurement of plasma 1 alpha, 25-dihydroxycholecalciferol [1 alpha, 25-(OH)I D] and by an assessment of intestinal Ca absorption and of parathyroid function. In 18 cases of primary hyperparathyroidism (PHPT), the mean plasma concentration of 1 alpha, 25-(OH)2D was significantly increased (4.9 +/- 2.2 SD ng/dl vs. 3.4 +/- 0.9 ng/dl for the control group), and was significantly correlated with fractional Ca absorption (alpha) (r = 0.80, P less than 0.001). Plasma 1 alpha, 25-(OH)2D was also correlated with urinary Ca (P less than 0.05), but not with serum Ca or phosphorus (P), P clearance, urinary cyclic AMP, or serum immunoreactive parathyroid hormone. In 21 cases of absorptive hypercalciuria (AH), plasma 1 alpha, 25-(OH)2D was elevated in one-third of cases, and the mean value of 4.5 +/- 1.1 ng/dl was significantly higher than that of the control group (P less than 0.01). Since relative hypoparathyroidism may be present, the normal absolute value of plasma 1 alpha, 25-(OH)2D, found in two-thirds of cases of AH, may be considered to be inappropriately high. Moreover, in the majority of cases of AH, the data points relating plasma 1 alpha, 25-(OH)2D and alpha fell within 95% confidence limits of values found in non-AH groups (including PHPT). The results suggest that the intestinal hyperabsorption of Ca in PHPT aw AH may be vitamin D dependent. However, the disturbance in vitamin D metabolism may not be the sole cause for the high Ca absorption in AH, since in some patients with AH, the intestinal Ca absorption appears to be inapp

Oral intake of phosphorus can determine the serum concentration of 1,25-dihydroxyvitamin D by determining its production rate in humans

Changes in the oral intake of phosphorus could induce the reported changes in the serum concentration of 1,25-dihydroxyvitamin D (1,25-(OH)2D) by inducing changes in its production rate (PR) or metabolic clearance rate (MCR), or both. To investigate these possibilities, we employed the constant infusion equilibrium technique to measure the PR and MCR of 1,25-(OH)2D in six healthy men in whom the oral intake of phosphorus was initially maintained at 1,500 mg/70 kg body weight per d for 9 d, then restricted to 500 mg/d (coupled with oral administration of aluminum hydroxide) for 10 d, and then supplemented to 3,000 mg/d for 10 d. With phosphorus restriction, the serum concentration of 1,25-(OH)2D increased by 80% from a mean of 38 +/- 3 to 68 +/- 6 pg/ml, P less than 0.001; the PR increased from 1.8 +/- 0.2 to 3.8 +/- 0.6 micrograms/d, P less than 0.005; the MCR did not change significantly. The fasting serum concentration of phosphorus decreased from 3.5 +/- 0.2 to 2.6 +/- 0.2 mg/dl, P less than 0.01. With phosphorus supplementation, the serum concentration of 1,25-(OH)2D decreased abruptly, reaching a nadir within 2 to 4 d; after 10 d of supplementation, the mean concentration of 27 +/- 4 pg/ml was lower by 29%, P less than 0.01, than the value measured when phosphorus intake was normal. The PR decreased to 1.3 +/- 0.2 micrograms/d, P less than 0.05; the MCR did not change significantly. The fasting serum concentration of phosphorus increased significantly, but only initially. These data demonstrate that in healthy men, reductions and increases in the oral intake of phosphorus can induce rapidly occurring, large, inverse, and persisting changes in the serum concentration of 1,25-(OH)2D. Changes in the PR of 1,25-(OH)2D account entirely for the phosphorus-induced changes in serum concentration of this hormone.

Low-cost struvite production using source-separated urine in Nepal

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH(4)PO(4)·6H(2)O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160±50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.

Milk production, reproductive performance, and fecal excretion of phosphorus by dairy cows fed three amounts of phosphorus

Milk production was measured and phosphorus (P) excretion in feces was estimated in dairy cows fed three amounts of P. A basal diet was formulated to contain 0.31% P (DM basis). Sodium monophosphate replaced corn in the basal diet to give two additional diets containing 0.40 and 0.49% P. The diets were fed to eight, nine, and nine multiparous Holsteins from the beginning to the end of lactation. Milk yields for the 308-d lactation were 10,790, 11,226, and 11,134 kg for the three treatments, respectively. The lowest milk yield resulted from decreased milk production during late lactation with the 0.31% P group. Reproductive performance of the cows was not related to dietary P content. Fecal P concentration, determined in wk 2, 4, 6, 8, 23, and 40 of lactation, increased as dietary P intake was increased. Cows fed the lowest P diet conserved P by minimizing P excretion in feces and urine, whereas cows in the other two treatments excreted more P through these routes. A reduction in dietary P from 0.49 to 0.40% reduced fecal P excretion by 23%. Apparent P digestibilities of less than 40% are indicative of surplus dietary P. Feeding 0.40% P appeared sufficient to maintain P balance and the level of milk production achieved in this experiment. An example is given which illustrates the relationship between dietary and fecal P.

Vitamin D-resistant rickets associated with epidermal nevus syndrome: demonstration of a phosphaturic substance in the dermal lesions

A 5-year-old boy was found to have severe rickets in association with hyperpigmented, linear, verrucous, epidermal tumors, typical of the epidermal nevus syndrome. Normocalcemia (9.6 mg/dl), hypophosphatemia (2.0 mg/dl), elevated serum alkaline phosphatase concentration (313 IU), decreased renal tubular reabsorption of phosphorus (35%), radiologic evidence of rickets, and lack of response to usual therapeutic doses of vitamin D suggested hypophosphatemic vitamin D-resistant rickets. Therapy with vitamin D in doses to 750,000 IU and oral phosphate, 2.0 gm/day, failed to induce healing of the rickets. A subtotal parathyroidectomy performed when the patient was 9 years old was also without effect. When he was 12 years old several fibroangiomas on the face and left lower limb were excised. Within three months all biochemical abnormalities resolved and radiologic evidence of healing was observed. A portion of excised tissue was homogenized and injection of the supernate into a 6-week-old puppy induced excessive phosphaturia. The data suggest that the rickets was induced by a phosphaturic substance extractable from the tumors.

Urinary calcium excretion in familial hypocalciuric hypercalcemia. Persistence of relative hypocalciuria after induction of hypoparathyroidism

Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant trait comprising hypercalcemia, hypophosphatemia, parathyroid hyperplasia, and unusually low renal clearance of calcium. We evaluated the role of parathyroid hormone in the relative hypocalciuria of FHH and characterized the renal transport of calcium in this disorder using three previously hypercalcemic FHH patients with surgical hypoparathyroidism and three controls with surgical hypoparathyroidism. Intravenous infusion of calcium chloride in two patients with FHH and in three controls increased serum calcium from a mean basal of 5.0 to a mean peak of 6.8 meq/liter in two FHH patients and from 4.2 to 5.7 in three control subjects. Urinary calcium in a third FHH patient was studied without calcium infusion during recovery from hypercalcemia of vitamin D intoxication. At all serum concentrations of calcium, calcium clearance was lower in FHH than in controls; at base-line serum calcium, the ratio of calcium clearance to inulin clearance (C(Ca)/C(IN)) in FHH subjects was 32% of that in controls and decreased to 19% during hypercalcemia. Calcium infusion increased the ratio of sodium clearance to inulin clearance in controls from a base line of 0.020 to 0.053 at peak concentrations of calcium in serum, but did not affect this parameter in FHH (0.017 at base-line serum calcium vs. 0.019 at peak). When calcium infusion studies were performed (in two patients with FHH and one control) during administration of acetazolamide, a drug whose principal renal action causes inhibition of proximal transport of solute, C(Ca)/C(IN) in the patients with FHH was 29 and 7% of that of the control at base-line and peak serum calcium, respectively. In contrast, ethacrynic acid, a diuretic that acts in the ascending limb of the loop of Henle, increased C(Ca)/C(IN) more in the FHH patients than in the control subject; C(Ca)/C(IN) was 65% at base-line and 47% at peak serum calcium, compared with that of the control subject. The greater calciuric response to ethacrynic acid than to acetazolamide or calcium infusion alone in FHH indicates that a major renal locus of abnormal calcium transport in this disorder may be the ascending limb of the loop of Henle.Decreased clearance of calcium in patients with FHH and hypoparathyroidism when compared with hypoparathyroid controls indicates that relative hypocalciuria in FHH is not dependent on hyperparathyroidism. Since the parathyroid glands in FHH are not appropriately suppressed by calcium, this implies that FHH represents a disorder of abnormal transport of, and/or response to, extracellular calcium in at least two organs, parathyroid gland and kidney.

Combination teriparatide and raloxifene therapy for postmenopausal osteoporosis: results from a 6-month double-blind placebo-controlled trial

We compared combination treatment with teriparatide plus raloxifene with teriparatide alone in women with postmenopausal osteoporosis in a 6-month double-blind, placebo-controlled trial that measured biochemical markers of bone turnover and BMD. Markers of bone formation and spine BMD increased similarly with teriparatide alone and combination therapy. However, combination therapy induced a significantly smaller increase in bone resorption versus teriparatide alone and significantly increased total hip BMD versus baseline.

INTRODUCTION

The effects of combining two approved treatments for osteoporosis with different modes of action were examined by comparing teriparatide [rhPTH(1-34)] monotherapy with combination teriparatide and raloxifene therapy.

MATERIALS AND METHODS

A 6-month randomized, double-blind trial comparing teriparatide plus raloxifene (n = 69) versus teriparatide plus placebo (n = 68) was conducted in postmenopausal women with osteoporosis.

RESULTS

Bone formation (N-terminal propeptide of type 1 collagen [PINP]) increased similarly in both treatment groups. However, the increase in bone resorption (serum C-terminal telopeptide of type I collagen [CTx]) in the combination group was significantly smaller than in the teriparatide-alone group (p = 0.015). Lumbar spine BMD significantly increased 5.19 +/- 0.67% from baseline in the teriparatide-alone group. In the combination group, lumbar spine (6.19 +/- 0.65%), femoral neck (2.23 +/- 0.64%), and total hip (2.31 +/- 0.56%) BMD significantly increased from baseline to study endpoint, and the increase in total hip BMD was significantly greater than in the teriparatide-alone group (p = 0.04). In the teriparatide-alone group, mean serum calcium levels increased from baseline to endpoint (0.30 +/- 0.06 mg/dl, p < 0.001), whereas mean serum phosphate remained unchanged. In the combination group, mean serum calcium was unchanged, and mean serum phosphate decreased (-0.20 +/- 0.06 mg/dl, p < 0.001) from baseline to endpoint. Changes in serum calcium (p < 0.001) and phosphate (p < 0.004) were significantly different between treatment groups. The safety profile of combination therapy was similar to teriparatide alone.

CONCLUSIONS

Combination therapy increased bone formation to a similar degree as teriparatide alone. However, the increase in bone resorption was significantly less and total hip BMD significantly increased for combination therapy compared with teriparatide alone. Combination treatment with raloxifene may thus enhance the bone forming effects of teriparatide. Further studies over longer treatment duration that include fracture endpoints are necessary to fully ascertain the clinical significance of combination raloxifene plus teriparatide therapy in postmenopausal osteoporosis.

A rat model of chronic kidney disease-mineral bone disorder

Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) is a newly defined syndrome encompassing patients with chronic kidney disease that have a triad of biochemical alterations in calcium, phosphorus and parathyroid hormone, vascular calcification, and bone abnormalities. Here we describe a novel Cy/+ rat model of slowly progressive kidney disease spontaneously developing the three components of CKD-MBD when fed a normal phosphorus diet. Since the renal disorder progressed 'naturally' we studied the effect of dietary manipulation during the course of the disease. Animals with early, but established, chronic kidney disease were fed a casein-based or a grain-based protein diet both of which had equivalent total phosphorus contents. The two different sources of dietary protein had profound effects on the progression of CKD-MBD, likely due to differences in intestinal bioavailability of phosphorus. Although both dietary treatments resulted in the same serum phosphorous levels, the casein-fed animals had increased urinary phosphorus excretion and elevated serum FGF23 compared to the grain-fed rats. This model should help identify early changes in the course of chronic kidney disease that may lead to CKD-MBD.

Age-related changes in parathyroid hormone and parathyroid hormone action in normal humans

We evaluated parathyroid function in 158 normal subjects, aged 23-85 yr. Calcium, phosphorus, creatinine, and cAMP were measured in blood and urine in the fasting state and after a 1-g oral calcium challenge. Serum immunoreactive PTH (iPTH) was measured with a goat antiserum developed against human PTH, using (43Tyr) human PTH-(44-68) as tracer and standards. With age, a decrease in total serum Ca (r = -0.14; P less than 0.05) was attributable to a fall in serum albumin (r = -0.40; P less than 0.001). Creatinine clearance fell from 124 ml/min at age 20 yr to 61 ml/min at age 80 yr (r = -0.44; P less than 0.001). iPTH rose with age in men (r = 0.21; P less than 0.05) and women (r = 0.31; P less than 0.001) from 29 pg/ml at age 20 yr to 48 pg/ml at 80 yr. iPTH was also correlated with creatinine clearance (r = -0.32; P less than 0.001. When renal function was controlled in the analysis, the regression of iPTH with age was no longer significant. Other significant correlations with age include a decrease in renal phosphorus reabsorption (r = -0.17; P less than 0.05) and an increase in urinary nephrogenous cAMP excretion (r = 0.34; P less than 0.01). The rise in nephrogenous cAMP was not accompanied by a change in total urinary cAMP, since plasma, and therefore filtered, cAMP decreased with age. Basal calcium excretion was stable, but the calciuric response to oral calcium decreased (r = -0.27; P less than 0.01). We conclude that loss of renal function is the major cause of rising iPTH levels with age.

Physiological responses of human adults to foods containing phosphate additives

An experiment was conducted to assess the physiological effects of a diet rich in foods cotaining phosphate additives. During a 4-week control period, eight adults were fed a balanced diet free of phosphate additives providing approximately 95 g protein 0.7 g Ca and 1.0 g P per day. During a subsequent 4-week period, food items containing phosphate additives were substituted for counterpart items devoid of added phosphates. This diet contained 0.7 g Ca and 2.1 g P per day. The introduction of foods containing phosphate additives was associated with intestinal distress, soft stools or mild diarrhea. These symptoms subsided in six subjects but occurred intermittently throughout the experimental period in the other two subjects. The high-phosphorus diet induced increases in serum phosphorus and urinary phosphorus and decreases in serum calcium and urinary calcium. Hydroxyproline excretion in the urine was increased and cyclic AMP excretion was elevated in six of the eight subjects. These changes are analogous to those seen in experimental animals fed high-phosphorus diets which were shown to be due to enhanced parathyroid activity (secondary hyperparathyroidism). The use of phosphate food additives is discussed with respect to their possible stimulating effect on adult bone resorption.

Biological effects of short-term or prolonged administration of 9-[2-(phosphonomethoxy)propyl]adenine (tenofovir) to newborn and infant rhesus macaques

The reverse transcriptase inhibitor 9-[2-(phosphonomethoxy)propyl]adenine (PMPA; tenofovir) was previously found to offer strong prophylactic and therapeutic benefits in an infant macaque model of pediatric human immunodeficiency virus (HIV) infection. We now summarize the toxicity and safety of PMPA in these studies. When a range of PMPA doses (4 to 30 mg/kg of body weight administered subcutaneously once daily) was administered to 39 infant macaques for a short period of time (range, 1 day to 12 weeks), no adverse effects on their health or growth were observed; this included a subset of 12 animals which were monitored for more than 2 years. In contrast, daily administration of a high dose of PMPA (30 mg/kg subcutaneously) for prolonged periods of time (>8 to 21 months) to 13 animals resulted in a Fanconi-like syndrome (proximal renal tubular disorder) with glucosuria, aminoaciduria, hypophosphatemia, growth restriction, bone pathology (osteomalacia), and reduced clearance of PMPA. The adverse effects were reversible or were alleviated following either complete withdrawal of PMPA treatment or reduction of the daily regimen from 30 mg/kg to 2.5 to 10 mg/kg subcutaneously. Finally, to evaluate the safety of a prolonged low-dose treatment regimen, two newborn macaques were started on a 10-mg/kg/day subcutaneous regimen; these animals are healthy and have normal bone density and growth after 5 years of daily treatment. In conclusion, our findings suggest that chronic daily administration of a high dose of PMPA results in adverse effects on kidney and bone, while short-term administration of relatively high doses and prolonged low-dose administration are safe.