Cannabidiol safety considerations: Development of a potential acceptable daily intake value and recommended upper intake limits for dietary supplement use

Consumer use of hemp-derived products continues to rise, underscoring the need to establish evidence-based safety guidance. The present study sought to develop recommendations for oral upper intake limits of cannabidiol (CBD) isolate. Sufficiently robust and reliable data for this purpose were identified from published human clinical trials and guideline-compliant toxicity studies in animal models. Based on the metrics used in this assessment, a potential Acceptable Daily Intake (ADI) value of 0.43 mg/kg-bw/d (e.g., 30 mg/d for 70-kg adult) was determined for the general population based on liver effects in human studies. This value applies to the most sensitive subpopulations, including children, over a lifetime of exposure and from all sources, including food. For dietary supplements with adequate product labeling intended for use by healthy adults only, a potential Upper Intake Limit (UL) of 70 mg/d was determined based on reproductive effects in animals. For healthy adults, except those trying to conceive, or currently pregnant or lactating, a conservative dietary supplement UL of 100 mg/d was identified based on liver effects; however, as the target population excludes individuals at risk for liver injury, an alternative dietary supplement UL of 160 mg/d for this population can also be considered.

Toxicological Evaluation and Pain Assessment of Four Minor Cannabinoids Following 14-Day Oral Administration in Rats

Introduction: Despite growing consumer interest and market availability, the safety of minor cannabinoids, generally present in low concentrations in Cannabis sativa L., is not well understood. Materials and Methods: Cannabichromene (CBC; 3.2, 10, 17, 22, 32, or 100 mg/kg-bw/day), cannabinol (CBN; 1, 3.2, 10, 17, 32, or 100 mg/kg-bw/day), delta-8-tetrahydrocannabinol (D8-THC; 0.32, 1, 3.2, or 10 mg/kg-bw/day), tetrahydrocannabivarin (THCV; 3.2, 10, 17, 22, 32, or 100 mg/kg-bw/day), and vehicle (medium-chain triglyceride oil) preparations were administered via oral gavage once daily for 14 days to Sprague Dawley rats. Changes in behavior, body weight, food consumption, clinical pathology, organ weights, body temperature, and thermal pain sensitivity (tail flick assay) were assessed. Select organ tissues were collected at terminal necropsy and fixed for histopathological examination. Results: No treatment-related deaths were observed throughout the study, and cannabinoids were generally well tolerated. While some significant trends in body weight differences from controls (increases and decreases) were observed, these occurred independently of food consumption. Overall, differences in serum chemistry and hematology parameters between cannabinoid groups and their respective control groups were considered to occur due to biological variation among rats. No treatment-related gross abnormalities were observed in examined organs. Significant changes in absolute and relative organ weights occurred primarily in males and were generally of negligible magnitude. There were no biologically significant histopathological observations. While pain tolerance was significantly improved in animals treated with D8-THC (3.2 and 10 mg/kg-bw/day, day 14), results across minor cannabinoids were inconsistent and warrant further study. Conclusion: Minor cannabinoids were well tolerated across 14 days of daily oral administration at the doses assessed. Modest, dose-dependent trends in relative organ weights and serum chemistry parameters warrant exploration at higher oral doses. These data will assist in dose selection for future studies investigating the long-term safety and effects of CBC, CBN, D8-THC, and THCV.

Genotoxicity evaluation of cannabidiol

Consumer use of cannabidiol (CBD) for personal wellness purposes has garnered much public interest. However, safety-related data on CBD in the public domain are limited, including a lack of quality studies evaluating its genotoxic potential. The quality of available studies is limited due to the test material used (e.g., low CBD purity) and/or study design, leading some global regulatory agencies to highlight genotoxicity as an important data gap for CBD. To address this gap, the genotoxic potential of a pure CBD isolate was investigated in a battery of three genotoxicity assays conducted according to OECD testing guidelines. In an in vitro microbial reverse mutation assay, CBD up to 5000 μg/plate was negative in Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537, and Escherichia coli strain WP2 uvrA, with and without metabolic activation. Testing in an in vitro micronucleus assay was negative in human TK6 cells up to 10-11 μg/mL, with and without metabolic activation. Finally, an in vivo micronucleus assay conducted in male and female rats was negative for genotoxicity up to 1000 mg/kg-bw/d. Bioanalysis of CBD and its primary metabolite, 7-carboxy CBD, confirmed a dose-related increase in plasma exposure. Together, these assays indicate that CBD is unlikely to pose a genotoxic hazard.

Reproductive and developmental toxicity evaluation of cannabidiol

An important data gap in determining a safe level of cannabidiol (CBD) intake for consumer use is determination of CBD's potential to cause reproductive or developmental toxicity. We conducted an OECD Test Guideline 421 GLP-compliant study in rats, with extended postnatal dosing and hormone analysis, where hemp-derived CBD isolate (0, 30, 100, or 300 mg/kg-bw/d) was administered orally. Treatment-related mortality, moribundity, and decreased body weight and food consumption were observed in high-dose F₀ adult animals, consistent with severe maternal toxicity. No effects were observed on testosterone concentrations, F₀ reproductive performance, or reproductive organs. Hepatocellular hypertrophy in the 100- and 300 mg/kg-bw/day groups correlated with hypertrophy/hyperplasia in the thyroid gland and changes in mean thyroid hormone concentrations in F₀ animals. Mean gestation length was unaffected; however, total litter loss for two females and dystocia for two additional females in the high-dose group occurred. Other developmental effects were limited to lower mean pup weights in the 300 mg/kg-bw/d group than those of controls. The following NOAELs were identified for CBD isolate based on this study: 100 mg/kg-bw/d for F₀ systemic toxicity and female reproductive toxicity, 300 mg/kg-bw/d for F₀ male reproductive toxicity, and 100 mg/kg-bw/d for F₁ neonatal and F₁ generation toxicity.

Oral toxicity evaluation of cannabidiol

Use of cannabidiol (CBD) in humans has increased considerably in recent years. While currently available studies suggest that CBD is relatively safe for human consumption, data from publicly available studies on CBD conducted according to modern testing guidelines are lacking. In the current study, the potential for toxicity following repeated oral exposure to hemp-derived CBD isolate was evaluated in male and female Sprague Dawley rats. No adverse treatment-related effects were observed following administration of CBD via oral gavage for 14 and 90 days at concentrations up to 150 and 140 mg/kg-bw/d, respectively. Microscopic liver and adrenal gland changes observed in the 90-day study were determined to be resolved after a 28-day recovery period. CBD was well tolerated at these dose levels, and the results of this study are comparable to findings reported in unpublished studies conducted with other CBD isolates. The current studies were conducted as part of a broader research program to examine the safety of CBD.

Cannabidiol Safety Data: A Systematic Mapping Study

Robust assessment of potential adverse outcomes is needed to determine a safe cannabidiol (CBD) intake level for consumer use. To assist in identifying knowledge gaps and inform future decision making regarding systematic development of health-based benchmarks, we have developed the first systematic map of the safety-related information available for CBD in the peer-reviewed literature. Literature searching conducted according to a published protocol yielded a total of 4186 unique titles and abstracts published through 2020. These were screened using DistillerSR for studies that evaluated at least one potential health outcome following exposure to CBD and/or other hemp-derived substances. Additional categorization was conducted for a subset of 1001 studies in which CBD was administered alone. Studies that investigated CBD most frequently reported on neurological outcomes (532), carcinogenic outcomes (129), and pharmacokinetics (118). Less frequently studied categories included developmental and reproductive, hepatic, and gastrointestinal outcomes. The primary outcomes associated with the most adverse events reported in the literature were neurological (13) and developmental and reproductive (12). Based on the studies identified, reproductive and developmental toxicity was identified as a data gap that warrants conducting a well-designed, guideline-compliant reproductive toxicity study on CBD. In addition, immune outcomes were noted as a potential emerging research area for CBD. This systematic map provides an important baseline from which to identify topics that may be suitable for further research related to the safe use of CBD. Implications for future potential work and limitations of the mapping exercise are discussed.

Acute oral toxicity of nickel compounds

Acute oral toxicity studies were conducted on samples of nine unique nickel compounds and two complex materials to comply with the data and classification requirements of the new Registration, Evaluation, and Authorization of Chemicals Regulation (REACH) in Europe. The samples tested in this study confirmed the overall low oral toxicity of nickel substances and demonstrated a wide range of LD(50) values extending from 310 to >11,000 mg/kg. This variation highlights the differences in toxicological properties between various forms of nickel and underscores the importance of Ni(II) ion bioavailability in determining toxicity. The relative acute oral toxicity of the various nickel substances was found to be: nickel fluoride, nickel sulfate, nickel chloride, nickel acetate > nickel sulfamate > nickel hydroxycarbonate > nickel dihydroxide >> nickel subsulfide, nickel oxides, nickel ash, nickel mattes. Based on these data, four nickel compounds would receive a Category 4 acute toxicity classification according to the European Regulation on Classification, Labelling and Packaging of Chemical Substances and Mixtures (CLP), while the rest of the nickel substances tested fit the criterion for no classification. These data also provided the in vivo verification needed to perform read-across for additional oral toxicity endpoints and nickel substances.

Temperature effect on nickel release in ammonium citrate

Leaching in ammonium citrate has been extensively used to assess the fraction of water-soluble nickel compounds present in nickel producing and using workplace aerosols. Leaching in ammonium citrate according to the first step of the Zatka protocol was found to overestimate the water-soluble nickel fraction by more than ten-fold compared to synthetic lung fluid (37 degrees C), when nickel carbonate and subsulfide were present. These results suggest that exposure matrices based on this method should be reexamined. Leaching studies of refinery particles are needed to further clarify this important issue.

Peripheral intrapulmonary lipoma: a rare lung neoplasm

Lipomas are common benign tumours, but intrathoracic lipomas are rare and peripheral lung lipomas exceptionally rare. Seven cases--all in men--have been described in the world literature, diagnosed after thoracotomy and excision. We report a case of a peripheral intrapulmonary lipoma in a woman presenting as an opacity on a routine chest radiograph. The CT characteristics and the finding of the same lesion on reviewing a barium enema film from 12 years earlier allowed a confident diagnosis, avoiding the need for surgical excision. This is the first reported case of peripheral lung lipoma in a woman and highlights the value of reviewing previous radiographs.

Sex differences in cell migration in the preoptic area/anterior hypothalamus of mice

The preoptic area/anterior hypothalamus (POA/AH) sits as a boundary region rostral to the classical diencephalic hypothalamus and ventral to the telencephalic septal region. Numerous studies have pointed to the region's importance for sex-dependent functions. Previous studies suggested that migratory guidance cues within this region might be particularly unique in their diversity. To better understand the early development and differentiation of the POA/AH, cytoarchitectural, birthdate, immunocytochemical, and cell migration studies were conducted in vivo and in vitro using embryonic C57BL/6J mice. A medial preoptic nucleus became discernible using Nissl stain in males and females between embryonic days (E) E15 and E17. Cells containing immunoreactive estrogen receptor-alpha were detected in the POA/AH by E13, and increased in number with age in both sexes. From E15 to E17, examination of the radial glial fiber pattern by immunocytochemistry confirmed the presence of dual orientations for migratory guidance ventral to the anterior commissure (medial-lateral and dorsal-ventral) and uniform orientation more caudally (medial-lateral). Video microscopy studies followed the migration of DiI-labeled cells in coronal 250-microm brain slices from E15 mice maintained in serum-free media for 1-3 days. Analyses showed significant migration along a dorsal-ventral orientation in addition to medial-lateral. The video analyses showed significantly more medial-lateral migration in males than females in the caudal POA/AH. In vivo, changes in the distribution of cells labeled by the mitotic indicator bromodeoxyuridine (BrdU) suggested their progressive migration through the POA/AH. BrdU analyses also indicated significant movement from dorsal to ventral regions ventral to the anterior commissure. The significant dorsal-ventral migration of cells in the POA/AH provides additional support for the notion that the region integrates developmental information from both telencephalic and diencephalic compartments. The sex difference in the orientation of migration of cells in the caudal POA/AH suggests one locus for the influence of gonadal steroids in the embryonic mouse forebrain.

Special relationship of gamma-aminobutyric acid to the ventromedial nucleus of the hypothalamus during embryonic development

The ventromedial nucleus of the hypothalamus (VMH) is a key nucleus for regulating homeostatic, neuroendocrine, and behavioral functions. We conducted immunocytochemical analyses by using antisera directed against gamma-aminobutyric acid (GABA), its synthetic enzyme glutamic acid decarboxylase (GAD67), GABA-A receptor subunits (alpha2, beta3, epsilon), estrogen receptor-alpha, and Neuropeptide Y (NPY) in the region of the VMH in embryonic mice to identify potential patterning elements for VMH formation. Cells and fibers containing GABA and GAD67 encircled the primordial VMH as early as embryonic day 13 (E13) when the cytoarchitecture of the VMH was not recognizable by Nissl stain. At E16-17 the cytoarchitecture of the VMH became recognizable by Nissl stain as GABAergic fibers invaded the nucleus, continued postnatally, and by adulthood the density of GABAergic fibers was greater inside than outside the VMH. GABA-A receptor subunit expression (beta3 by E13 and alpha2 by E15) within the primordial VMH suggested potential sensitivity to the surrounding GABA signal. Brain slices were used to test whether fibers from distal or proximal sites influenced VMH development. Coronal Vibratome slices were prepared and maintained in vitro for 0-3 days. Nissl stain analyses showed a uniform distribution of cells in the region of the VMH on the day of plating (E15). After 3 days in vitro, cellular aggregation suggesting VMH formation was seen. Nuclear formation in vitro suggests that key factors resided locally within the coronal plane of the slices. It is suggested that either GABA intrinsic to the region nearby the VMH directly influences the development and organization of the VMH, or along with other markers provides an early indicator of pattern determination that precedes the cellular organization of the VMH.

Case report: splenic-gonadal fusion--the ultrasound appearances

We report the ultrasound appearances, with pathological correlation, of splenic-gonadal fusion in a patient who presented with an asymptomatic scrotal swelling. Ultrasound examination showed an echo-poor 2 cm diameter lesion in the upper pole of the left testicle. Histologically the lesion was normal spleen. Splenic-gonadal fusion should be considered in the differential diagnosis of scrotal swellings.

Autologous granulocyte scanning of painful prosthetic joints

To detect sepsis in the painful joint, autologous granulocytes labelled with indium-111 were used to scan 60 patients with 74 prosthetic joints. All 18 patients with confirmed sepsis had positive scans, that is, migration of granulocytes into the region of the prosthesis. Of the 22 sterile arthroplasties 20 had negative scans. In 34 cases there was good correlation between the clinical impression and the result of the scan. We suggest that indium granulocyte scintigraphy is a reliable method of detecting an infected prosthesis.

Indium-granulocyte scanning in the painful prosthetic joint

The value of indium-111-labeled granulocyte scanning to determine the presence of infection was assessed in 50 prosthetic joints (41 of which were painful) in 40 patients. Granulocytes were obtained from the patients' blood and labeled in plasma with indium 111 tropolonate. Abnormal accumulation of indium 111 in the region of the prosthesis was noted. Proven infection occurred in 11 prostheses, and all of the infections were detected by indium-111-labeled granulocyte scanning. Nineteen were not infected (including nine asymptomatic controls) and only two produced false-positive scans. This represents a specificity of 89.5%, sensitivity of 100%, and overall accuracy of 93.2%. These results compare favorably with plain radiography. There was no radiologic evidence of infection in three of the infected prostheses, and 10 of the noninfected prostheses had some radiologic features that suggested sepsis. We conclude that indium-granulocyte scanning can reliably detect or exclude infection in painful prosthetic joints and should prove useful in clinical management.

Paget's disease with benign osteopetrosis and Crohn's disease

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GDP binding to brown-adipose-tissue mitochondria of mice treated chronically with corticosterone

Cytochrome oxidase activity and mitochondrial GDP binding were decreased in brown adipose tissue of mice treated chronically with corticosterone. These changes occurred both in corticosterone-treated mice fed ad libitum and in treated mice pair-fed to control animals. Although the dietary stimulation of brown-adipose-tissue thermogenesis was suppressed by corticosterone, the acute response to cold was not affected.

Assessment of Viet Nam veterans for posttraumatic stress disorder in Veterans Administration disability claims

Since the Veterans Administration (VA) authorized compensation and other benefits for posttraumatic stress disorder, delayed type, in October 1980, the agency has received an increasingly large number of claims--mainly from Viet Nam veterans--for this disorder. An unprecedented challenge of the adequacy of psychiatric disability evaluation in the VA has thus been created. The authors describe efforts in one large program to meet this challenge and review 12 problems in the diagnostic process. Cooperation of all parties in claims transactions, thorough claimant assessment, reliance on DSM-III criteria and methods and consultation with examiners are essential principles for this work.

Cyclosporin A in cadaveric organ transplantation

The use of cyclosporin A (CyA) with a protocol designed to avoid the effects of nephrotoxicity resulted in a one-year survival of 86% in recipients of renal allografts from unmatched cadaveric donors. The drug also controlled rejection of liver and pancreatic allografts. It was possible to change patients initially treated with CyA to azathioprine and corticosteroids and vice versa, thus enlarging the potential value of CyA in organ allografting. Of 34 recipients of renal allografts, 29 were currently receiving only CyA as immunosuppressive treatment. Twelve patients never required any adjuvant steroid treatment. These results suggest that CyA is an effective immunosuppressant, and if used with care side effects need not be severe.

Cyclosporin A initially as the only immunosuppressant in 34 recipients of cadaveric organs: 32 kidneys, 2 pancreases, and 2 livers

34 patients treated with cyclosporin A received 36 cadaveric organ allografts (32 kidneys, 2 pancreases, and 2 livers), 26 kidneys are still supporting life, 3 after more than a year; the pancreases and livers are also functioning. 20 patients are not receiving steroids, and 15 of these have not had any additional immunosuppressive agents. In these patients infectious complications have not been severe, but a gastroduodenal lymphoma has developed in 1 patient. 6 patients were given 'Cytimum' (a cyclophosphamide derivative) and steroids in addition to cyclosporin A: 5 of these died of infections and 1 also had a lymphoma. 11 patients received additional steroids: 1 of these died from septicaemia and lymphoma. Nephrotoxicity can be avoided by perioperative hydration and forced diuresis. Cyclosporin A is effective on its own and is a very potent immunosuppressive drug. Additional immunosuppressive agents may lead to severe complications.

Variation in plasma prednisolone concentrations in renal transplant recipients given enteric-coated prednisolone

Renal transplant recipients receiving intermittent haemodialysis and kept under normal ward conditions showed appreciable differences in plasma prednisolone concentrations after therapeutic doses of enteric-coated prednisolone tablets. This gross day-to-day variation occurred irrespective of the dosage used. Breakfast given before prednisolone tended to reduce the rate of absorption of the drug, the effect being quantitatively most pronounced with large doses. Haemodialysis had no apparent effect on the elimination of prednisolone from plasma. Such erratic blood concentrations of prednisolone as observed in these patients, possibly resulting from variable absorption, may be potentially hazardous. Hence use of enteric-coated tablets in renal transplant recipients should be viewed with caution.

Loss of metacarpal and iliac bone in chronic renal failure: influence of haemodialysis, parathyroid activity, type of renal disease, physical activity and heparin consumption

1. Bone loss was assessed by measurement of cortical thickness of metacarpal bone by X-ray and of trabecular bone area in serial bone biopsies in 49 patients with chronic renal failure, six before and 45 during maintenance haemodialysis treatment.

2. Metacarpal cortical measurements (MCM) were very reproducible (coefficient of variation 1·95%), whereas bone area measurements by histology showed great variability. There was no correlation between rates of change of MCM and bone area over the same period, although both tended to fall with time.

3. The mean annual rate of bone loss measured by MCM for patients on dialysis was 2·08 ± 0·32 mm/year (mean ±1 sem) and this rate was not significantly different from the mean rate of loss of 2·49 ± 0·78 mm/year for the six patients who were not on maintenance haemodialysis. 61% of all patients showed a significant decrease during the period of study (1–6 years), but none had symptoms attributable to bone loss.

4. The loss tended to be greatest in women over the age of 40 years. The initial amount of bone and the rate of loss measured by MCM or bone histology were not influenced significantly by the presence or absence of histological or radiological evidence of parathyroid overactivity or of osteomalacia, nor by differences in the causes of renal disease.

5. Loss of metacarpal cortical bone correlated with heparin consumption during haemodialysis in men but not in women. The amount of bone and its rate of loss was not influenced by the presence of an arteriovenous shunt in one arm compared with the other. In neither sex did bone loss correlate with physical activity.

6. A relative deficiency of calcium due to a low dietary calcium intake and intestinal malabsorption of calcium, together with a dialysate calcium of only 1·5 mmol/l, may be more important causes of bone loss in patients in this study.

Treatment of renal bone disease with 1 alpha-hydroxylated derivatives of vitamin D3. Clinical, biochemical, radiographic and histological responses

Forty patients with severe bone disease and chronic renal failure were treated with 1 alpha-hydroxycholecalciferol (1 alpha-OHD3) or 1,25-dihydroxycholecalciferol (1,25(OH)2D3) for 7--49 months (total = 738 patient months). There were symptomatic, biochemical and radiographic improvements in the majority of patients (greater than 70 per cent). Paired bone biopsies, taken before and during treatment in 26 patients, showed no change in bone matrix area, whereas matrix area decreased in a control group of 26 patients over the same period. There were small but consistent decreases in bone marrow fibrosis and in bone cell (osteoblast and osteoclast) counts in treated patients but not in controls. However, the proportion of patients who showed histological 'cure', in the sense of complete reversal of marrow fibrosis or excess osteoid was no greater in the treated than in the control group...

Severe acidosis from acetazolamide in a diabetic patient

An insulin-dependent diabetic patient with nephropathy developed severe acidosis after treatment with acetazolamide for glaucoma. A renal tubular abnormality may have allowed the usually self-limiting acidosis of acetazolamide to progress. It is suggested that the plasma electrolytes of patients at risk should be monitored.

The position of the nutrient foramen in the growing tibia and femur of the rat

In rats of 40, 49 and 59 days of age the positions of the femoral and tibial nutrient foramina were determined by direct measurement, using a travelling microscope. The femoral nutrient foramen remained constant in position with increasing age, whereas the tibial nutrient foramen moved relatively nearer to the distal end of the shaft. In the case of the femur this can be accounted for entirely by differences in growth rates at the epiphyseal plates of the femur compensating for the disproportion in the distances of the foramen from the two plates. In the tibia, however, extension of the extremely oblique nutrient canal as the bone increases in girth is also involved. Bone remodelling in the vicinity of the canal is not necessary to explain the results.

Correlation of clinical, biochemical and skeletal responses to 1alpha-hydroxyvitamin D3 in renal bone disease

Thirty-five patients with bone disease and chronic renal failure (twenty-four on maintenance haemodialysis) were treated for 7--39 months with 1alpha-hydroxyvitamin D3, 2--2.5 microgram daily by mouth. Symptoms (bone pain and muscle weakness) and radiographic appearances improved and plasma alkaline phosphatase returned to normal in the majority of patients (87, 76 and 75% respectively). In contrast, histological appearances in bone improved in only 46% twenty-three patients from whom paired biopsies were available, and this change was not greatly different from that seen in a comparable group of untreated patients. Significant correlations were noted in individual patients between the changes in symptoms, X-rays, plasma alkaline phosphatase and immunoreactive parathyroid hormone and these, in turn, were related to histological changes in bone, although these latter changes were often small. It is concluded that 1alpha-hydroxyvitamin D3 is a useful new drug in the treatment of renal bone disease, but that the evaluation of the response depends critically on the method of assessment used.

Renal osteodystrophy in nondialysed adolescents. Long-term treatment with 1alpha-hydroxycholecalciferol

The effects of small oral doses (1-2 microgram/day) of 1alpha-hydroxycholecalciferol, given for 1 to 2 years, have been examined in four nondialysed adolescents with chronic renal failure and bone disease. Treatment increased calcium retention and plasma calcium, and decreased plasma levels of alkaline phosphatase, hydroxyproline, and immunoreactive parathyroid hormone. X-ray abnormalities of bone regressed, and 2 patients underwent successful surgical correction of knock-knees; bone histology in these 2 was normal at the time of operation. 2 patients developed hypercalcaemia which promptly reversed when 1alpha-hydroxycholecalciferol was withdrawn. In one patient treatment was initially successful, but later there was biochemical, radiographic, and histological evidence of relapse. Long-term treatment of such patients with 1alpha-hydroxycholecalciferol may be effective and facilitate the surgical correction of deformities, but this is not invariable. Toxic effects are similar to those of vitamin D itself, but are more readily reversible.

The effect of 1,25-dihydroxycholecalciferol on renal tubular reabsorption of phosphate, intestinal absorption of calcium and bone histology in hypophosphataemic renal tubular rickets

1. 1,25-Dihydroxycholecalciferol (1,25-(OH)2-D3) was given at a dose of 5-0 nmol (2-1 mug) daily by mouth for 4-12 days to three patients with hypophosphataemic (type I), vitamin D-resistant rickets. 2. 1,25-(OH)2-D3 increased intestinal absorption and urinary excretion of calcium without significant effect on the renal handling of phosphate or its plasma concentration. 3. It is concluded that in this type of vitamin D-resistant rickets the renal phosphate abnormality is unlikely to be due to diminished endogenous production of 1,25-(OH)2-D3. 4. The difference between this condition and other hypophosphataemic states is discussed.