Effect of phenobarbitone treatment on vitamin D metabolism in mammals

Effects of chronic administration of zonisamide, an antiepileptic drug, on bone mineral density and their prevention with alfacalcidol in growing rats

We investigated the effects of chronic administration of zonisamide, an antiepileptic agent, on bone metabolism in growing rats. Administration of zonisamide at a dose of 80 mg/kg per day, s.c. for 5 weeks significantly decreased bone mineral density (BMD) at the tibial metaphysis and the diaphysis. The percent rate of decrease in BMD at the tibial metaphysis and the tibial diaphysis was 9.2% and 5.0%, respectively. There was no significant difference between these groups in the growth of the rats. Treatment with zonisamide at a dose of 80 mg/kg increased serum pyridinoline level, a marker of bone resorption, while it does not affect the serum intact osteocalcin level, a marker of bone formation. Combined administration of alfacalcidol, an active vitamin D(3) metabolite, at a dose of 0.1 microg/kg per day with zonisamide prevented a decrease in BMD and showed an increase of serum pyridinoline levels. These results suggest that zonisamide may cause bone loss by accelerating bone resorption rather than inhibiting bone formation. Moreover, the bone loss induced by zonisamide could be prevented by combining zonisamide with alfacalcidol.

Phenytoin and fluoride act in concert to stimulate bone formation and to increase bone volume in adult male rats

We have recently demonstrated that phenytoin is an osteogenic agent at low doses. The present paper describes observations that a mitogenic dose (i.e., 20 microM in BGJb medium) of fluoride significantly augments the phenytoin-dependent stimulation of normal human bone cell proliferation and alkaline phosphatase (ALP) activity in cell culture. Additionally, the present study was designed to investigate whether fluoride and phenytoin would interact to increase bone formation in rats in vivo. Four groups of weight-matched adult male rats received daily I.P. injection of (1) vehicle (10% DMSO), (2) 5 mg/kg/day phenytoin, (3) 5 mg/kg/day phenytoin and 50 ppm NaF, and (4) 50 ppm NaF and vehicle, respectively, for 36 days. Sodium fluoride (NaF) was delivered in drinking water. Blood samples were drawn weekly and analyzed for serum osteocalcin, ALP, calcium, phosphorus, and 25(OH)D3. Rats were labeled with tetracycline at day 21 and 30 and histomorphometric analysis was carried out on the tibia at the end of the experiment. Neither agent by itself or together affected the serum calcium, phosphorus, or 25(OH)D3 levels. All measures of bone formation, i.e., serum osteocalcin level and ALP activity, bone ALP specific activity, mineral apposition rate, bone formation rate, and % bone formation surface, were increased by each agent. Fluoride and phenytoin together produced bigger increases in each parameter than did each agent alone. Trabecular bone volume was increased in the tibial metaphysis by fluoride or phenytoin alone; and when administered together, the two agents produced a greater increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Osteomalacia should be sought and treated before withdrawal of anticonvulsant therapy in UK Asians

Individuals from the Asian sub-continent in the United Kingdom are at particular risk of developing osteomalacia. We report a Gujarati woman who developed osteomalacia whilst taking anticonvulsant drugs; withdrawal of anticonvulsant therapy was followed by a seizure complicated by femoral neck fracture. In patients with other risk factors for osteomalacia, as is the case for Asians living in Britain, anticonvulsant drugs should not be reduced or withdrawn until osteomalacia, which puts the skeleton at increased risk of fracture, and its associated hypocalcaemia, which reduces seizure threshold, have been sought and adequately treated.

Decreased bone density in severely handicapped children and adults, with reference to the influence of limited mobility and anticonvulsant medication

Bone density and related biochemical parameters were investigated in institutionalised children and adults with severe handicaps, who were classified according to the degree of limited mobility (group 1, bed-ridden; group 2, capable of crawling; group 3, capable of walking) and according to whether or not they were receiving anticonvulsants. As determined by microdensitometric analysis of radiograms of the second metacarpal bone, bone width (D), bone pattern area (sigma GS) and bone salt density (sigma GS/D) were decreased in the patients, the decreases being most prominent in group 1, followed by groups 2 and 3, in that order. Significant decreases of sigma GS and sigma GS/D, but not of D, were found in patients on anticonvulsant treatment in comparison to patients without therapy. Serum alkaline phosphatase (Al-p) and parathyroid hormone (iPTH) as well as urinary calcium and cyclic adenosine-3',5'-monophosphate (cAMP) excretion were significantly increased in group 1. In comparison to patients without therapy, anticonvulsant-treated children showed significantly decreased levels of serum calcium (Ca), ionised Ca (Ca2+), 25-hydroxy vitamin D3 and urinary phosphate (PO4) excretion, and elevated levels of Al-p, iPTH and calcitonin (iCT). It is suggested that limited physical activity results in a mild hyperparathyroid state, which is aggravated in patients on anticonvulsant treatment.

Do anticonvulsant drugs commonly induce osteomalacia?

Twenty adult epileptic out-patients who had received anticonvulsant therapy for a mean duration of 15 years were assessed for clinical, biochemical, radioisotopic and bone biopsy evidence of osteomalacia. Occasional biochemical abnormalities were demonstrated but no individual subject was found to have osteomalacia. There is increasing evidence to cast doubt on the existence of a strong relationship between anticonvulsant drugs and osteomalacia. This evidence is reviewed and it is concluded that in the presence of adequate sunlight exposure anticonvulsant therapy alone is most unlikely to lead to osteomalacia in adults.

Privational and malabsorption metabolic bone disease: plasma vitamin D metabolite concentrations and their relationship to quantitative bone histology

Plasma 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 25-hydroxyvitamin D (25OHD) concentrations were measured in twenty patients with metabolic bone disease due either to privational causes (10 patients) or malabsorption (10 patients). Abnormally low plasma 1,25(OH)2D3 levels were found in eleven patients, six with privational and five with malabsorption bone disease. Normal plasma 1,25(OH)2D3 concentrations were found in the remaining nine patients; of these, five were either receiving anticonvulsant therapy or had been hospitalised prior to investigation. In the absence of either of these factors, normal plasma 1,25(OH)2D3 levels were only found in patients with malabsorption-associated bone disease. Plasma 25OHD levels were below normal in eleven patients; six had malabsorption and five had privational bone disease. In the fifteen patients not receiving anticonvulsants there were significant inverse correlations between plasma 1,25(OH)2D3 levels and the osteoid volume, surface and seam thickness index. This study indicates that plasma 1,25(OH)2D3 concentrations are low in privational osteomalacia in the absence of anticonvulsant therapy or hospitalisation, although normal levels may occur in malabsorption metabolic bone disease uncomplicated by these factors. The plasma 1,25(OH)2D3 concentration appears to be inversely related to the histological severity of bone disease in patients not receiving anticonvulsant therapy.

Influence of phenobarbital and diphenylhydantoin on the healing of rickets in the rat

Male weanling Sprague-Dawley rats were administered phenobarbital or diphenylhydantoin (phenytoin, dilantin, DPH), or a combination of the two drugs, while receiving a high calcium, low phosphorus vitamin D-deficient diet. A Line Test evaluation for calcification of the distal end of the radius was performed to determine the presence of rickets and the healing of the disease. After a period of 16 days, rickets had developed in a uniform manner in all groups regardless of drug treatment. Four I.U. of vitamin D3 were then administered to each animal and they were sacrificed either 3 or 9 days later. Three days after the administration of D3, bone calcification had started in all groups, with the greatest response being observed in the control group. Nine days after D3 administration, bone calcification was clearly impaired in PB and PB-DPH treated animals and slightly impaired in the DPH treated group when compared to controls. Weight gain was also impaired after PB and combined PB-DPH treatments. Based on these observations, it is suggested that anticonvulsant drugs, and in particular PB, inhibit, in a yet undetermined fashion, the normal calcification of the growth cartilage which accompanies a single physiological dose of cholecalciferol in the rat.

1,25-dihydroxycholecalciferol in renal osteodystrophy. Epiphysiolysis--anticonvulsant therapy

Three children with azotaemic renal osteodystrophy were treated with 1,25-dihydroxycholecalciferol (1,25(OH)2D3). All showed clinical, biochemical, and radiological improvement within 6 months of starting treatment. There were no complications. The dose of 1,25(OH)2D3 required was 0-5 microgram per day for 2 children aged 22 and 30 months, and 2 microgram per day for a 15-year-old boy. 2 of the patients were receiving phenobarbitone and phenytoin and in one of them prior treatment with dihydrotachysterol 0-5 mg daily and 6 microgram 1alpha-hydroxycholecalciferol (1alphaOHD3) daily had failed to induce improvement. In one patient, in whom serial iliac bone samples were available, 2 microgram 1,25(OH)2D3 resulted in histological improvement in previously severe osteomalacia. 1,25(OH)2D3 appears to be an effective and safe drug in the treatment of uraemic osteodystrophy.

Bone complications of anticonvulsants

Anticonculsant drug-induced disorders in mineral and bone metabolism are apparently quite common. Current evidence indicates that these drugs derange bone metabolism, both through induction of increased hepatic catabolism of vitamin D and its biologically active products, as well as by direct effects on membrane cation transport systems. The significant clinical manifestions of the disorder include rickets with defective bone development, decreased bone mass with increased risk of pathological fracture and reductions in serum calcium levels which may predispose to increased seizure frequency. There is a broad range of clinical presentation with a number of factors -- drug dose, duration of therapy, vitamin D intake, amount of sunlight exposure, degree of physical activity and presence of other concurrent diseases -- which appear to determine the severity of the clinical manifestations. Current evidence indicates that appropriate vitamin D and calcium supplementation can significantly reduce the clinical manifestations of this disorder. All patients receiving chronic anticonvulsant drug therapy should be carefully evaluted for the presence of drug-induced osteomalacia and treated appropriately with vitamin D. This is especially important in those patients in whom the presence of multiple risk factors indicates an increased likelihood of deranged mineral metabolism.