drugs affecting calcium balance
TRANSCRIPT
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Calcium –Physiological Roles
Excitability of nerves and muscles and regulates permeability of cell membranes. Also integrity of cell menbanes
Ca++ essential for excitation and coupling of all types of muscles
Excitation and secretion of endocrine and exocrine glands and release of neurotransmitters from erve endings
Intracellular messenger for hormones, autacoids and transmitters
Impulse generation and conduction in heart
Coagulation of Blood
Structural function of Bone and Teeth - hydroxyapatite 2
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Plasma Calcium Level
Regulated by 3 hormones Parathormone, calcitonin and Calcitriol (active vit. D)
Normal plasma level = 9-11 mg/dl
40% is bound to plasma protein – albumin, 10% -citrate, carbonate and phosphate and 50% is free ionized and important form
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Circulating Calcium Ionized calcium (free calcium)
Responsible for calcium function
Can be directly measured
Hypoalbuminemia – total Ca++ may be low but conc. of Ca++ is usually normal
Acidosis – favours ionization
Alkalosis – disfavours ionization – hyperventilation precipitates tetany and laryngospasm in Calcium deficiency
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Pharmacokinetics Absorbed from entire small intestine including duodenum
– carrier mediated active transport under the influence of Vit.D
Phytates, phosphates, oxalates and tetracycline – reduces absorption
Glucocorticoides and Phenytoin reduces Ca absorption
Filtered through glomerulus but mostly reabsorbed
Vit. D increases and Calcitonin decreases reabsorption in proximal tuule
PTH increases distal tubular reabsorption
300 mg is excreted daily in urine and faeces
Daily requirement: 800 -1500 mg per day (1/3rd absorbed)
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Calcium Preparations
Calcium chloride (27% Ca): freely water soluble, but irritant - tissue necrosis on IM or IV (extravasation). Orally also irritant
Calcium gluconate (9 % Ca): 0.5 gm/1 gm tabs and 10% injections – non irritant (preferred)
Calcium lactate: orally non irritant
Calcium dibasic phosphate (23% Ca): Insoluble, but with HCl form soluble salts - antacids and replacement
Calcium chloride: Insoluble and no irritant – antacids
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Calcium - Uses1. Tetany: Severe cases Calcium gluconate 10 to 20 ml IV
over 10 minutes followed by 50 to 100 ml of Ca gluconate solution over 6 Hrs Oxygen inhalation, IV fluids then oral therapy
2. Dietary supplement: growing children, pregnant, lactating and meopausal etc. Also in men and women reduce the bone loss
3. Osteoporosis: Prevention ant treatment of osteoporosis with HRT/raloxifene/Alendronate – to ensure Ca++ deficiency does not occur Calcium and Vit. D3 used as adjuvant
4. Empirically in dermatoses, parathesia and weakness
5. Antacids
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Vitamin D Mainly D3 (cholecalciferol) and D2 (calciferol)
Both are equally active in man
Calcitriol (active form of D3) is more important physiologically
Released from liver in blood and binds to specific vit D binding globulin
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VITAMIN D SYNTHESIS
SKIN LIVER KIDNEY
7-DEHYDROCHOLESTEROL
VITAMIN D3
VITAMIN D3
25(OH)VITAMIN D
h25-HYDROXYLASE
25(OH)VITAMIN D
1,25(OH)2 VITAMIN D
(ACTIVE METABOLITE)
1a-HYDROXYLASE
TISSUE-SPECIFIC VITAMIN D RESPONSES11
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Vitamin D
The body can supply its own Vitamin D via the synthetic pathways
Alternatively, Vitamin D may be supplied by Vitamin D - enriched foods. The classic examples are milk and multiple vitamins.
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Actions of calcitriol Enhancement of absorption of Ca and PO4 from
intestine
By increasing the synthesis of calcium channels and a carrier “calcium binding protein (CaBP)” or calbindin
Analogous to stroid hormones – binds to cytoplasmic vit D receptor (VDR)-translocation-increased synthesis of mRNA-regulation of protein synthesis
But, why quick? - Activation of VDR also promotes endocytotic capture of Calcium and transport across the duodenal mucosa
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Calcitriol also enhances recruitment and differentiation of osteoclast precursor for remodelling – resorption of Calcium and PO4 from bone
Mature osteoclasts lack VDR, induces “receptor for acivaton of nuclear factor-kB-ligand (RAANKL)” in osteoblasts and activates osteoclasts indirectly
Laying down and mineralization of osteoids
Also enhances tubular reabsorption of Calcium
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VITAMIN D MECHANISM OF ACTION
5’ UNTRANSLATED REGION VITAMIN D RESPONSIVE GENE
TRANSCRIPTION START SITE
RNA POLVIT D / VDR
IN THE NUCLEUS
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Pharmacokinetics Absorbed fro intestine in presence of Bile salts mainly
by lymphatics
D3 is better absorbed than D2
Binds to alpha-globulin and stored in fatty tissues for many months
Half life varies from 1 – 18 days
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Unitage and preparation
1mcg of Cholecalciferol = 40 IU of vit.D
Calciferol (D2): oily solutions in gelatin capsules –25000/50000 IU caps
Cholecalciferol (D3): oral and IM injections –given 3 to 4 weeks intervals
Calcitriol: 0.25 to 1 mcg orally on altenate days
Alfacalcidol: Prodrug – rapidly hydrolysed to calcitriol in liver. Equally active to calitriol on long term use. Dose – 1-2 mcg/day
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Vit D - Uses Prophylaxis (400 IU/day ) and treatment(3000 -4000
IU/day) of rickets & osteomalacia : alternatively Oral/IM injection 3-6 lac IU every 2-6
month interval
Metabolic Rickets Vit D resistant rickets: PO4 with high doses of calcitriol
Vit D dependent rickets
Renal rickets
Senile or postmenopausal osteoporosis
Hypoparathyroidism: calcitriol/alfacalcitriol
Fanconi like syndrome Calcipotriol : Vitamin D analog used topically in psoriasis
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Vitamin D deficiency
•Deficiency of vitamin D leads to:
Rickets in small children.
Osteoporosis
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Clinical manifestation
1. Osseous changes:
1) Head: craniotabes, frontal bossing, box like skull, delayed closure of anterior fontanelle
2) Teeth: delayed eruption, with abnormal order
3) Chest: rachitic rosary, pigeon chest, funnel-shaped chest
4) Spinal column: scoliosis,kyphosis, and lordosis
5) Extremities: bowlegs
6) Rachitic dwarfism
2. Muscular system: potbelly, late in standing and walking
3. Motor development: delayed
4. Other nervous and mental symptoms
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Treatment
1. Food and nursing care
2. Prevention of complications
3. Special therapy
1) Vitamin D therapy
A. General method
Vitamin D 2000-4000IU/day for 2-4 weeks, then
change to preventive dosage (400IU).
B. A single large dose:
For severe case, or Rickets with complication, or those who
can’t bear oral therapy. Vitamin D3 3 LAC -6 LAC IU, im,
preventive dosage can be used after 2-6 months.
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Prevention1. pregnant and lactating women should take
adequate amount of vitamin D.
2. Advocate sunbathing
3.Advocate breast feeding, give supplementary food on time
4. Vitamin D supplementation:
• In prematures, twins & weak babies: 800 IU/day
• For term babies and infants : 400 IU per day,
• For those babies who can’t maintain a daily supplementation: Vitamin D3 1L-2L IU IM.
5. Calcium supplementation: 24
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Vitamin D - Sources• Sunlight is the most
important source
• Not found naturally in many foods
• Synthesized in body
• Plants (ergosterol)– Sun-cured forages
• Fluid milk products are fortified with vitamin D
• Oily fish & Fish liver oil
• Egg yolk
• Butter
• Liver
• Difficult for vegetarians25
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TOXICITY
•Hypervitaminosis Dcauses hypercalcemia, which manifest as:
• Nausea & vomiting• Excessive thirst , polyuria & anorexia • Severe itching• Joint & muscle pains• Disorientation & coma.• Calcification of soft tissue
– Lungs, heart, blood vessels ,
• Hypercalcemia– Normal is ~ 10 mg/dl– Excess blood calcium leads to stone formation in
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Parathyroid Hormone Location : Posterior to thyroid gland , 4 in nos
Secreted by principal cells
Preproparathyroid hormone proparathyroidhormone PTH(84 AA polypeptide)
Hypocalcemia is a principal factor regulating PTH synthesis & release, mediated through activation of adenylate cyclase & subsequent increase in cAMP level
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Rapidly metabolised in liver & kidney
T1/2 is 2-5 min
Actions Bone
Kidney
Intestine
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PTH receptor G protein coupled receptor on activation increases cAMP formation & intracellular Ca++ in target cells, in bone target cells are osteoblast
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PTH,
Calcium &
Phosphate
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CALCIUM, PTH, AND VITAMIN D FEEDBACK LOOPS
NORMAL BLOOD Ca
RISING BLOOD Ca
FALLING BLOOD Ca
SUPPRESS PTH
STIMULATE PTH
BONE RESORPTION
URINARY LOSS
1,25(OH)2 D PRODUCTION
BONE RESORPTION
URINARY LOSS
1,25(OH)2 D PRODUCTION31
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Calcitonin
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Calcitonin, peptide hormone secreted by thethyroid gland, tends to decrease plasma Caconcentration and, in general, has effectsopposite to those of PTH
Parafollicular cells, or C cells, lying in theinterstitial fluid between the follicles of thethyroid gland
32-amino acid peptide with a molecular weight ofabout 3400
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The primary stimulus for calcitoninsecretion is increased plasma Ca ionconcentration
calcitonin decreases blood Ca ionconcentration rapidly, within minutesafter injection of the calcitonin
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Inhibit bone resorption by direct action on Osteoclasts
Also inhibits the proximal tubular reabsorption of calcium and phosphate by direct action on kidney
Action is mediated through G- protein coupled calcitonin receptor & increased cAMP formation but target cells are different from that of PTH
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Calcitonin : Preparations Porcine (Natural) calcitonin:
Antigenic
Synthetic salmon calcitonin:
More potent due to slower metabolism
Synthetic human calcitonin:
1 IU = 4 μg of std preparation
Calcitonin is given by SC/IM routes. Salmon calcitonin is also available as nasal spray
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• Hypercalcemia states (e.g associated with neoplasia)
• Pagets disease of bone:
• Postmenopausal osteoporosis & corticosteroid induced osteoporosis:
• Salmon calcitonin is used as nasal spray along with Vit D supplements 200 IU /day
Uses
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Bisphophonates (BPNs)
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Introduction Non-hormonal agent in Ca++ homeostasis
Recently attracted considerable attention
Prevent osteoporosis and useful in metabolic bone diseases and hypercalcaemia
Most effective “antiresorptive” drug at present
BPNs are analogous of pyrophosphates – Carbon atom replacing “P-O-P skeleton”
BPNs have selective affinity for Calcium phosphate –so calcified tissues
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Bisphosphonates have two side
chains:
R1 affects binding affinity to
bone;
R2 affects antiresorptive capacity
and, possibly,Side-effect profile.
Bisphosphonates vary in potency
Based on these specific side
chains.
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Generations of Bisphosphonates With each successive generation, there has been
increased potency, with more selectivity for inhibition of resorption and less inhibition of bone formation.
First-generation bisphosphonates, such as etidronateand clodronate, inhibit bone formation and bone resorption equally.
Second-generation bisphosphonates include pamidronate and alendronate
The third generation includes the highly potent risedronate and zolendronate.
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BPNs - MOA BPNs have selective affinity for Calcium phosphate – so calcified
tissues
2 main component of Bone – Bone matrix and Solid mineral phase (hydroxyapatite)
• Normally, The non-mineralized osteoid covers the mineralized bone matrix preventing its resorption by osteoclasts
• For resorption – osteoids must get dissolved or mineralized (solubilized) such that osteoclasts can attach to the mineralized matrix
• In resorptive pits – acidic zone is created at ruffled boarders of osteoclasts followed by resorption of matrix by acid hydrolases
• BPNs localize in the acidic zone due to high affinity for Ca++ ions
• Ca++ ions released from bone surface due to high acidity BPNs also released – internalized into osteoclasts by endocytosis
• Results in
Accelerated apoptosis of osteoclasts reducing their number
Disruption of the cytoskeleton of the ruffled boarder of osteoclasts42
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Therapeutic Uses1. Osteoporosis: Alendronate>HRT or raloxifene
I. Prevention and treatment of post-manaupasal osteoporosis
II. Both Men and Women – age related, steroid induced and idiopathic osteoporosis
Oestrogen prevents only vertebral fracture, BNPs 5 years protection
2. Pagets disease: Honeycomb like bone architecture – arrest osteolytic lesions, reduce bone pain and improve secondary symptoms. Alendronate, Risedronate, Pami and Zole are used. Calcitonin combination better
3. Hypercalcaemia of Malignancy: Medical emergency with altered consciousness – Pamidronate 60-90 mg IV 2-4 hours or Zoledronate 4 mg IV 15 minutes. Suplement with calcitonin IM 6-12 Hrly for 2 days
4. Osteolytic Bone Metastasis
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Individual Drugs1. Etidronate: Not used anymore
2. Pamidronate: Only IV 60-90 mg for 2-4 Hrs, weekly or monthly in Pagets disease and hypercalcaemia
3. Alendronate: Available in oral form 5, 10, 35, 70 mg tabs. Prevention of osteoporosis in man and woman.
a. In empty stomach with glass of water
b. Do not allow to lie down or eat till 30 minutes –oesophagitis; Tea, coffee, mineral water, Juice, NSAIDs
c. ADRs: Gastric errosion, retrosternal pain, flatulence
d. Bioavailability 1%, 50% goes to Bone, terminal elimination half-life 10.5 years
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Individual Drugs – contd.4. Risedronate: Similar to Alendronate, but more
potent
• Used in osteoporosis and Paget`s disease
5. Zolendronate: Prenterally effective, highly potent
• Suppression of osteoclastic activity and additional antitumor effect (mevalonate pathway)
• Proliferation of bony metastasis of Prostate and breast cancer cells are suppressed
• Can be infused in 15 minutes
• ADR: Flu-like symptoms due to cytokine release
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Adverse effects Oral bisphosphonates causes Gastrointestinal
complications such as gastritis or esophagitis, abdominal pain, nausea, vomiting, diarrhea, and constipation.
To minimize gastrointestinal inflammation
And ulcer, patients should remain upright (sitting or standing) for at least 30 minutes after taking the medication
Bisphosphonate-related osteonecrosis of the jaw Phossy jaw
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Osteoporosis
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A systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture.
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Primary osteoporosis Postmenopausal
↓ estrogen results in ↑ osteoclastic activity without ↑osteoblastic activity
Bone loss – 2-3% per year of total bone mass
Most common fx: vertebral, distal forearm
Age related – 3rd decade of life starts slow decline in bone mass at rate
of 0.5-1% per year
Most common types of fx: hip and radius, F>M
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Secondary OsteoporosisDisease states
Acromegaly
Addison’s disease
Amyloidosis
Anorexia
COPD
Hemochromatosis
Hyperparathyroidism
Lymphoma and leukemia
Malabsorption states
Multiple myeloma
Multiple sclerosis
Rheumatoid arthritis
Sarcoidosis
Severe liver dz, esp. PBC
Thalessemia
Thyrotoxicosis
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Drugs causing osteoporosis Aluminum
Anticonvulsants
Excessive thyroxine
Glucocorticoids
GnRH agonists
Heparin
Lithium
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Normal Bone Remodeling: A Balance of Bone Resorption and Formation
2–4 weeks 3–4 months
Resting Stage
Formation RemodelingCompleted
Activation Resorption
Lining cells
Osteoclastprecursors
OsteoclastsOsteoblasts
Bone remodeling unit
Lining cells
FormationResorption
Secondary mineralization
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Osteoporosis: Resorption Exceeds Formation
2–4 weeks 3–4 months
Lining cells
Osteoclast precursors
Bone remodeling unit
1. Adapted from: Rosen CJ. Available at: http://www.endotext.org/parathyroid/index.htm. Accessed December 7,2007.
Lining cells
OsteoclastsOsteoblasts
FormationResorption
Pits develop that weaken bone
Resting Stage Formation Remodeling
CompletedActivation Resorption Secondary
Mineralization
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Treatment Objectives
Osteoclast
Inhibition of resorption
Osteoblast
Stimulation of formation55
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Osteoporosis drugs used
Anabolic Agent Antiresorptive Agents
Function Forms new bone Suppresses bone resorption
Mechanism ↑s osteoblast activity ↓ osteoclast activity
Bone turnover
Accelerates turnover Slows turnover
BMD effect Forms new bone ↑ bone volume
↑ mineralization of existing bone
Drugs Teriparatide , Fluoride, Androgens
BisphosphonatesCalcitonin , ERT,SERMs, Calcium,VitD ,Thiazides
Dual action bone agent :Strontium ranelate56
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Bisphosphonates
Etidronate
Pamidronate
Alendronate
Risedronate
Ibandronate
Tiludronate
Zoledronate
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Bisphosphonates
Advantages
Increases BMD by 1-4%, decreases fracture risk by 41-44%
No increased risk of breast, uterine ca or thromboembolic events
Weekly dosing
Disadvantages
Risk of gastrointestinal sx
ex dosing instructions
Contraindicated in ESRD; need to adjust dose according to creatinine clearance
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Estrogen Replacement Therapy (ERT)
Indication: Used to prevent and treat osteoporosis (FDA indication is for prevention)
Mechanism:↓es osteoclast activity,
Acts on osteoblast to ↓ production of IL- 6
↑ production of osteoprotegerin,there by interfering with recruitment of osteoclast precursors.
Dose: Estrogen: 0.625mg od, Progesterone 2.5mg qd (if uterus present)
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ERT
Advantages
Increases bone density (1-5%) and decreases risk of fracture (25%)
Relief of hot flashes, vaginal dryness
Decreases LDL, increases HDL
?Prevention of Alzheimer’s disease
Relatively inexpensive
Disadvantages ↑ bone loss after stopping
↑ risk of uterine ca
↑ risk of thromboembolicevents
Possible ↑ risk of breast cancer
Side effects: breast tenderness,
breakthrough bleeding
↑ risk of coronary events in women with known CAD in first year of use (HERS trial)
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Selective Estrogen Receptor Modulators (SERMs)
1.Raloxifene: partial agonist in bone and CVS but an antagonist in endometriumand breast. 2.Tamoxifen: antagonist in breast carcinoma cells, blood vessels but agonist in uterus, bone, liver and pitutary
Dose: Raloxifene 60mg od
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SERMS
Advantages
Increases bone density (2%) and decreases fracture risk (30%)
No stimulation of breast or endometrial tissue
No need for progestin in women with uterus
Decrease LDL
Disadvantages
Increased risk of thromboembolic events
Doesn’t treat post-menopausal sx
May increase hot flashes
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Vitamin D
It may improve intestinal calcium absorption ,suppress bone remodeling and improve BMD in individuals with marginal or deficient Vit D status.
Calcitriol – suppresses the PTH function and reduce bone turnover.
Dosage: 400-800 IU /day.
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Thiazide diuretics
Reduce urinary calcium excretion and constrain bone loss in patients with hypercalciuria.
Dosage :
Hydrochlorothiazide – 25 mg once or twice daily.
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Bone forming agents
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rParathyroid hormone [rPTH(1-34), teriparatide]
Mechanism of action:
Stimulates new bone formation on trabecular and cortical bone surfaces by preferential stimulation of osteoblastic activity over osteoclastic activity.
Daily SC injections of 40mcg of rPTH for 12-18 months , increased BMD by 9-13% and decreased risk of vertebral fractures by 65 to 69 %
Side effects: Occasional headache and nausea
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Strontium ranelate Oral strontium ranelate is an alternative oral treatment,
belonging to a class of drugs called "dual action bone agents" (DABAs).
Proven efficacy, especially in the prevention of vertebral fracture.
Mechanism of action: ↑collagen & noncollagen protein systhesis, enhances preosteoblast differentiation, ↓osteoclast function
Dosage : 2 g oral suspension daily Adverse effects : thromboembolism
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Glucocorticoid-Induced Osteoporosis: Treatment
Only bisphosphonates have been demonstrated in large clinical trials to reduce the risk of fractures in patients being treated with glucocorticoids.
Risedronate prevents bone loss and reduces vertebral fracture risk by ~70%. Similar beneficial effects are observed in studies of alendronate.
Controlled trials of hormone therapy have shown bone-sparing effects, and calcitonin also has some protective effect in the spine.
Thiazides reduce urine calcium loss, but their role in prevention of fractures is unclear.
PTH has also been studied in a small group of women with glucocorticoid-induced osteoporosis, where bone mass increased substantially, and teriparatide is currently being investigated in a larger multicenter trial.
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Investigational Agents Ospemifene, Lasofoxifene
Bazedoxifene
Arzoxifene
Strontium ranelate
Increases collagen & noncollagen protein synthesis, enhances preosteoblastdifferentiation, reduces osteoclast function
Denosumab
Human mAb, inhibits RANKL which inhibits osteoclast activation and survival
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A human monoclonal antibody to the receptor activator of NFkBligand (RANKL), which is given subcutaneously once every sixmonthsOral calciomimetic drugs that stimulate intermittent production of parathyroid hormoneSelective oestrogen receptor modulators with mixed oestrogenicand anti-oestrogenic effectsInhibitors of sclerostin, a protein produced by bone that is a negative regulator of bone formation, and its signalling pathway
Investigation of the causes and management of poor compliance and persistence
Assessment of the long term effectsof anti-resorptive treatments on bone strength
Ongoing research
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Thank you
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