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Basic Science > Drugs acting on bone metabolism > Flashcards

Drugs acting on bone metabolism Flashcards

1
Q

Describe what happens in bone remodelling?

A
  • Cycle commences with Osteoclast RECRUITMENT by CYTOKINES e.g.IL-6
  • OC adhere to trabecular bone, dig cowslip lacunae by secreting Hydrogen ions and proteolytic enzymes
  • > LIBERATION of factors embedded in bone e.g. insulin like growth factor
  • ISGF -> activate OB which have been primed to develop into precursor cells by parathyroid hormone and 1,25 dihydroxycholecalciferol
  • OB invade pits , synethise and secrete OSTEOID, the organic matrix of bone
  • the OSTEOID is then mineralised i.e. complex calcium phosphate crystals (hydroxyapatite) are deposited.
  • OB and precursors secrete IGF-1 and IL-6 which become embedded in the bone and recruit OC.
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2
Q

What type of drug are BISPHOSONATES?

A
  • A class of drug characterised by a P-C-P BACKBONE RESISTANCE TO PHOSPHATASES
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3
Q

Can you draw the chemical formulae for bisphosphonates?

A

OH R1 OH

  I                 I                 I

O= P————-C————–P ===O

   |                  |                |

 OH             R<sub>2 </sub>             OH
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4
Q

What secures the longevity of the bisphosphonates when given?

A
  • The fact that nothing can metabolise the P-C-P backbone
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5
Q

How do bisphosphonates act?

A
  • By DIRECTLY STABILIZING THE HYDROXYAPATITE CRYSTAL -> making it MORE RESISTANT TO RESORPTION
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6
Q

What is important about AMINOBISPHOSPHONATES?

Can you name some?

A
  • They have MORE SPECIFIC OSTEOCLASTIC ACTIVITY than early bisphosphonates such as etidronate.
  • examples include- PAMIDRONATE, ALENDRONATE
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7
Q

How do AMINOBISPHOSPHONATES act? What does this do?

A
  • By DIRECTLY INHIBITING THE ACTION OF OSTEOCLASTS via the Mevalonate pathway inhibiting FARNESYL PYROPHOSPHATE SYNTHASE. -> PREVENTS PRENYLATION ( formation of the brush border) and FUNCTIONING of SIGNALLING PROTEINS required for OC formation
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8
Q

How are bisphosphonates given?

A
  • Orally ( poorly absorbed) or parentally
  • 50% of dose accumulates at sites of bone mineralisation, where it remains until bone is absorbed
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9
Q

What is the use of bisphosphonates?

A
  • tx POSTMENOPAUSE and GLUCORTICOID induced OSTEOPOROSIS
  • PAGET’S DISEASE
  • MALIGNANT HYPERCALCAEMIA
  • OSTEOGENESIS IMPERFECTA
  • FIBROUS DYSPLASIA
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10
Q

What are the adverse effects of bisphosphonates?

A
  • 1)ORAL intake must be on an EMPTY STOMACH-> GASTRIC PAIN and OESPHAGITIS
  • 2) TRANSIENT LEUCOPENIA
  • 3) SCLERITIS
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11
Q

What are vitamin D analogue used for?

A
  • metabolic bone disease
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12
Q

Name some vitamin D derivatives ?

A
  • Vitamin D3 - CHOLECALCIFEROL
    • formed in skin from dehydrocholesterol by UV light
  • Vitamin D2- Ergocalciferol( calciferol)
    • formed in plants by UV radiation.
    • used to tx rickets, osteomalacia, and vit d deficiency
  • 25 -OH- vitamin D3- aka calciferol
    • main storage form of vitamin D
  • 1,25-OH- vitamin D3- aka calcitrol
    • most potent metabolite in regulating plasma calcium. used to tx renal osteodystrophy
  • 1alpha -OH- cholecalciferol- aka alfocalcidol-
    • synthetic derivative of vitamin D3
    • undergoes hepatic25- hydroxylation to calciferol.
    • used to tx renal osteodystrophy ( increased calcitriol)
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13
Q

what are the side effects of vitamin D Dervivatives?

A
  • Xs intake -> HYPERCALCAEMIA
  • Increased requirements for vitamin D if on anti convulsive medication - e.g. Phenytoin
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14
Q

What is Calcitonin?

A
  • calcitonin is a 32 amino acid peptide
  • secreted by the PARAFOLLICULAR C CELLS of the thyroid gland
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15
Q

When is calcitonin secreted ? When is it inhibited?

A
  • In response to ELEVATED SERUM CALCIUM
  • Inhibited by DECREASED SERUM CALCIUM
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16
Q

What is Calcitonin’s function?

A
  • Directs INHIBITS OSTEOCLASTS -> DECREASE in CALCIUM
17
Q

What preparations can the calcitonin derivates come in ?

A
  • natural - porcine = calcitonin
  • synthetic- salmon-= salcalcitonin
18
Q

How is calcitonin given?

A
  • subcutanously
  • im injection
  • intranasally
19
Q

What are calcitonin’s clinical use?

A
  • First line for PAGET’S disease to reduce pain and reduce neurologically complications
  • MALIGNANT HYPERCALCAEMIA
  • **POST MENOPAUSE **
  • GLUCOCORTICAL INDUCED OSTEOPOROSIS
20
Q

What are calcitonin’s side effects?

A
  • Nausea and Vomiting
  • Facial flushing
  • Tingling sensation in the hands
  • Unpleasant taste in the mouth
  • Increased risk of stress fractures
21
Q

What is PARATHYROID HORMONE? example ?

A
  • Is an ANABOLIC agent used in the treatment of OSTEOPOROSIS Tetriparatide ( PTH)
22
Q

How can PTH be given?

A
  • the 1-34 portion of the 84 amino-acid- peptide can be given by subcutaneous injection
23
Q

What is the anabolic effect of PTH?

A
  • INCREASED BONE FORMATION
  • IMPROVED MICROARCHITECTURE of bone
24
Q

What does Tetriparatide work on?

A
  • the periosteal surface of bone, but it also causes endosteal resorption,
  • INCREASING the diameter of bone and it BENDING & TORSIONAL STRENGTH BY INCREASING THEIR 2nd and POLAR MOMENTS OF INERTIA
25
Q

What also does PTH activate?

A
  • Bone lining cells and osteoblasts partially if intermittent stimulation is used
  • Osteoclasts are stimulated with continuous stimulation by teriparatide
26
Q

What are the concerns with Tetriparatide?

A
  • increased osteosarcoma in rats
  • subtrochanteric femoral fractures
  • leg cramps
  • dizziness
27
Q

What is Strontium?

A
  • group 2 , period 5 element, with atomic no 38
  • similar to calcium
28
Q

Where does it have a clinical role?

A
  • In early tx of osteoporosis. given orally
29
Q

What are its effects ?

A
  • INCREASE BONE FORMATION- anabolic effect
  • DECREASE BONE RESORPTION- anticatabolic effect

Basic Science (31 decks)

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