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PHAR 262 > Labelling Tc-99m Kits > Flashcards

Labelling Tc-99m Kits Flashcards

1
Q

RPs need to change their oxidation state in order to label a pharmaceutical component. t/f

A

true

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2
Q

what is oxidation?

A

the loss of electron(s)

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3
Q

what is reduction?

A

the gain of electron(s)

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4
Q

what are oxidizing agents?

A

substances that causes oxidation, therefore is reduced

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5
Q

what are reducing agents?

A

substances that causes reduction, therefore is oxidized

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6
Q

which RPs have the oxidation state of +7?

A

sodium pertechnetate and sulphur colloid

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7
Q

in order for Tc-99m to react with the pharm. as a foreign label, it must be ______ (reduced/oxidized). why?

A

reduced
- it’ll bring it to a more reactive state

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8
Q

what is the chemical behaviour “IN VIVO” of Tc-99m?

A

pertechnetate mimics I- (charge+size)
useful thyroid imaging agent

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9
Q

what is the chemical behaviour “IN VITRO” of Tc-99m?

A

when Tc-99m is in its more reactive state, it can label compounds by forming covalent, ionic, or coordinate covalent bones

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9
Q

what are the examples of technetium TAGGED compounds? (what does tagged compound mean?)

A

tagged = function is not dependent on Tc
examples: MDP, SC, MAA

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10
Q

what are the examples of technetium ESSENTIAL compounds? (what does essential compound mean?)

A

essential = Tc needed in the structure for RP to work
examples: HMPAO, MAG3, ECD, MIBI

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11
Q

what does lyophilized mean?

A

removal of all water

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12
Q

what are found in RP kits?

A

reducing (Sn - tin) + complexing agents

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13
Q

what may be contained in RP kits?

A

stabilizers, buffers, anti-oxidants, transfer ligands, inert atmospheres

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14
Q

what is the goal of the reducing agent in terms of Tc-99m?

A

to oxidize Tc-99m to get from oxidation state of +7 to something lower.

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15
Q

what is the most common reducing agent?

A

stannous chloride dihydrate
stannous = Sn2+

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16
Q

what is the amount of Tc added to kits?

A

~10^-9M

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17
Q

what is the amount of stannous Sn needed? what does it do?

A

0.1-1mg
needed to reduce the Tc

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18
Q

what is the ratio of tin to Tc-99m?

A

Sn:Tc-99m
10^6-9:1

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19
Q

why is the ratio between Sn to Tc-99m the way it is?

A
  • ensure rapid reduction of Tc-99m
  • inhibit the effects of radiolysis due to free radicals tending to act as oxidizing agents
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20
Q

what is the complexing agent?

A

the pharmaceutical

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21
Q

what are the common types of complexing agents?

A

a coordination/principle ligands, a chelating agent, or particles, proteins or antibodies

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22
Q

what are coordinate covalent bonds?

A

bonds that has one atom donating a lone pair of electrons to the bond

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23
Q

what is a ligand? what is it also known as?

A

the molecule that donates electron pair(s); pharm portion
aka chelating agent aka complexing agent

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24
Q

what are coordination numbers?

A

number of bonds between the ligand and the metal ion

25
Q

what is the coordination numbers for technetium?

A

~4 to 9

26
Q

what is a monodentate ligand?

A

molecule forming ONE coordinate covalent bond with the metal ion

27
Q

what is a polydentate ligand? what is it also called?

A

molecule forming SEVERAL bonds with the metal ion
aka chelating agent

28
Q

what is a chelate?

A

structure that involves a metal ion and a polydentate ligand/chelating agent

29
Q

what are the 2 reasons for excess complexing agents?

A
  1. ensure the reduced tech. atoms are complexed with the pharm (ex. high efficiency)
  2. complexes the access tin in the kit
30
Q

what happens to the reduced Tc that doesn’t complexed with the pharm?

A
  • oxidizes back to 7+ state
    or - react with water to hydrolyzed reduced tech (impurity)
31
Q

list these in the order of smallest to largest quantities.
reducing agent, complexing agent, Tc-99m

A

99m-Tc < reducing agent < complexing agent

32
Q

what are transfer ligands?

A

a weak ligand that is added to temporarily bind reduced tech during slow labelling reactions

33
Q

what are ancillary chelating agents?

A

takes over for complexing agents that don’t have affinity for Sn.

34
Q

what are adjuvants?

A

additional ingredients found in the kits

35
Q

what do stabilizers do for the kits?

A

maintains the integrity of the RP - keeps the RP in its intended state

36
Q

what are some examples of stabilizers?

A
  • bactericidal agents (benzyl alcohol, parabéns)
  • anti-oxidants (ascorbic acid, gentisic acid)
37
Q

what are anti-oxidants for in the kits?

A

to limit the effect of free radicals because they are more easily oxidized than other kit components

38
Q

what is radiochemical purity referring to?

A

% bound to the pharmaceutical

39
Q

what are the three chemical forms of Tc-99m found in the kits?

A
  1. bound tc-complex
  2. free pertechnetate
  3. hydrolyzed reduced
40
Q

describe bound tc-complex.

A

Tc is in its desired form and bound to the pharm.

41
Q

describe free pertechnetate. (TcO4-)

A

Tc that is NOT REDUCED or bound to the pharm.

42
Q

describe hydrolyzed reduced. (TcO2)

A

Reduced Tc but not bound to pharm.

43
Q

what are the notable exceptions for chelates?

A

MAA, SC, MIBI

44
Q

_____ (lower/higher) amount of bound Tc = better image quality.

A

higher

45
Q

%bound is also known as? which describes what?

A

%tag - describes the measure of radiochemical purity

46
Q

metal ions are soluble in ___ (high/low) pH and if ___ (bound/unbound) to a ligand.

A

low - acidic
bound to ligands

47
Q

TcO4- (free pert) tends to undergo hydrolysis. t/f

A

false
only Sn2+ and reduced Tc are concerns for hydrolysis

48
Q

describe free radicals.

A
  • result of indirect radiolysis
  • free radicals will break bones between radionuclides and complexing agents then act as oxidizing agents
49
Q

free radical formation is exaggerated in the presence of O2. t/f

A

true

50
Q

the number of free radicals increases with time. therefore making the older eluate having the higher amount of free radicals. t/f

A

true

51
Q

radiolysis is more common with ____ (high/low) activity and with ____ (high/low) energy radionuclides.

A

high activity and high energy radionuclides

52
Q

how are insoluble colloid particles formed?

A

when metal reacts with water (hydrolysis)

53
Q

why is carrier 99Tc bad?

A

if there is a high amount of carrier, it can use up too much of the other kit’s ingredients

54
Q

what are some characteristics of 99Tc?

A
  • amount of carrier increases with time
  • it builds up in the generator between elutions as well as in the vial after elution
55
Q

what kit component(s) is/are at risk of undergoing oxidation?

a) pertechnetate (TcO4-)
b) reduced Tc-99m
c) pertechnetate (TcO4-) and Sn2+
d) reduced Tc-99m and Sn2+

A

d) reduced Tc-99m and Sn2+

56
Q

what kit component(s) is/are at risk of undergoing hydrolysis?

a) pertechnetate (TcO4-)
b) reduced Tc-99m
c) pertechnetate (TcO4-) and Sn2+
d) reduced Tc-99m and Sn2+

A

d) reduced Tc-99m and Sn2+

57
Q

why is free pertechnetate an issue?

A

it causes non-target uptake (usually in thyroid and stomach)

58
Q

what causes free pertechnetate (TcO4-)?

A
  • oxidizing agents (O2 or free radicals) – oxidization of Sn2+ or reduced Tc
59
Q

what are some solutions to help with free pertechnetate?

A
  • use of excess stannous ions
  • avoid introducing o2
  • backfilling with nitrogen and argon
  • use of anti-oxidants
  • avoid using old eluate
60
Q

what forms when reduced 99mTc undergoes hydrolysis?

A

formation of insoluble colloid particles occur

61
Q

what occurs when Sn2+ undergoes hydrolysis?

A

formation of colloid that binds with reduced tech

PHAR 262 (12 decks)

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