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aa BDS M6 - Therapeutics > 1. Antibiotics - Penicillins > Flashcards

1. Antibiotics - Penicillins Flashcards

1
Q

What must we know about different drugs?

A
  1. drug name
  2. drug class
  3. mechanism of action
  4. relevant pharmacology
  5. indication(s)
  6. contraindication(s)
  7. known side effects
  8. adverse reactions
  9. interactions
  10. clinical application
  11. doses
  12. alternatives
  13. common clinical scenario
  14. clinical application
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2
Q

What class of drug is amoxicillin?

A

aminopenicillin

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3
Q

What class of drug is penicillin ?

A

Beta-Lactam

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4
Q

What is the mode of action of penicillin?

A
  • interferes with cell wall synthesis
    • cell wall synthesis inhibitors
      • cephalosporins
      • carbapenums
      • monobactams
  • bactericidal
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5
Q

What is the mechanism of action of penicillin?

A
  1. Inhibits cross linking peptides
    • inhibits transpeptidase/penicillin binding protein
  2. inactivates autolysin inhibitors
  3. kill rapidly dividing organisms because of these mechanisms
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6
Q

What is the spectrum of activity of penicillin? What bacteria can it target?

A

narrow spectrum
- most gram +ve cocci
- gram +ve bacilli
- some gram -ve cocci
- Strep A, B, C, G, bovus and pneumoniae
- anaerobic potential
- fusobact spp
- clostridium
- anaerobic strep

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7
Q

What bacterias is penicillin most effective against?

A

aerobic gram +ve cocci

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8
Q

What are the kill characteristics of penicillin?

A

time dependent killing mechanism
- act preferentially on rapidly dividing bacteria
- takes time for the inhibition process and eventual microorganism rupture
- consistently high blood levels of the penicillin are needed

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9
Q

What are some of the common penicillin preparations?

A
  • Penicillin G (Benzylpenicillin)
  • Pencillin V (Phenoxymethylpenicillin)
  • Procaine/Benzathine Penicillin (Procaine Benzylpenicillin, Benzathine Benzylpenicillin)
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10
Q

What are the key features of penicillin G?

A
  • Injectable form of penicillin
  • rarely if ever used orally
  • gastric acid labile
  • low absorption
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11
Q

What are the key features of penicillin V?

A
  • well absorbed
  • gastric acid stable
  • suitable for oral administration
  • spectrum of activity similar to pen G but slightly less active
  • slow absorption/can have variable plasma concentrations following absorption
  • regarded as highly effective against dento-alveolar infections
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12
Q

What are the key features of procaine/benzathine penicillin?

A
  • intramuscular forms used as a depo injection
  • primarily given as slow release prolonged use
  • tendency to be used for long term prophylaxis in some individuals and for the treatment of early or late latent syphilis
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13
Q

What is the oral absorption % of benzylpenicillin (G), and of phenoxymethylpenicillin (V)?

A

benzylpenicillin (G) - 20%

phenoxymethylpenicillin (V) - 60-73%

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14
Q

What are the half lives of benzylpenicillin (G) and phenoxymethylpenicillin (V) after oral absorption?

A

benzylpenicillin (G) - 30 mins

phenoxymethylpenicillin (V) - 30-45mins

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15
Q

What are the peak serum levels of benzylpenicillin (G) and phenoxymethylpenicillin (V) after oral absorption?

A

benzylpenicillin (G) - 2um/mL

phenoxymethylpenicillin (V) - 4ug/mL

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16
Q

What are the peak serum times of benzylpenicillin (G) and
phenoxymethylpenicillin (V) after oral absorption?

A

30-60mins for both

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17
Q

What are the NPB serum levels of benzylpenicllin (G) and phenoxymethylpenicillin (V) after oral absorption?

A

benzylpenicllin (G) - 0.9ug/mL

phenoxymethylpenicillin (V) - 0.8ug/mL

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18
Q

What is the protein binding % of benzylpenicllin (G) and phenoxymethylpenicillin (V) after oral absorption?

A

benzylpenicllin (G) - 45-68%

phenoxymethylpenicillin (V) - 75-89%

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19
Q

Do benzylpenicllin (G) and phenoxymethylpenicillin (V) have food affect?

A

benzylpenicllin (G) - yes

phenoxymethylpenicillin (V) - no

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20
Q

Why is penicillin G usually reserved for severe infections?

A

it has rapid peak plasma concentrations following IV administration

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21
Q

What are some indications for penicillin G IV use?

A
  • severe infections
  • oral route compromise (malabsorption syndrome or vomiting)
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22
Q

What type of bacteria should you be aware of before prescribing penicillins?

A

beware Beta Lactamase producing bacteria

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23
Q

How common is penicillin hypersensitivity?

A

8% of population have some sort of hypersensitivity

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24
Q

What percentage of the population have an allergic reaction during any course of an antiobiotic?

A

4%

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25
Q

What are the most common types of reactions to penicillin?

A

maculopapular or urticarial rash

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26
Q

What percentage of anaphylactic fatalities does pencillin account for (in the US)?

A

~75%

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27
Q

What age range are penicillin reactions most likely in?

A

20-49

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28
Q

What group of people are penicillin fatalities most likely in?

A

fatal reactions more likely in elderly due to reduced cardiopulmonary function

29
Q

Of immediate reactions to penicillin, what percentage of these result in anaphylaxis?

A

0.004% to 0.015%

30
Q

How many in 10,000 penicillin courses does anaphylaxis occur in?

A

1-5 per 10,000

31
Q

How common is fatality as a result of immediate reaction to penicillin?

A

1:60,000 courses

32
Q

Within what time frame do more severe reactions to penicillin occur?

A

96% in the first 60 mins

33
Q

What percentage of the population is estimated to eventually have an allergic reaction to penicillin at some point?

A

eventually 1-10% of population

34
Q

What occurs during an immediate reaction to penicillin?

A

mast cell degranulation and histamine release

35
Q

What are the symptoms of an immediate reaction to penicillin?

A
  • nausea/vomiting
  • pruritis
  • erythema/urticaria/rash
  • wheeze
  • laryngeal oedema
  • angiodema
  • bronchospasm
  • hypotension
  • cardiovascular collapse
36
Q

What rashes may present from a delayed reaction to penicillin?

A
  • vesticular
  • maculo-papular
  • bullous
  • urticarial
  • scarlatiniform
37
Q

What are delayed reactions (type II) mediated by?

A

mediated by IgG or IgM

38
Q

What can delayed reactions (type II) cause?

A
  • blood dyscrasias
  • haemolytic anaemia
  • leukopenia
  • thrombocytopenia
  • aplastic anaemia
39
Q

What other obscure autoimmune reactions may occur to penicillin?

A
  • eosinophilia
  • Stevens-Johnson syndrome
  • exfoliative dermatitis
  • DRESS syndrome
  • Toxic Epidermal Necrolysis (TEN)
40
Q

What may Toxic Epidermal Necrolysis be considered a form of?

A

one of the most severe forms of Stevens-Johnson syndrome

41
Q

What does DRESS syndrome stand for?

A

Drug Reaction with Eosinophilia and Systemic Symptoms

42
Q

What may DRESS syndrome result in?

A
  • rash
  • fever
  • inflammation of internal organs with lymphadenopathy and characteristic haematological abnormalities
    • eosinophilia, thrombocytopenia, atypical lymphocytosis
43
Q

What is the approximate mortality rate of DRESS syndrome?

A

approx. 10%

44
Q

What are risk factors for penicillin hypersensitivity?

A
  • multiple drug allergies
  • atopic disease
  • asthma
  • allergic rhinitis
  • nasal polyps
45
Q

What percentage of those with a history of a true penicillin allergy will demonstrate an allergy on re-exposure?

A

15-40%

4-6 times greater likelihood of subsequent reaction than those with a negative history

46
Q

Why should you avoid giving a course of penicillin to someone who’s had one recently?

A

serum IgE antibodies often retained 10-1000 days, more likely to have a hypersensitivity reaction

re-exposure and risk of recurrent allergy is high in those with repeated exposure short term or those with long IgE expression

47
Q

What must you do if an adverse drug reaction (ADR) occurs?

A

complete the YellowCard reporting mechanism

48
Q

Who is the YellowCard ADR reporting scheme administered by?

A

Medicines and Healthcare products Regulatory Agency (MHRA)

49
Q

What can be reported using the YellowCard reporting system?

A
  1. side effects (also knows as ADRs)
  2. medical device adverse incidents
  3. defective medicines
  4. counterfeit or fake medicines or medical devices
  5. safety concerns for e-cigarettes or their refill containers (e-liquids)
50
Q

What is the dose, interval, duration and route of penicillin V?

A

dose: 250-500mg
interval: 6 hourly
duration: 3-5 days
route: oral

51
Q

What is the dose, interval, duration, and route of penicillin G?

A

dose: 1.2g
interval: 6 hourly
duration: 3-5 days
route: IV

52
Q

Is it better to fast or have food when taking penicillin V?

A

Better to fast - take dose 30 mins before food or 2 hours after

53
Q

Is a loading dose used for penicillin V?

A

it can be used, may be useful in rapid or severe infections

54
Q

What are the 3 main mechanisms of bacteria evasion of penicillin?

A
  1. reduced drug binding to Penicllin binding protein PBD (altering configuration)
  2. hydrolysis of the drug by beta lactamase enzymes (this is the principle mechanism in most species)
  3. development of a tolerance by disabling their autolysis mechanism (penicillin becomes bacteriostatic instead of bacteriocidal)
55
Q

What are some of the most common interactions with penicillin?

A

antagonism (bacteriostatic)
- NSAID/probenecid
- warfarin?
- methotrexate
- oral contraceptive

56
Q

What does an antagonism interaction mean?

A

the administration of 2 drugs together results in neither of them working effectively

57
Q

What does NSAID interaction with penicillin result in?

A

can increase the serum half life by decreasing renal excretion, causing increased plasma concentrations

58
Q

Why is there a potential/theoretical interaction between broad spectrum antiobiotics and warfarin?

A

broad spectrum antibiotics may cause an alteration in INR

59
Q

What is the interaction of methodtrexate and penicillin?

A

penicillin can reduce the excretion of methotrexate via the tubules in the kidneys, this can eventually lead to toxicity

60
Q

What is the theoretical interaction of the oral contraceptive and penicillin?

A

penicillin theoretically reduce the contraceptive effect of eostrogens, no definitive evidence

61
Q

What are some of the common unwanted effects of pencillin?

A
  • diarrhoea
  • nausea
  • skin rash
62
Q

What are some of the uncommon unwanted effects of penicillin?

A
  • vomiting
  • urticaria and pruritis
  • arthralgia
63
Q

What are some of the very rare unwanted effects of penicillin?

A
  • mucocutaneous candidiasis
  • hypersensitivity reactions
    • rash
    • anaphylaxis
    • TENS, DRESS etc
  • toxicity particularly in severe renal failure
  • hepatoxicity
  • diarrhoea/colitis
  • black hairy tongue
  • neutro/leucocytes/thrombocytopenia
  • increased PT/INR/bleeding
64
Q

As an unwanted effect to penicillin, through what mechanisms can increased PT/INR/bleeding occur?

A
  • bone marrow suppression
  • immunologic platelet destruction
  • inhibition platelet function
  • potentiation warfarin
  • interruption vit K factors
65
Q

What are some of the less common unwanted effects of penicillin?

A
  • fast or irregular breathing
  • shortness of breath
  • fever
  • arthralgia
  • lightheaded or fainting (sudden)
  • swelling around the face
  • red, scaly skin
  • skiing rash, hives, itching
66
Q

What are some of the rare unwanted effects of penicillin?

A
  • abdominal or stomach cramps and pain (severe)
  • abdominal tenderness
  • convulsions (seizures)
  • oliguria
  • diarrhoea (watery and severe), which may also be bloody
  • mental depression
  • nausea and vomiting
  • sore throat and fever
  • bleeding or bruising
  • yellow eyes or skin
67
Q

What are some possible alternatives to use instead of penicillin?

A

metronidazole, clarithromycin, erythromycin, clindamycin (+ clavulanate)

68
Q

How are penicillin cleared from the body?

A

renal clearance

69
Q

Summary slide (penicillin):

A

aa BDS M6 - Therapeutics (6 decks)

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