antihistamines

Question 1

define ADR

Answer 1

response to a drug that is noxious, unintended and occurs at normal doses and when appropriately

Question 2

difference between adverse drug event and adverse effect

Answer 2

ADE- injury resulting from medication
eg: wrong medication, penumonia

AE- side effect
eg N,V,D or allergic reaction

Question 3

who is predisposed to ADRs

Answer 3

elderly/children
chronic medical conditions
renal/hepatic impairment
previous history of ADR
poly pharmacy more than 5 meds
genetics

Question 4

classifications of ADRs

Answer 4

type A- augumented
85-90% of all ADRS
eg- side effect/drug interaction

type B- bizarre
10-15%
eg- hypersensitivity to drug (4 classifications)
eg: type 1,2,3,4 / allergy, genetics, intolerence

Question 5

Hypersenitivity classification

Answer 5

type 1 (immedite)
IgE-mediated - allergies, asthma, anaphylaxis

type 2 (antibody-mediated cytotoxic)
IgG/ IgM antibodies - blood group incompatibility

type 3 (immune complex-mediated)
IgG antibody inflammation- RA, systemic lupus, erhythematosus, etc

type 4 (T cell mediated)
delayed hypersensitivity/cytotoxic reactions in tissues - infections, contact dermatitis

Question 6

whats involved in type 1 hypersensitivity

Answer 6

IgE secreted and complexes with allergen
binds to mast cells and basophils
cell produces prostaglandins and leukotrienes
granules fuse with cell membrane to release substances like histamine and serotonin

Question 7

management plan for prescribing to penicillin allergy
1. n,v,d
2. skin rash
3. localised/mild itchy rash
4. severe skin reactions/liver injury
5. anaphylaxis, hypotension, collapse, swelling of airway, wholebody rash

Answer 7

1. side effects not allergy
2. (T-CELL- delayed reaction) avoid penicillin and prescribe cephalosporin
3. (IgE- mediated - immediate) “
4. (T-CELL- delayeD) avoid both and use non beta lactam antibiotics
5. (IgE mediated- immediate) “

Question 8

questions to ask about allergic reactions

Answer 8

1. nature of the reaction- how long did it happen after taking it?
2. when did it happen (more or less than 10 years ago)?
3. have they taken it again since?
4. how was it managed?

Question 9

penicillin allergy

Answer 9

50% of people will no longer be allergic in 5 years after reaction

it can be
1. severe or non severe depending on symptoms
2. immediate or delayed reaction after consumption

Question 10

examples of severe immediate penicillin allergy reaction

Answer 10

anaphylaxis, swelling of airway, hypotension, collapse

Question 11

examples of non severe immediate reaction

Answer 11

hives

Question 12

examples of delayed severe reaction

Answer 12

severe skin reactions with systemic symptoms or organ involvement

Question 13

examples of non severe delayed reactions

Answer 13

rash

Question 14

people with a penicillin allergy alsoallergic to cephalosporin?

Answer 14

1-2% of patients with penicillin allergy also have a cephalosporin allergy- should be fine

Question 15

diabetic foot infection with a delayed nonsevere reaction to penicillin (rash), prescribe

Answer 15

cefalexin

unless the reaction involved amoxicillin or ampicillin

Question 16

diabetic foot infection with delayed non servere to amox/amp, immediate nonsevere or severe or delayed severe penicillin allergy, prescribe

Answer 16

clindamycin

Question 17

histamine actions

Answer 17

bronchoconstriction
erythema
swelling
pain/itch
endothelial cell contraction
vasodilation
sensory nerve stimulation

Question 18

antihistamines MOA

Answer 18

reduce effects of histamine by binding to the H1 receptor and stabilising it in its inactive form

Question 19

clinical indications for antihistamines

Answer 19

-allergy (but asthma/anaphylactic)
-itching
-naeusea/vomiting
-motion sickness
-insomnia

Question 20

1st generation antihistamines

Answer 20

1st- sedating by crossing BBB blocking CNS histamine neurons and other receptors other than h1
Good for: allergic conditions, itch, nausea, vomiting
contraindication in: epileptic, elderly, parkinsons, children under 2

Question 21

2nd gen antihistamines

Answer 21

dont cross blood brain barrier and are less sedating as a result

indicated in: allergic rhinitis and chronic hives

Question 22

what to consider with antihistamines

Answer 22

indications (sedation required?)
side effects
absorption - capsule faster than tablet
approved in children/pregnancy
price

Question 23

define anaphylaxis

Answer 23

exposure to an allergen (food, insect or medicine) which results in a medical emergency due to the extent of symptoms

Question 24

first line treatment for anaphylaxis

Answer 24

adrenaline

Question 25

signs and symptoms of anaphylaxis

Answer 25

swelling of throat, tongue, face, lips, eyes
difficulty breathing/talking
wheezing/coughing
hives or welts
collpase/dizziness
vomiting/pain - insect allergy
pale/floppy-children