Drug Reactions Flashcards
name risk factors for drug eruptions
- young adults > infants/elderly
- female
- concomitant disease eg viral infections, CF
- immune status
- drugs
- hapten forming
- high molecular weight
- beta lactam
- NSAIDs
hapten
- molecule that when bound to carrier molecule can elicit an immune response
- eg urushiol, the toxin found in poison ivy
which drugs cause gingival hyperplasia
calcium channel blockers
drug manifestations of co-trixomazole
- erythema nodosum, erythema multiforme, Stevens-Johnsons syndrome
causes of a maculopapular or exanthematous rash
- penicillin, cephalosporins, sulphonamide, anti-epileptics (carbamazepine)
Maculopapular or Exanthematous rash
- the most common type
- occurs 4-12 days after drug
- type IV hypersensitivity reaction
- Usually mild and self-limiting, but can progress to severe life-threatening reaction
- Presenting with generalised erythematous macule and papules with/out fever and eosinophilia
- Wide spread symmetrical rash
- Pruritus
name 6 indicators of a potenitally more severe reaction
- Involvement of mucous membranes and face (oedema and erythema)
- Widespread confluent erythema
- Fever (>38.5)
- Blisters, purpura and necrosis
- SOB, wheezing
- Lymphadenopathy and arthralgia
what does a maculopapular/exanthematous rash resemble
measles
what is a true allergy due to
immunological mechanism
urticarial rash
- usually due to true allergy or pseudoallergy
- characterise by wheals or angioedema
- associated with anaphylaxis
how quickly does an uritcarial rash come on
within the hour
wheals
- A wheal is a superficial skin-coloured or pale skin swelling, usually surrounded by erythema. Usually very itchy, may have a burning sensation
angioedema
- Angioedema is a deeper swelling within the skin or mucous membranes
true allergy
IgE mediated hypersensitivity reaction after re challenge with drug causes an urticarial reaction
- pencillin - 0.05%
pseudoallergy
- direct release of infalmmatory medaitors from mast cells on first exposure causes a urticarial reaction
- eg NSAIDs, opiates cause mast cell degranulation
- eg Penicillin and Cephalosporins trigger IgE responses
which drugs can cause acne
steroids, androgens
drugs inducing bullous pemphigoid
- ACE inhibitors, penicillin, furosemide
fixed drug eruption
- lesions occur in the same area every time a particular drug is taken - the number of sites involved may increase
- well demarcated red painful round/ovoid plaques
- may resolve with persistent pigmentation once the drug is stopped
which drugs can cause a fixed drug eruption
paracetamol, tetracycline, sulfonamide and aspirin
SJS and TEN
- SJS and TEN are believed to be variants of the same condition, distinct from erythema multiforme
- Rare, acute, serious and potentially fatal skin reaction in which there is sheet-like skin and mucosal loss
- Anyone on medication can develop it unpredictably.
which drugs are known to cause SJS/TEN
- NSAIDs, steroids, methotrexate, allopurinol, sulphonamides, co-trimoxazole, anti-convulsants and penicillins
what is the most common infectious cause of SJS/TEN
Mycoplasma pneumoniae
clinical features of SJS/TEN
- prodromal illness resembling URT infection
- Abrupt onset of tender/painful skin rash that spreads rapidly. Blisters merge to form sheets of skin detachment
- Nikolsky’s sign positive
- eyes: symbblepharon, conjunctivitis, anterior uveitis, corneal ulcers etc
side effects of phenytoin
an anti convulsant
- An antifolate drugs that can cause folate deficiency resulting in macrocytic anaemia. A symptom of this is tiredness
- Duputyren’s contracture
- Gingival hypertrophy
- Morbilliform rash/acne
- SJS/TEN
define adverse drug reaction
Defined as any undesirable reaction, whether expected, predictable or not that results in a detriment to the wellbeing of the patient in any way, whether symptomatic, detectable or not, in the absence of another biologically plausible explanation that can be proven.
type A drug reactions
A: Augmented pharmacological effects – dose dependent and predictable
diuretics cauing dehydration
type A reaction
ACEi/ARB causing d and v
type A reaction
name two causes of post renal failure
- Methysergide – used for migraine and cluster headaches. Causes retroperitoneal fibrosis
- Chemotherapy – used for acute leukaemias
type A reactions
type B reactions
B: Bizarre effects (or idiosyncratic) – dose independent and unpredictable
give 3 examples of type B reactions
- Drug rashes
- Chloramphenicol causes bone marrow aplasia
- Halothane (general anaesthetic) causes hepatic necrosis
type C reactions
chronic - due to prolonged therapy
give 3 examples of type C reactions
- Steroid therapy – Cushing’s disease
- Beta blockers can lead to diabetes through decrease in peripheral blood flow and altered insulin sensitivity
- This is why they ae not used much in young people with hypertension
- NSAIDs can lead to hypertension – see above
how can type C reactions be prevented
- emphasise the importance of monitoring - can be anticipated
- the patient must be warned before starting therapy
type D drug reaction
delayed - remote from treatment, often years after stopping
type D reactions - 2 examples
- Secondary malignancies post chemotherapy
- Craniofacial abnormalities in the children of women taking isotretinoin
type E reactions
end of treatment effect - can be due to abrupt withdrawal/rebound effects
steroid withdrawal can cause
Addisonian crisis - type E reaction
beta blocker withdrawal can cause
unstable angina in a pt with angina - type E
drug food interactions
what is a true penicillin allergy due to
- Allergy is due to a degradation product of the beta-lactams, true anaphylactic reactions only occur <0.05%
- Aztreonam is safe in penicillin type 1 allergy, it is a beta-lactam that is active against Gram negative bacteria.
