3. Hypersensitivity refers to undesirable reactions produced
by the normal immune system, including allergies
and autoimmunity.
These reactions may be damaging, uncomfortable, or
occasionally fatal.
Hypersensitivity reactions require a pre-sensitized
(immune) state of the host.
6. It is an immunologically mediated reaction producing
symptoms unrelated to the pharmacodynamic profile of the
drug, generally occuring with much smaller doses and have
a different time course of onset and duration.
Drug hypersensitivity reactions account for about 1/6th of all
adverse drug reactions.
Drug hypersensitivity reactions can become manifest in a
great variety of clinical symptoms and diseases, some of
which are quite severe and even fatal.
7. The most common allergic reactions occur in the skin and
are observed in 2-3% of hospitalized patients.
Antibiotics and antiepileptics are the drugs most frequently
causing them.
The risk of sensitization and the severity of clinical
symptoms depend on the state of immune activation of the
individual, the dose and duration of treatment, sex and the
immunogenetic predisposition.
8.
9. Type Mechanism Example
I IgE mediated hypersensitivty Anaphylaxis, urticaria,
asthma
II Cytotoxic, antibody dependent Hemolytic anaemia,
thrombocytopenia,
interstitial nephritis
III Immune complex damage Serum sickness, arthus
reaction, PSGN, SLE
IV Delayed or cellular
hypersensitivity
Contact dermatitis
transplant rejections
11. The IgE system is geared to react to small amounts of
antigens.
Very small amounts of a drug are apparently sufficient to
interact and stimulate these receptor-bound IgE molecules.
The drug causes formation of tissue sensitizing IgE
antibodies that are fixed to mast cells or leucocytes.
The subsequent exposure to drug, degranulates mast cells or
activates leucocytes with release of chemical mediators of
allergy.
12. IgE-mediated reactions to drugs are usually thought to
depend on the prior development of an immune response to a
hapten/carrier complex.
This sensitization phase is asymptomatic and may have
occurred during an earlier drug treatment.
These reactions include anaphylaxis, atopy and asthma.
13.
14. Clinical features
IgE-mediated reactions can cause mild to severe, even lethal,
diseases.
Symptoms may start with palmar, plantar, genital, and axillar
itch, and facial and thoracal redness
They often herald a severe, anaphylactic reaction, developing
rapidly within minutes.
Anaphylactic shock occurs often within 10 to 15 minutes, and
asphyxia due to laryngeal edema often occurs between 15 and
60 minutes.
15.
16. It rely on the formation of complement-fixing IgG
antibodies.
The mediator of type II reactions is IgG/ IgM, complement
or membrane attack complex.
It results when drug binds to RBC and is recognized by IgG
antibody.
The antigen antibody reaction then triggers the lysis of RBC
either by activating the complement system or by the action
of cytotoxic T cells or by phagocytosis by macrophages.
17. It is rare and best documented for high-dose penicillin and
cephalosporin.
Quinine-induced immune thrombocytopenia
It is caused by a remarkable class of IgG and/or IgM
immunoglobulins.
They react with selected epitopes on platelet membrane
glycoproteins, only when the drug is present in its soluble form.
Hemolytic anemia attributed to penicillin and its derivatives,
cephalosporins, levodopa, methyldopa, quinidine and some
antiinflammatory drugs is also a type II reaction to these drugs
18.
19. Soluble antigen antibody forms soluble complexes which
are deposited on vascular endothelium and activate
complement
This occurs within 1-2 weeks of drug administration
It is characterized by allergic inflammatory reactions in
tissues, glomerular nephritis and serum sickness.
Formation of immune complexes is a common event in the
frame of a normal immune response and does not normally
cause symptoms.
20. Immune complexes may be formed during drug treatment :
either if the drug forms a hapten-carrier complex and thus
gives rise to an immune reaction,
or if the drug is a (partly) foreign protein, which elicits an
immune reaction itself (e.g. a chimeric antibody).
21.
22. Clinical features
The clinical symptoms of a type III reaction may be
hypersensitivity, small vessel vasculitis and/or serum
sickness
Serum sickness was first described with the use of
heterologous or foreign serum for passive immunizations
Hypersensitivity vasculitis reportedly has an incidence of 10–
30 cases per million people per year.
Most reports concern cefaclor, followed by trimethoprim-
sulfamethoxazole, cephalexin, amoxicillin, NSAIDs and
diuretics.
23.
24.
25. These reactions are mediated by T cells and monocytes/
macrophages rather than by antibodies.
The activation of sensitized T cells results in the release of
cytokines which activate macrophages, granulocytes and
natural killer cells
The term delayed is used to differentiate a secondary cellular
response, which appears 48-72 hours after antigen exposure,
from an immediate hypersensitivity response.
Often mentioned disorders are contact dermatitis, chronic
transplant rejections and hypersensitivity pneumonitis
26.
27. They are a pathogenetically poorly defined problem
Most of these reactions resemble the clinical features of
milder forms of immediate, IgE-mediated reactions, but
some reactions cause anaphylaxis and can be lethal.
Detection of specific immune mechanism is negative.
NSAID induced pseudoallergic reactions seem to arise less
rapidly often >15 minutes after intake than true IgE-
mediated allergies
They may require higher drug doses than true IgE-mediated
reactions
28. Neither IgE nor Tcell reactions are evident.
The reactions are recurrent, but provocation tests often
remain negative.
The most common form of such reactions is related to
NSAIDs.
29.
30. Drug reactions commonly manifest
with dermatologic symptoms
The most common dermatologic
manifestation of drug reaction are
morbilliform rashes.
Urticaria is typically a
manifestation of a truly allergic,
Type I reaction, but it may appear
with Type III or pseudoallergic
reactions as well.
31. Severe nonallergic, hypersensitivity cutaneous reactions
include erythema multiforme, Stevens-Johnson syndrome,
and toxic epidermal necrolysis.
Eczematous rashes are most commonly associated with
topical medications and usually represent contact dermatitis,
which is classified as Type IV reaction to a drug exposure.
32.
33. Anaphylaxis is a serious allergic reaction that is rapid in
onset and may cause death.
Anaphylaxis typically presents many different symptoms over
minutes or hours with an average onset of 5 to 30 minutes if
exposure is intravenous and 2 hours for foods.
The most common areas affected include
skin, respiratory, gastrointestinal, heart and vasculature and
central nervous system with usually two or more being
involved.
34.
35.
36. Treatment for anaphylaxis
Immediate treatment with adrenaline is imperative.
Adrenaline 0.5 mg im is given. It is to be repeated every 5-10
min in case patient doesn’t improve.
H1 antihistaminic chlorpeniramine 20 mg im/slow iv acts as
an adjuvant.
Intravenous hydrocortisone sodium succinate 200 mg should
be added in severe/recurrent cases.
It may be followed by oral prednisolone for 3 days.
37. Anaphylactoid reactions refer to clinically similar events as
anaphylaxis but are not mediated by IgE.
It is also known as pseudoanaphylaxis.
They are a type of anaphylaxis that does not involve an
allergic reaction but are due to direct mast
cell degranulation.
40. Multivalency
Generally, an antigen must be presented to the immune
system in a multivalent form to elicit a specific immune
response.
Valency refers to the number of binding sites available to
bind antibody.
Multivalency is necessary to ensure cross-linking of
receptors on the surface of cells, which then causes
transduction of the signal within the cell and the initiation of
an immune response.
41. Drugs alone are poor stimulators of immune responses due
to their simple structure and low molecular weight.
Drugs can fulfill the requirement for multivalency and elicit
an immune response in two ways:
(1) Form hapten-carrier complexes and
(2) Be converted into reactive intermediates.
42. Haptenization
A hapten would be a particular drug, which would be
immunogenic in protein-conjugated but not free form.
An example would be penicillins and other betalactams that
bind covalently to proteins.
43. Conversion into reactive intermediates
This may occur via drug metabolism in the liver or
elsewhere.
This is the case with sulfonamides, which are acetylated
and oxidated to yield the predominant N4-sulfonamidoyl
hapten.
44. Chronic diseases that require continuous or frequent courses of
therapy with the same or cross-reactive drugs
Some allergic reactions are more likely to occur with certain
infections
Aminopenicillins with EBV infection,
Sulfonamides with AIDS patients
Atopy, a genetically determined state of hypersensitivity,
manifested as asthma, hay fever, and atopic dermatitis
History of other drug allergy
45.
46. The diagnosis of drug hypersensitivity is usually based on
clinical judgment, because definitive, confirmatory drug-
specific testing is often difficult.
General criteria for drug hypersensitivity
The patient’s symptomatology is consistent with an
immunologic reaction.
The patient was administered a drug known to cause such
symptoms.
47. The temporal sequence of drug administration and
appearance of symptoms is consistent with drug reaction.
Laboratory data are supportive of an immunologic
mechanism to explain the drug reaction.
48. Lab tests for IgE mediated
reactions
Skin testing
RAST testing
Serum Tryptase
49. Lab tests done for type II cytolytic reactions
50. Lab tests for type III immune complex reactions include
ESR
CRP
ANA
AHA
Complement studies
Tissue immunofluroscence studies
51. Lab tests for type IV
hypersensitivity reaction
Patch test
Lymphocyte proliferation assay
52. The most important and effective measure is the
discontinuation of the offending medication.
Alternative medications with unrelated chemical structures
should be substituted when available.
In the majority of patients, symptoms will resolve within two
weeks if the diagnosis of drug hypersensitivity is correct
53. Additional therapy for drug hypersensitivity reactions is
supportive and symptomatic.
Systemic corticosteroids may speed recovery in severe cases.
Topical corticosteroids and oral antihistamines may improve
dermatologic symptoms.
The severe drug reactions of Stevens-Johnson syndrome and
toxic epidermal necrolysis require additional intensive
therapy.
54. Desensitization is a method to reduce or eliminate an
organism's negative reaction to a substance or stimulus.
It is the loss of responsiveness to the continuing or
increasing dose of a drug
Desensitization is a reversible process that is dependent on
the continued presence of the drug.
It is also drug-dose dependent in that a substantial dose
increase may result in breakthrough allergic symptoms.
55. The starting dose for the drug can be determined by
performing intradermal skin tests with the native drug at a
dose that does not cause a non-specific irritant reaction.
For example, if a 0.02 ml intradermal injection of a drug at
1 mg/ml concentration does not cause a local or systemic
reaction, oral desensitization may be started at the dose
injected
Parenteral desensitization should be using 1/10 or 1/100 of
the dose that was administered intradermally.
57. All forms of natural and semisynthetic penicillins can cause
allergy, but it is more commonly seen after parenteral than oral
administration.
The reported history of penicillin allergy ranges from 1% to
10%.
Anaphylaxis is rare i.e 1 to 4 per 10,000 patients but may be
fatal.
It has been estimated that up to 60% of penicillin-allergic
patients will experience another allergic event if given the drug
again
58. There are two clinical pictures of penicillin allergy, acute
and sub-acute reactions mediated by IgE and IgG antibodies
respectively.
The acute allergic reaction arises immediately or rapidly
within minutes to an hour or two and includes sudden
anaphylaxis.
Sub acute picture may occur 7 to 10 days after penicillin
treatment starts or 1–2 days after repeat therapy. In this
setting the picture is sub-acute and can include urticaria,
fever and arthralgias or arthritis.
59. Major and Minor Determinants
The betalactam ring is unstable and readily acylates lysine
residues in proteins.
The penicilloyl epitope is produced, which is called the
“major determinant”
Penicilloyl IgE responses are associated with urticarial
reactions.
Beta lactams also haptenize covalently through carboxyl
and thiol groups, which results in a variety of “minor”
determinants.
Minor determinant IgE responses are associated with
anaphylaxis
60. Penicillin skin sensitivity testing
A positive skin test indicates the presence of IgE antibodies
to penicillin and immediately excludes the use of it and
related ß-lactam antibiotics
A BPO-polylysine conjugate and penicillin G in a
concentration of 1000U/ml are available for skin testing
It is performed by prick technique-a drop of a dilute
allergenic extract is placed on the skin, which is then pricked
or punctured through the extract, usually by “tenting” up
the skin with the tip of a stylet.
61. Hypersensitivity reactions are the most important adverse
effects of cephalosporins.
Rashes are the most frequent manifestation.
Anaphylactic reactions to cephalosporins are much less
common than anaphylaxis associated with penicillin
About 10% patients allergic to penicillin show cross
reactivity with cephalosporins.
62. Skin testing
Currently there are no reliable cephalosporin allergens
available for skin testing.
A positive Coomb’s test occurs in many patients, but
hemolysis is rare
Allergic reactions to cephalosporins do not appear to
correlate with positive penicillin test reactions.
63. Co-trimoxazole is used extensively in the HIV population for
prophylaxis against Pneumocystis carinii pneumonia.
The overall prevalence of sulfa hypersensitivity in the general
population is approximately 3.3%, while in the HIV population
it is in the range of 17-20%
The incidence of adverse events to cotrimazole is greater than
50% in patients receiving the medication for treatment for
active PCP
64. Sulfa drugs are metabolized in the liver by two pathways:
--oxidative metabolism by the cytochrome p450 system
- acetylation by N-acetyltransferase.
Sulfamethoxazole is predominantly cleared by acetylation
and excreted by active tubular excretion.
The alternative pathway yields a reactive metabolite,
sulfamethoxazole hydroxylamine, which can generate an
immune response
65. Mechanism
The mechanism of hypersensitivity to cotrimoxazole is poorly
understood.
Several hypotheses have been put forward to explain the
predominance of reactions in HIV patients:
◦ slow acetylation in HIV patients
◦ polypharmacy with drugs such as INH and rifampin that
compete for metabolism in the liver
◦ reduced availability of cellular glutathione
66. Hypersensitivity diseases caused by NSAIDs are relatively
common in the population
The prevalence of these reactions in the population varies
between 0.1% and 0.3%
Immunologic reactions to NSAIDs can be subdivided into
immediate and delayed.
Immediate Reactions
Urticaria and Angioedema - acetaminophen, and aspirin
68. Nonallergic Hypersensitivity
It includes Aspirin-induced asthma which is characterized by
asthma, rhinosinusitis, nasal polyposis, and aspirin
hypersensitivity.
Asthmatic reactions induced by NSAIDs occur in 5% to 20%
of adult asthmatic patients.
The pathogenesis seems to involve the combined effects of
chronic inflammation and a pharmacogenetic abnormality
of arachidonic acid metabolism in response to NSAIDs.
69.
70. This reaction typically occurs 7 to 10 days after exposure and
causes fever, arthralgias, and rash.
Mechanism involves drug-antibody complexes and complement
activation.
Some patients have frank arthritis, edema, or GI symptoms.
Symptoms are self-limited, lasting 1 to 2 wk.
β-lactam and sulfonamide antibiotics, iron dextran and
carbamazepine are mostly implicated.
Serum Sickness
71.
72. This disorder may develop when a drug alters the RBC
membrane, uncovering an antigen that induces autoantibody
production.
Antibodies then develop against the red blood cells. The
antibodies attach to red blood cells and cause them to break
down too early.
Drugs that can cause this type of hemolytic anemia include:
Cephalosporins, Dapsone, Levodopa, Levofloxacin,
Methyldopa, Nitrofurantoin , Quinidine
Hemolytic Anaemia
73. This reaction, can start up to 12 wk after initiation of drug
treatment and can occur after a dose increase.
Symptoms may persist or recur for several weeks after stopping
drug treatment.
Patients have prominent eosinophilia and often develop
hepatitis, exanthema, facial swelling, generalized edema, and
lymphadenopathy.
Carbamazepine, phenytoin, allopurinol and lamotrigine are
frequently implicated
DRESS
74. Hydralazine, propylthiouracil and procainamide
can cause an SLE-like syndrome.
It may be mild with arthralgias, fever, and rash or fairly
dramatic with serositis, high fevers, and malaise
The antinuclear antibody test is positive.
Penicillamine can cause SLE and other autoimmune
disorders like myasthenia gravis.
Some drugs can cause perinuclear antineutrophil
cytoplasmic autoantibodies (p-ANCA)–associated vasculitis. .
Other Autoimmune Diseases
75. Here a patient without previous pulmonary disease develops
respiratory symptoms, chest x-ray changes, deterioration of
pulmonary function, histologic changes, or several of these
findings in association with drug therapy.
Depending on the drug, it can cause interstitial fibrosis,
organizing pneumonia, asthma, noncardiogenic pulmonary
edema, pleural effusions, pulmonary eosinophilia,
pulmonary hemorrhage, or veno-occlusive disease
Pumonary Effects
78. Tubulointerstitial nephritis is the most common allergic
renal reaction
It is primary injury to renal tubules and interstitium
resulting in decreased renal function.
The acute form is most often due to allergic drug reactions
or to infections
The symptoms include fever, rash and enlarged kidneys
About 23% of patients have eosinophilia. There may be
hematuria, sterile pyuria or proteinuria
79. The drugs commonly implicated are antibiotics like
methicillin, anticonvulsants, diuretics and NSAIDS.
Corticosteroids are not useful in this setting.
Therapy consists of adequate fluid intake, which can require
several liters of extra fluid.
81. It is a form of a life-threatening skin condition, in which cell
death causes the epidermis to separate from the dermis.
The syndrome is thought to be a hypersensitivity complex that
affects the skin and the mucous membranes
This immune reaction can be triggered by drugs or infections.
Genetic factors are associated with a predisposition to SJS.
Slow acetylators, patients who are immunocompromised, and
patients with brain tumors undergoing radiotherapy with
concomitant antiepileptics are among those at most risk.
84. A life-threatening skin condition that is usually caused by a
reaction to drugs.
The disease causes the epidermis to detach the dermis, all
over the body.
Microscopically, TEN causes cell death throughout the
epidermis.
Often, the diagnosis is made clinically.
If the clinical history is consistent with Stevens–Johnson
syndrome, and the skin lesion covers greater than 30% of the
body surface area, the diagnosis of TEN is appropriate
86. To conclude..
Drug Hypersensitivity Syndrome is potentially life-
threatening with significant morbidity.
Prompt diagnosis is vital, along with identification and early
withdrawal of suspect medicines.
However many of these drug reactions are pharmacological
reactions rather than hypersensitivity reactions.
So in assessing drug reactions, a detailed clinical history and
careful documentation of reactions are most important.
