chemistry

Severe cutaneous adverse reactions

Severe cutaneous adverse reactions is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Severe cutaneous adverse reactions rather than just read about it. In short: Severe cutaneous adverse reactions (SCARs) are a group of potentially lethal adverse drug reactions that involve the skin and mucous membranes of various body openings such as the eyes, ears, and inside the nose, mouth, and lips. In more severe cases, SCARs also involves serious damage to internal organs.

Key takeaways

Severe cutaneous adverse reactions belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Severe cutaneous adverse reactions to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Severe cutaneous adverse reactions from memory before moving on to harder problems.

Reference excerpt

Severe cutaneous adverse reactions (SCARs) are a group of potentially lethal adverse drug reactions that involve the skin and mucous membranes of various body openings such as the eyes, ears, and inside the nose, mouth, and lips. In more severe cases, SCARs also involves serious damage to internal organs. SCARs includes five syndromes:

Drug reaction with eosinophilia and systemic symptoms (i.e. DRESS syndrome), also termed drug-induced hypersensitivity syndrome (DIHS); Stevens–Johnson syndrome (SJS); Toxic epidermal necrolysis (TEN); Stevens-Johnson/toxic epidermal necrolysis overlap syndrome (SJS/TEN); and Acute generalized exanthematous pustulosis (AGEP). The five disorders have similar pathophysiologies, i.e. disease-causing mechanisms, for which new strategies are in use or development to identify individuals predisposed to develop the SCARs-inducing effects of specific drugs and thereby avoid treatment with them. Maculopapular rash (MPR) is a less-well defined and benign form of drug-induced adverse skin reactions; while not classified in the SCARs group, it shares a similar pathophysiology with SCARs and is caused by some of the same drugs which cause SCARs. Adverse drug reactions are major therapeutic problems estimated to afflict up to 20% of inpatients and 25% of outpatients. About 90% of these adverse reactions take the form of benign morbilliform rash hypersensitivity drug reactions such as MPR. However, they also include more serious reactions:

Pseudo-allergic reactions in which a drug directly stimulates mast cells, basophils, and/or eosinophils to release pro-allergic mediators (e.g. histamine); Type I, Type II, and Type III hypersensitivity reactions of the adaptive immune system mediated by IgE, IgG, and/or IgM antibodies; and SCARs and MPR which are Type IV hypersensitivity reactions of the innate immune system initiated by lymphocytes of the T cell type and mediated by various types of leukocytes and cytokines. Type IV hypersensitivity reactions are off-target drug reactions, i.e. reactions in which a drug causes toxicity by impacting a biological target other than the one(s) for which it is intended. They are T cell-initiated delayed hypersensitivity reactions occurring selectively in individuals who may be predisposed to do so because of the genetically-based types of human leukocyte antigens (i.e. HLA) or T-cell receptors they express; the efficiency with which they absorb, distribute to tissues, metabolize, and eliminate a drug or drug metabolite; or less well-defined idiosyncrasies. Categorizing SCARs as a group focuses on the similarities and differences in their pathophysiologies, clinical presentations, instigating drugs, and recommendations for drug avoidance.

Types

SJS, TEN, and SJS/TEN

Stevens–Johnson syndrome, toxic epidermal necrolysis, and Stevens–Johnson syndrome/Toxic epidermal necrolysis overlap syndrome are a spectrum of Type IV, Subtype IVc, delayed hypersensitivity reactions, i.e. reactions initiated by CD8+ T cells and natural killer T cells. They are characterized initially by fever and flu-like symptoms followed within days by skin as well as mucous membrane blisters and denudation. Differentiation of the three disorders is based on the extent of disease with SJS involving <10%, SGS/TEN involving 10% to 30%, and TEN involving >30% of the total bodily skin area. This spectrum of disorders is complicated by inflammation in and damage to internal organs such as the liver and, less commonly, kidney and heart. More importantly, they are also complicated by sepsis due to the loss of skin and mucous membrane epithelial barriers. In one study, SJS, TEN, and SJS/TEN mortality rates were 4.8%, 19.4%, and 14.8%, respectively, with an important portion of the deaths due to bacterial sepsis, particularly in the acute, early stage of these disorders. The drugs most commonly triggering the SJS, TEN, and SJS/TEN spectrum of disorders are anti-infective sulfonamides, anticonvulsants (e.g. carbamazepine and lamotrigine), non-steroidal anti-inflammatory drugs, allopurinol, nevirapine, and chlormezanone. Allopurinol appears in some studies to be the most common instigator of these disorders. Any new biological or herbal remedy, it is suggested, should be considered a possible cause of these disorders under the proper clinical circumstances.

DRESS syndrome

The DRESS syndrome is a Type IV, Subtype IVb, hypersensitivity drug reaction, i.e. a reaction dependent on CD4(+) cells and the cell- and tissue-injuring action of eosinophils. Skin lesions inflict 73% to 100% of afflicted individuals; they are generally infiltrative macules and plaques. About 75% of cases exhibit facial edema. The syndrome is also associated with other maladies caused by high levels of blood eosinophils such as the various hypereosinophilia-related disorders: persistent asthma and allergic rhinitis and, more significantly, eosinophil-based and lymphocyte-based inflammation of the liver (>70% of cases), kidney (20% to 40% of cases), lung (~33% of cases), heart (4% to 27% of cases), and, uncommonly, the meninges, brain, gastrointestinal tract, and spleen. The disorder is lengthened and worsened in individuals that develop reactivation of latent viruses of the herpes viruses. The estimated mortality rate for the DRESS syndrome is about 10%. Allopurinol and sulfasalazine account for almost 66% of DRESS syndrome cases with minocycline being the third most common cause of the disorder; Strontium ranelate, leflunomide, dapsone, and nonsteroidal anti-inflammatory drugs (diclofenac, celecoxib, ibuprofen, and phenylbutazone) are less common causes of the disorder.

AGEP

AGEP is a rare Type IV, subtype IVd, hypersensitivity reaction dependent on neutrophils and characterized by the rapid formation of skin pustules on an erythematous background. In one study of 28 patients, the disorder was complicated by involvement of the kidney (36% of cases), lung (27%), and liver (11%). It is the least severe of the SCARs disorders, typically shows a mild course, and is rarely associated with severe complications although superinfection of skin lesions may be life-threatening.

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Worked examples

Example 1 — a first encounter with Severe cutaneous adverse reactions

Start with the simplest possible case. Write down what Severe cutaneous adverse reactions claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Severe cutaneous adverse reactions before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Severe cutaneous adverse reactions ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Severe cutaneous adverse reactions

In research: Severe cutaneous adverse reactions appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Severe cutaneous adverse reactions in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Severe cutaneous adverse reactions is common in secondary-school and first-year university syllabi. It links to neighbouring topics Drug eruptions, Medication side effects, Syndromes, so understanding it makes those chapters shorter.
In everyday life: Look for Severe cutaneous adverse reactions outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Severe cutaneous adverse reactions in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Severe cutaneous adverse reactions means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Severe cutaneous adverse reactions out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Severe cutaneous adverse reactions in simple terms?

Why does Severe cutaneous adverse reactions matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Severe cutaneous adverse reactions?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Severe cutaneous adverse reactions.