A patient with penicillin-induced

10.3 A patient with penicillin-induced

urticaria.

Diagnosis

The most important aspect in the diagnosis of a drug reaction is the medical history. Although diagnostic tests exist, they are still of limited practical value for the clinician in evaluating a patient with suspected drug eruptions. SPTs are useful in IgE-mediated reactions. A positive SPT indicates that IgE antibodies to the drug are present, but a

Drug allergy 157

such as RAST and ELISA can be used to detect IgE antibodies to aminoglycosides, sulphonamides, trimethoprim, insulin, and many β-lactam antibiotics. Serum tryptase estimation is employed to evaluate patients with suspected drug reaction. Tryptase is a protease found in mast cells and is released on mast cell degranulation. A raised tryptase does not establish the presence of drug-specific IgE antibodies, but is an indicator of mast cell mediator release. Skin biopsies are occasionally used to define specific histopathological lesions. It is useful in differentiating vasculitis and excluding bullous disease, not related to drug therapy, from SJS/TEN.

10.4 Diagnostic extracts (major and minor determinants) are commercially available for testing allergy to penicillin.

Management

The management of cutaneous drug eruptions involves identification and withdrawal of the drug, introduction of necessary supportive and suppressive treatment if the condition is severe, and considering alternative substitutes for the offending agent (10.5). Withdrawal of the drug is almost always prudent, and may immediately attenuate the reaction. In the case of mild type I reactions, such as urticaria and pruritus, antihistamines can be beneficial to suppress the symptoms with continuation of the treatment.

Certain cutaneous drug reactions, such as SJS, TEN, and some hypersensitivity reactions, need to be treated without delay because these medical emergencies are associated with considerable morbidity and mortality. The management and treatment of SJS and TEN are similar to treatment of burns with aggressive fluid management, nutritional support, and antibiotics. The role of corticosteroids is controversial in the

Allergy 158

efficient method wherein an unrelated alternative drug is chosen. This situation works well with antibiotics. The second option is to choose a medication not identical but potentially cross-reacting with the offending drug, for example cephalosporins for penicillin-sensitive patients. However, this should be done with caution, as immunological cross-reactivity between penicillins and cephalosporin may be as high as 15–25% for first generation cephalosporins, but appears to be lower for third generation cephalosporins. Potentially cross-reacting drugs should not be reintroduced, even in graded doses, for patients who have experienced SJS/TEN. The third choice is drug desensitization. It is possible sometimes to readminister the offending drug in a patient who has had a drug eruption. Re-administration is usually done with gradually escalating doses of the offending agent. Certain factors need to be taken into account when re- administering the medication. For IgE-mediated reactions, re-administration can precipitate anaphylaxis, while in exfoliative conditions, SJS and TEN, this is contraindicated.

10.5 Diagnostic approach to suspected drug allergy. (ID, intra-dermal test; RAST; radio allergen sorbent test; SPT, skin prick test.)

Drug allergy 159

Latex allergy

Latex is a natural product which comes from the light milky fluid that is extracted from the rubber tree. This milky fluid is often modified during the manufacturing process to form a latex mixture. A person can be allergic to the latex, or the mixture, or both. Incidence of latex allergy is now about 25% in health care workers, and 2–6% in the general population, due to the increased use of latex to protect ourselves from infections and other diseases (Table 10.4). The highest prevalence of latex allergy (20–68%) is found in patients with spina bifida or congenital urogenital abnormalities. Sensitization in these patients apparently follows multiple urinary tract, rectal, and thecal procedures, as well as multiple surgeries during early childhood. Patients with spina bifida also may have a genetic predisposition for latex sensitization.

There are three different types of reactions to natural rubber latex (10.6). They are irritation, delayed hyper-sensitivity (allergic CD) and immediate hypersensitivity (anaphylactic symptoms). The diagnosis of latex allergy includes serum IgE levels, specific IgE, SPT, and patch testing for CD. Treatment in an acute scenario is similar to the management of acute anaphylactic reactions. Latex-free

Table 10.4 Risk factors for latex sensitivity

• Patients with spina bifida • Patients with congenital genitourinary abnormalities • Health care workers • Rubber industry workers • Atopic individuals • Patients who have had multiple surgucal procedures • Patients with certain food allergies

resuscitation equipment must be available and routine care should employ non-latex supplies. Prevention and taking adequate precautions are important in avoiding further reactions (10.7). Patients allergic to latex are at times sensitive to certain foods, including bananas, avocados, chestnuts, apples, carrots, celery, papaya, kiwi, potatoes, tomatoes, and melons. Food sensitivity of those allergic to latex may possibly also include pears, peaches, cherries, pineapple, strawberries, figs, grapes, apricots, passion fruit, rye, hazel nuts, walnuts, soy beans, and peanuts. Type IV hyper-sensitivity is best treated with patient education to avoid further exposure.

Allergy 160

10.6 Irritant dermatitis is due to mechanical disruption of the skin due to rubbing of the gloves and accounts for the majority of latex-induced reactions. This is not immune mediated. The second most common is contact dermatitis. The least common, but potentially serious reactions, are the IgE-mediated type I reactions.