Cross-reactivity between penicillins and cephalosporins: clinical and immunologic studies

A survey of antibiotic prescribing and knowledge of penicillin allergy

BACKGROUND

Cephalosporins can cause allergic reactions in patients with penicillin (PCN) allergy. Physicians' prescribing habits for patients with PCN allergy can vary.

OBJECTIVES

1) Survey community and academic physicians, students, residents, and allergists on their tendencies to prescribe cephalosporins and/or perform PCN skin testing in patients with different histories of PCN allergy. 2) Evaluate PCN allergy knowledge in these groups.

METHODS

A questionnaire consisting of four case scenarios and five true/false questions on PCN allergy was distributed at various conferences and by mailings.

RESULTS

Three hundred seventy-eight completed surveys were analyzed. Given a patient with a history of rash with PCN, an equal number of allergists and nonallergists (36%) prescribed cephalosporins, although there was a difference between pediatricians (56%) and internists (22%). Given a history of PCN anaphylaxis, no allergists but 11% of nonallergists prescribed a cephalosporin. Skin testing was infrequently requested by nonallergists. The correct response rate for the true/false questions was 89% for allergists, community (63%) and academic (67%) physicians, pediatricians (61%), internists (67%), residents (68%), and students (68%). Pediatric residents had the highest (74%) and community pediatricians the lowest (59%) correct response rate.

CONCLUSIONS

There is marked variation in prescribing cephalosporins and in requesting PCN skin testing in patients with varied histories of PCN allergy. The survey results indicate a need for increased PCN allergy education.

In vitro T-cell responses to beta-lactam drugs in immediate and nonimmediate allergic reactions

BACKGROUND

beta-Lactam drugs may induce both cellular and humoral allergic reactions, and there is evidence that T cells play an important role in the pathogenesis of these reactions. The aim of this work was to assess the sensitivity and specificity of the lymphocyte transformation test (LTT) as an in vitro diagnostic tool, in patients with either an immediate or a nonimmediate reaction to penicillin G and/or amoxicillin.

METHODS

Fifty patients with a well-documented history of allergic reactions to beta-lactams (31 immediate and 19 nonimmediate) were studied by means of skin tests (prick and intradermal), radioallergosorbent test (RAST), and, when necessary, controlled administration of the drug. Twenty-eight healthy subjects with good tolerance to penicillins served as controls. LTT was performed in all subjects.

RESULTS

Skin tests were positive in 77.4% of the patients with immediate reactions and in 36.8% of those with nonimmediate reactions. The overall sensitivity of LTT in the allergic patients was 62%, but, when analyzed separately, sensitivity was 64.5% for the immediate group and 57.9% for the nonimmediate group. The LTT specificity was 92.8%.

CONCLUSION

The LTT should be considered a useful in vitro diagnostic tool to identify subjects allergic to penicillins, especially patients with nonimmediate reactions where the LTT has a better diagnostic value than skin tests. Interestingly, positive T-cell proliferative responses can be observed 10 or more years after the occurrence of the reaction without further exposure to the drug.

Lack of allergic cross-reactivity to cephalosporins among patients allergic to penicillins

There are some contradicting data about clinical allergic cross-reactivity to cephalosporins among patients who have had a previous allergic reaction to penicillins. The purpose of this study was to assess the safety of administering cephalosporins to penicillin-allergic patients. The diagnosis of penicillin allergy was made by positive skin tests to penicillin reagents and/or provocation tests with the penicillin suspected of causing the allergic reaction. To assess the clinical tolerance to cephalosporins, 41 well-characterized penicillin allergic patients diagnosed by positive skin tests and/or provocation tests were challenged with three cephalosporins that do not share the same side chain to the penicillin that induced the reactions: cephazoline, cefuroxime and ceftriaxone. Skin prick and intradermal tests with all cephalosporins tested were negative. All penicillin-allergic patients tolerated therapeutic doses of the three cephalosporins tested (cephazoline, cefuroxime and ceftriaxone) without any ill effect. These results indicate that the risk of suffering from an allergic reaction on administering cephalosporins to penicillin-allergic patients seems to be very low, provided that cephalosporins with a different side chain to the penicillin responsible for the allergic reaction are used.

Immediate allergic reactions to cephalosporins: cross-reactivity and selective responses

BACKGROUND

After penicillins, cephalosporins are the most important beta-lactams inducing IgE-mediated reactions. Responses may be selective or cross-reactive with common beta-lactam determinants. Unlike determinants derived from benzylpenicillin, cephalosporin allergenic determinants have not been properly identified, even though a wide variety of these beta-lactams is currently used.

OBJECTIVE

We sought to evaluate the IgE response in subjects with immediate allergic reactions to injectable cephalosporins and to assess their reactivity to different penicillins and cephalosporins.

METHODS

We studied 30 subjects with immediate reactions to one or more of the following cephalosporins: ceftriaxone, cefotaxime, ceftazidime, and cefuroxime. Skin tests and in vitro-specific IgE antibody assays were performed for major and minor determinants of penicillin G, amoxicillin, and ampicillin, as well as for the culprit cephalosporins. Responses to cephalosporins other than the culprit ones were also studied by using skin testing.

RESULTS

Twenty-six patients (group A, 86.7%) displayed skin test and RAST negativity to penicillin determinants and skin test positivity to cephalosporins, with RAST confirmation in 9 patients. Four subjects (group B, 13.3%) had a positive response to penicillin determinants. In group A two patterns of reactivity were observed: one characterized by a response only to the culprit cephalosporin (n = 15, 57.7%) and the other by positive responses to different cephalosporins, including the responsible cephalosporins (n = 11, 42. 3%).

CONCLUSION

Most patients with a history of immediate reactions to cephalosporins are sensitized to determinants generated only by cephalosporins (group A), although a small percentage react to penicillin determinants (group B). Some patients from group A responded only to the culprit cephalosporin, but others reacted to different cephalosporins. These findings can be explained in terms of either selective response to unique determinants or cross-reactivity.

Penicillin allergy: prevalence of vague history in skin test-positive patients

OBJECTIVE

Penicillin (PCN) skin testing is a reliable tool for predicting which patients can safely receive the antibiotic. Depending on the study, 7% to 76% of patients who have a history of PCN allergy have positive PCN skin tests. Many physicians approach patients who have a vague history of PCN allergy less cautiously than they approach those who have a convincing history suggestive of an IgE-mediated reaction. We reviewed the published literature to determine how many patients who had a history of PCN allergy and who were skin test-positive had a vague history of allergy.

DATA SOURCES

By cross-referencing the keywords "penicillin" and "skin test," an Ovid MEDLINE search for English language studies published from 1966 to 1998 was performed.

STUDY SELECTION

Studies in which history positive/skin test-positive patients were identified, and which contained documentation of the type of previous reaction in these patients, were included in the analysis. The MEDLINE search revealed 295 English language articles, of which 27 fulfilled the inclusion criteria. Three additional studies published prior to 1966 (and therefore not available through MEDLINE) also were found, bringing the total to 30. A "convincing" history was defined to be one likely to be IgE-mediated (such as anaphylaxis, urticaria, angioedema or pruritic rash). A "vague" history was one unlikely to be IgE-mediated (such as maculopapular rash, GI symptoms, or an unknown reaction).

RESULTS

Overall, 347/1063, or 33%, of history positive/skin test-positive patients had a vague PCN allergy history, with a range of 0% to 70% among the 30 studies.

CONCLUSION

A large proportion of patients who have PCN-specific IgE antibodies, as determined by skin testing, have vague PCN allergy histories. These results therefore, indicate that, like patients with convincing histories, patients with vague allergic histories should undergo PCN skin testing prior to PCN administration.

Recognising antibacterial hypersensitivity in children

Adverse reactions to antibacterial agents are not uncommon in children. They are classified as 'immediate' or 'nonimmediate' according to the time interval between drug administration and onset. Immediate reactions occur within 1 hour and are manifested by urticaria and/or angioedema, bronchospasm and anaphylactic shock; immunological reactions are mediated by IgE antibodies. The main nonimmediate reactions (occuring after more than 1 hour) are maculopapular rash, urticaria and serum sickness; T lymphocytes may participate in maculopapular rash. Clinical assessment of such reactions is complex. The patient's history is fundamental; the allergological examination includes in vivo and in vitro tests selected on the basis of the clinical features and the phase of reaction. In the late phase, prick and intradermal tests are sensitive in evaluating beta-lactam allergy. Together with delayed-reading intradermal testing, patch testing seems to be useful in diagnosing maculopapular reactions to systemically administered aminopenicillins. Determination of specific IgE levels is the most common in vitro method for diagnosing immediate reactions. In the acute phase, serum tryptase and urinary N-methylhistamine assays are reliable in diagnosing type I pathogenic mechanisms in immediate reactions. Unfortunately, there are few in vitro tests for evaluating other reactions, and most are not fully validated. In selected cases, provocation tests should be performed.

Clinical approach to penicillin-allergic patients: a survey

BACKGROUND

Approximately 10% of individuals report a history of penicillin allergy.

OBJECTIVE

We chose to survey various physician groups to determine how they would manage penicillin-allergic patients who present with an infectious process for which penicillin is the drug of choice.

METHODS

In situations where penicillin was the drug of choice, physicians were asked to choose the type of antibiotic treatment for patients who presented with diseases of varying severity and who had either vague or convincing penicillin-allergic histories.

RESULTS

A total of 601 surveys were mailed and 93 (16%) were returned. For those patients who present with a vague history of penicillin allergy, 58% and 59% of the physicians surveyed stated that they would choose cephalosporins for individuals with mild and moderate diseases, respectively. In contrast, in the vague penicillin history/severe disease scenario, physicians were split between choosing cephalosporins (42% of responders) and vancomycin (40% of responders). For those patients who present with a convincing history of penicillin allergy, 55% of the physicians chose erythromycin for individuals with mild disease; 44% chose quinolones for individuals with moderate disease, and 63% chose vancomycin for individuals with severe disease. In each of the three disease severities, physicians were significantly more likely to choose cephalosporins for patients with a vague history of penicillin allergy than for patients with a convincing history (each P<10-5).

CONCLUSION

The choice of antibiotics is influenced both by the type of penicillin allergic history and by the severity of the disease process to be treated. To decrease the use of broad-spectrum antibiotics in patients labeled "penicillin-allergic", an effort should be made to identify, by skin testing, those patients who lack penicillin-specific IgE antibodies.

Allergy to beta-lactam antibiotics in children

BACKGROUND

Skin tests with soluble beta-lactams can be used to diagnose immediate and delayed hypersensitivity (HS) reactions to beta-lactam antibiotics. Very few studies have been performed with children with suspected beta-lactam allergy. In these studies, immediate HS to beta-lactams was diagnosed by skin tests in 4.9% to 40% of children. The diagnostic and predictive values of immediate responses in skin tests are good, because very few children with negative skin test results have positive oral challenge (OC) test results. Delayed responses in skin tests (intradermal and patch tests) have been reported in adult patients and children suffering with urticaria, angioedema, and maculopapular rashes during treatments with beta-lactam antibiotics. However, the diagnostic and predictive values of late responses are unknown. Semi-late responses in skin tests with beta-lactams have never been studied in adults or children.

OBJECTIVES

The aims of this study were to confirm or rule out the diagnosis of allergy to beta-lactams in children with histories of adverse reactions to these antibiotics, to determine whether allergic children were sensitized to one or several classes of beta-lactams, and to evaluate the frequency and diagnostic value of immediate, accelerated, and delayed responses in skin tests with beta-lactam antibiotics in children.

METHODS

We studied 325 children with suspected beta-lactam allergy. Skin tests (prick and intradermal) were performed with soluble forms of the suspected (or very similar) beta-lactams and with one or several beta-lactams from other classes. The reaction was assessed after 20 minutes (immediate), 8 hours (accelerated), and 48 to 72 hours (delayed). OCs with the suspected beta-lactams were performed in patients with negative skin test results, except those with severe serum sickness-like reactions and potentially harmful toxidermias.

RESULTS

Skin tests and OCs led to the diagnosis of beta-lactam allergy in 24 (7.4%) and 15 (4.6%) of the children, respectively. Thus, only 12% of the children were diagnosed as allergic to beta-lactams by means of skin tests and OC. HS to beta-lactams was suspected from clinical history in 30 (9.2%) children reporting serum sickness-like reactions and potentially harmful toxidermias. In a few children, we diagnosed food allergy and intolerance to excipients or nonsteroidal antiinflammatory drugs. No cause was found in the other children. Based on skin tests and OC, the prevalences of immunoglobulin E-dependent and of semi-late or delayed sensitizations to beta-lactam assessed were similar (6.8% vs 5.2%, respectively). Most immunoglobulin E-dependent sensitizations were diagnosed by means of skin tests (86.4%). In contrast, most semi-late and delayed sensitizations were diagnosed by OC (70.6%). The likelihood of beta-lactam allergy was significantly higher for anaphylaxis (42.9% vs 8.3% in other reactions) and immediate reactions (25% vs 10% in accelerated and delayed reactions). Of the children diagnosed as allergic to beta-lactam by means of skin tests, OC, and clinical history, 11.7% were sensitized to several classes of beta-lactams. The risk was significantly higher in children with anaphylaxis (26. 7% vs 7.5% of the children with other reactions) and in children reporting immediate reactions (33.3% vs 8.5% of the children with accelerated and delayed reactions). Finally, age, sex, personal history of atopy, number of reactions to beta-lactams, and number of reactions to other drugs were not significant risk factors for beta-lactam allergy.

CONCLUSION

The skin tests were safe, and the immediate reaction to skin tests successfully diagnosed allergy to beta-lactam antibiotics in children reporting reactions suggestive of immediate HS. In contrast, most accelerated and delayed reactions were diagnosed by OC. Thus, our results suggest that the diagnostic and predictive values of skin tests for nonimmediate HS to beta-lactams in children are low. (ABSTRACT TRU

Recognition of local anesthetics by alphabeta+ T cells

Patients with drug allergy show a specific immune response to drugs. Chemically nonreactive drugs like, for example, local anesthetics are directly recognized by alphabeta+ T cells in an HLA-DR restricted way, as neither drug metabolism nor protein processing is required for T cell stimulation. In this study we identified some of the structural requirements that determine cross-reactivity of T cells to local anesthetics, with the aim to improve the molecular basis for the selection of alternatives in individuals sensitized to a certain local anesthetic and to better understand presentation and T cell recognition of these drugs. Fifty-five clones (52 lidocaine specific, three mepivacaine specific from two allergic donors) were analyzed. Stimulatory compounds induced a down-regulation of the T cell receptor, demonstrating that these non-peptide antigens are recognized by the T cell receptor itself. A consistent cross-reactivity between lidocaine and mepivacaine was found, as all except one lidocaine specific clone proliferated to both drugs tested. Sixteen chemically related local anesthetics (including ester local anesthetics, OH- and desalkylated metabolites) were used to identify structural requirements for T cell recognition. Each of the four clones examined in detail was uniquely sensitive to changes in the structures of the local anesthetic: clone SFT24, i.e., did not recognize any of the tested OH- or desalkylated metabolites, while the clone OFB2 proliferated to all OH-metabolites and other differently modified molecules. The broadly reactive clone OFB2 allowed us to propose a model, suggesting that the structure of the amine side chain of local anesthetics is essential for recognition by the T cell receptor.

Determination of IgE antibodies to the benzylpenicilloyl determinant: a comparison of the sensitivity and specificity of three radio allergo sorbent test methods

The quantitation of in vitro IgE antibodies to the benzylpenicilloyl determinant (BPO) is a useful tool for evaluating suspected penicillin allergic subjects. Although many different methods have been employed, few studies have compared their diagnostic specificity and sensitivity. In this study, the sensitivity and specificity of three different radio allergo sorbent test (RAST) methods for quantitating specific IgE antibodies to the BPO determinant were compared. Thirty positive control sera (serum samples from penicillin allergic subjects with a positive clinical history and a positive penicillin skin test) and 30 negative control sera (sera from subjects with no history of penicillin allergy and negative skin tests) were tested for BPO-specific IgE antibodies by RAST using three different conjugates coupled to the solid phase: benzylpenicillin conjugated to polylysine (BPO-PLL), benzylpenicillin conjugated to human serum albumin (BPO-HSA), and benzylpenicillin conjugated to an aminospacer (BPO-SP). Receiver operator control curves (ROC analysis) were carried out by determining different cut-off points between positive and negative values. Contingence tables were constructed and sensitivity, specificity, negative predictive values (PV-), and positive predictive values (PV+) were calculated. Pearson correlation coefficients (r) and intraclass correlation coefficients (ICC) were determined and the differences between methods were compared by chi 2 analysis. Analysis of the areas defined by the ROC curves showed statistical differences among the three methods. When cut-off points for optimal sensitivity and specificity were chosen, the BPO-HSA assay was less sensitive and less specific and had a lower PV- and PV+ than the BPO-PLL and BPO-SP assays. Assessment of r and ICC indicated that the correlation was very high, but the concordance between the PLL and SP methods was higher than between the PLL and HSA or SP and HSA methods. We conclude that for quantitating IgE antibodies by RAST to the BPO determinant, BPO-SP or BPO-PLL conjugates offer advantages in sensitivity and specificity compared with BPO-HSA. These results support and extend previous in vitro studies by our group and highlight the importance of the carrier for RAST assays.

Quantification of penicillin-G and procaine in equine urine and plasma using high-performance liquid chromatography

A rapid and sensitive method for the extraction and quantification of penicillin-G and procaine in horse urine and plasma samples has been successfully developed. The method involves the use of solid-phase extraction (SPE) for penicillin-G, liquid-liquid extraction (LLE) for procaine, and high-performance liquid chromatography (HPLC) for the quantification of penicillin-G and procaine. The new method described here has been successfully applied in the pharmacokinetic studies of procaine, penicillin-G and procaine-penicillin-G administrations in the horse.

The presence of latex can induce false-positive skin tests in subjects tested with penicillin determinants

Latex allergens are ubiquitous, and exposure may occur from different sources in the medical environment and in daily life. The observation that subjects with latex allergy were skin test positive to major and minor determinants of penicillins led our group to carry out an investigation to try to explain these findings. A group of 20 subjects with a history of allergy to latex and with positive skin tests for, but good tolerance of, penicillins was studied. The presence of latex contaminants was studied by RAST and RAST inhibition. Sixteen of the subjects were positive to at least one of the penicillin determinants used, and 14 (87%) of these were positive to at least two determinants. Repetition of skin tests using the container without a stopper changed the skin test results to negative in almost all cases, indicating that some trace contaminants had still been present. RAST-inhibition studies showed that in all penicillin determinants there were trace amounts of latex allergens varying between 3 and 0.03 micrograms/ml. These results indicate that skin tests with penicillin in subjects allergic to latex may give false-positive results and lead to such patients being falsely diagnosed as allergic to betalactams when penicillins are stored in containers with rubber stoppers.

Hypersensitivity to cefuroxime with good tolerance to other betalactams

A 60-year-old man developed an anaphylactic reaction immediately after administration of intramuscular sodium cefuroxime. By means of oral controlled challenge, the reaction was reproduced with a smaller dose of cefuroxime axetil. Cross-reactivity with other betalactam antibiotics was ruled out by in vivo tests. This case supports once again the relevance of the side-chain in betalactam allergy.

Immediate allergic reactions to amoxicillin

A large group of patients with suspected allergic reactions to beta-lactam antibiotics was evaluated. A detailed clinical history, together with skin tests, RAST (radioallergosorbent test), and controlled challenge tests, was used to establish whether patients allergic to beta-lactam antibiotics had selective immediate allergic responses to amoxicillin (AX) or were cross-reacting with other penicillin derivatives. Skin tests were performed with benzylpenicilloyl-poly-L-lysine (BPO-PLL), benzylpenicilloate, benzylpenicillin (PG), ampicillin (AMP), and AX. RAST for BPO-PLL and AX-PLL was done. When both skin test and RAST for BPO were negative, single-blind, placebo-controlled challenge tests were done to ensure tolerance of PG or sensitivity to AX. A total of 177 patients were diagnosed as allergic to beta-lactam antibiotics. We selected the 54 (30.5%) cases of immediate AX allergy with good tolerance of PG. Anaphylaxis was seen in 37 patients (69%), the other 17 (31%) having urticaria and/or angioedema. All the patients were skin test negative to BPO; 49 of 51 (96%) were also negative to MDM, and 44 of 46 (96%) to PG. Skin tests with AX were positive in 34 (63%) patients. RAST was positive for AX in 22 patients (41%) and to BPO in just 5 (9%). None of the sera with negative RAST for AX were positive to BPO. Challenge tests with AX were performed in 23 subjects (43%) to establish the diagnosis of immediate allergic reaction to AX, and in 15 cases (28%) both skin test and RAST for AX were negative. PG was well tolerated by all 54 patients. We describe the largest group of AX-allergic patients who have tolerated PG reported so far. Diagnosis of these patients can be achieved only if specific AX-related reagents are employed. Further studies are necessary to determine the exact extent of this problem and to improve the efficacy of diagnostic methods.

Differences in serum IgE antibody activity to benzylpenicillin and amoxicillin measured by RAST in a group of penicillin allergic patients

To determine the influence of the acyl side chain on the IgE antibody specificity of the two most common penicillins inducing allergic reactions in our community, benzylpenicillin (BP) and amoxicillin (AX), IgE positive sera from a group of 24 patients allergic to penicillin were studied. RAST was determined in parallel to benzyl penicilloyl-polylysine (BPO-PLL) and amoxicilloyl-polylysine (AX-PLL) in each serum, and values greater than an established coefficient of variation of 15% were considered as different for either of the haptens used (BP and AX). 16 sera proved to be more positive to BP (Group A), six to AX (Group B) and in two IgE was positive to both haptens with a similar value (Group C). RAST titration concentration effect curves and RAST inhibition studies with a pool of sera from each group (A, B, C) and individual sera showed that most of them were more specific for either BPO or AX, a minority being of similar value to both. These findings indicate that the side chain structure of penicillins is relevant in the constitution of the antigenic determinant, although in some instances the common chemical structure of betalactam is recognised mainly by the IgE antibodies. The clinical relevance of these data needs to be established.

Tolerance to aztreonam in patients allergic to beta-lactam antibiotics

To evaluate the safe use of aztreonam (AZT) in patients allergic to penicillins and other beta-lactam antibiotics we studied 29 patients from a group of subjects allergic to beta-lactams, diagnosed by presenting systemic reactions after skin tests or challenge tests. Skin tests with benzylpenicilloyl (BPO), benzylpenicilloate, benzylpenicillin, ampicillin, amoxicillin, cephamandole and AZT, radioallergosorbent test (RAST) to BPO and AZT, RAST inhibition and challenge tests were performed. One patient was skin test-positive to AZT, another patient was RAST AZT-positive. IgE antibodies were specific to AZT as demonstrated by RAST inhibition studies with AZT coupled to epsilon-amino caproic acid. Nevertheless, AZT was unable to inhibit either a pool of sera or individual sera positive to BPO. Although all our 29 patients tolerated the administration of AZT (including those with skin test or RAST positive) and AZT appears to be safe in these subjects, this does not indicate that all beta-lactam-allergic patients tolerate AZT administration.

Delayed allergic reactions to beta-lactams. Four cases with intolerance to amoxicillin or ampicillin and good tolerance to penicillin G and V

We present four cases of delayed allergic skin reactions to amoxicillin or ampicillin with good tolerance to benzyl penicillin and phenoxymethyl penicillin. The clinical symptoms reported by the patients, the intradermal skin tests and the controlled challenge results suggested that the mechanism was cellular mediated. In two patients these findings were supported by histopathological studies. Although delayed-type hypersensitivity reactions to beta-lactams with positive skin test seem rare, they can occur to penicillins in allergic patients. The production of these reactions by amoxicillin or ampicillin with good tolerance to benzyl penicillin and phenoxymethyl penicillin emphasizes the role of the side chain in inducing allergic reactions to beta-lactams.

Allergy to penicillin with good tolerance to other penicillins; study of the incidence in subjects allergic to beta-lactams

Two hundred and eighty-eight subjects with a history of allergy to penicillin were studied for objective proof of their allergy. On the basis of skin tests, specific IgE antibody measurements and direct challenge tests. 64 patients (22%) were shown objectively to be allergic to one or more penicillins. The following tests were carried out: skin tests to benzyl-penicilloyl poly-L-lysine (BPO-PLL), minor determinant mixture (MDM), amoxycillin (AX) and ampicillin (AMP), in-vitro IgE antibody measurement to benzyl-penicilloyl (BPO) and AX and challenge with benzylpenicillin (BP), phenoxy-methyl-penicillin (PV) and amoxycillin. Forty-four cases were found to respond to benzyl or phenoxymethyl-penicillin, however, 20 were shown to be sensitive to amoxycillin and unresponsive to tests with other penicillins. The contribution that any individual test gave for establishing the diagnosis was 21.8% for skin testing with BPO-PLL, 9.3% with MDM and 12.5% with AX. Nine point three per cent were RAST positive to BPO and 1.5% to AX; 7.8% developed a positive response after challenge to BP, 7.8% to PV and 14% to AX. In 16% of the 64 positive cases more than one test was found to be positive. The challenge tests suggested that not all the penicillin-sensitive subjects had IgE-mediated reactions implying other immunological mechanisms. These results clearly demonstrate the importance of side chain-specific diagnostic reagents and challenge tests. Thirty-one per cent of the positive group or 6.9% of the total group would have been missed in this study using benzyl or phenoxymethyl-penicillin diagnostic reagents alone.

Safety of parenteral third-generation cephalosporins

Knowledge of side effects associated with different cephalosporins may be of help to prescribers. There are several side effects that are common to all cephalosporins, but overall, cefotaxime and ceftizoxime cause the fewest adverse reactions. Bleeding is probably the most common serious side effect of cephalosporins. Moxalactam causes coagulopathy and bleeding more often than do other cephalosporins, probably because it is carboxylated and has a methylthiotetrazole side chain. Cefoperazone also has a methylthiotetrazole side chain and may cause bleeding, particularly when used in doses greater than 4 g per day. Ceftriaxone has a similar side chain and there is some evidence that it can induce a coagulopathy. Coagulation tests should be monitored when any of the third-generation cephalosporins are given to patients with a high risk of bleeding. Disulfiram-like reactions are also related to the side chains associated with coagulation defects and have been reported when patients receiving cefoperazone, moxalactam, or ceftriaxone have ingested alcohol. Seizures have been reported with ceftazidime, but are uncommon. Hematologic reactions are rare with all third-generation cephalosporins. Benign diarrhea and Clostridium difficile colitis probably occur most often with moxalactam, cefoperazone, ceftazidime, and ceftriaxone, but there are few good data on this issue. Ceftriaxone has the unique ability to cause sludge (also referred to as pseudolithiasis) to form in the gallbladder, particularly in children. This may be associated with nausea, anorexia, epigastric distress, and colic, and is usually detected using ultrasonography. The sludge dissolves and symptoms subside after therapy is discontinued. None of the third-generation cephalosporins is clearly significantly nephrotoxic, even when combined with aminoglycosides. Most of the third-generation cephalosporins have surprisingly few serious side effects, which make them attractive for use in the treatment of a wide variety of serious infections.

Drug allergy. Best diagnostic and treatment approaches

The problems in identifying and managing drug allergy are myriad, primarily because of the number of possible agents involved, the lack of objective diagnostic methods, and the varied signs and symptoms that may occur. Allergic reactions can be life-threatening and are avoidable in most cases. A careful and serious approach is important because the effect of medical decisions can be significant. Physicians should keep in mind that an allergic reaction to any drug can occur in any patient at any time.