Reduced toxicity with gradual initiation of trimethoprim-sulfamethoxazole as primary prophylaxis for Pneumocystis carinii pneumonia: AIDS Clinical Trials Group 268

Skin eruptions in children: Drug hypersensitivity vs viral exanthema

Childhood rashes or exanthemas are common and are usually relatively benign. There are many causes of rash in children, including mainly viruses, and less often bacterial toxins, drugs, allergens and other diseases. Viral exanthema often appears while children are taking a medication in the course of a viral infection; it can mimic drug exanthema and is perceived as a drug allergy in 10% of cases. In the vast majority of cases, the distinction between virus-induced and drug-induced skin eruption during the acute phase is not possible. The drugs most commonly implicated are beta-lactams (BL) and non-steroidal anti-inflammatory drugs (NSAIDs). Viruses, commonly Epstein-Barr virus (EBV), human herpesvirus 6 (HHV6) and cytomegalovirus (CMV), and the bacterium, Mycoplasma pneumoniae, may cause exanthema either from the infection itself (active or latent) or because of interaction with drugs that are taken simultaneously. Determination of the exact diagnosis requires a careful clinical history and thorough physical examination. Haematological and biochemical investigations and histology are not always helpful in differentiating between the two types of exanthema. Serological and polymerase chain reaction (PCR) assays can be helpful, although a concomitant acute infection does not exclude drug hypersensitivity. A drug provocation test (DPT) is although considered the gold standard for the diagnosis and is not preferred by the patients. Skin tests are not well tolerated, and in vitro tests, such as the basophil activation test and lymphocyte transformation, are of low sensitivity and specificity and their relevance is debatable. Based on current evidence, we propose a systematic clinical approach for timely differential diagnosis and management of rashes in children who present a cutaneous eruption while receiving a drug.

Pneumocystis pneumonia in HIV-1-infected patients

Pneumocystis pneumonia (PCP) is an opportunistic disease that mainly affects patients with a deficiency of cell-mediated immunity, especially acquired immunodeficiency syndrome (AIDS). The incidence of PCP in these patients has declined substantially owing to the widespread use of antiretroviral therapy and PCP prophylaxis. However, PCP is still a major AIDS-related opportunistic infection, particularly in patients with advanced immunosuppression in whom human immunodeficiency virus type 1 (HIV-1) infection remains undiagnosed or untreated. The clinical manifestations, diagnosis, treatment, and prevention of PCP in patients with HIV-1 infection are addressed in this review.

A Quantitative Model to Estimate Drug Resistance in Pathogens

Pneumocystis pneumonia (PCP) is an opportunistic infection that occurs in humans and other mammals with debilitated immune systems. These infections are caused by fungi in the genus Pneumocystis, which are not susceptible to standard antifungal agents. Despite decades of research and drug development, the primary treatment and prophylaxis for PCP remains a combination of trimethoprim (TMP) and sulfamethoxazole (SMX) that targets two enzymes in folic acid biosynthesis, dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS), respectively. There is growing evidence of emerging resistance by Pneumocystis jirovecii (the species that infects humans) to TMP-SMX associated with mutations in the targeted enzymes. In the present study, we report the development of an accurate quantitative model to predict changes in the binding affinity of inhibitors (K_i, IC₅₀) to the mutated proteins. The model is based on evolutionary information and amino acid covariance analysis. Predicted changes in binding affinity upon mutations highly correlate with the experimentally measured data. While trained on Pneumocystis jirovecii DHFR/TMP data, the model shows similar or better performance when evaluated on the resistance data for a different inhibitor of PjDFHR, another drug/target pair (PjDHPS/SMX) and another organism (Staphylococcus aureus DHFR/TMP). Therefore, we anticipate that the developed prediction model will be useful in the evaluation of possible resistance of the newly sequenced variants of the pathogen and can be extended to other drug targets and organisms.

Complications and outcomes of trimethoprim-sulphamethoxazole as chemoprophylaxis for pneumocystis pneumonia in renal transplant recipients

BACKGROUND

Following a pneumocystis pneumonia (PCP) outbreak in our nephrology unit, all transplant patients were offered chemoprophylaxis with trimethoprim-sulphamethoxazole (TMP-SMX) as the first line agent. A high rate of complications was noted. We aimed to quantify TMP-SMX associated adverse events and evaluate its prophylactic benefit in their light. Potential risk factors for complications' development were also investigated.

METHOD

This was an observational study of outcomes in transplant recipients commenced on TMP-SMX prophylaxis for 1year period. End-points were adverse events due to TMP-SMX, the additional medical burden resulting from these events, and PCP diagnosis.

RESULTS

290 patients commenced on TMP-SMX. 110 (38%) developed complications with most common being rise in serum creatinine (Cr) (n = 63, 22%) followed by gastrointestinal symptoms (n = 15, 5%), and leucopenia (n = 5, 2%). PCP incidence fell from 19 cases in 19 months to 2 cases in 12 months. Baseline renal function (P = 0.019) was an independent predictors for developing rise in Cr with TMP-SMX.

CONCLUSION

Use of chemoprophylaxis is an effective strategy in dealing with a PCP outbreak but can lead to a high number of complications. Rises in serum Cr can cause significant concern and increase in the number of investigations.

A dose-escalation regimen of trimethoprim-sulfamethoxazole is tolerable for prophylaxis against Pneumocystis jiroveci pneumonia in rheumatic diseases

OBJECTIVE

To investigate the safety and efficacy of a dose-escalation regimen of trimethoprim-sulfamethoxazole (TMP/SMX) for prophylaxis against Pneumocystis jiroveci pneumonia (PCP) in rheumatic diseases.

METHODS

Data from 41 patients, who received glucocorticoids with or without immunosuppressive agents and prophylactic use of TMP/SMX, were retrospectively analyzed. Thirteen patients were started on a daily dose of 10% of single-strength (SS) TMP/SMX, which was increased gradually (dose-escalation group), while 28 patients were started on 1 SS tablet daily (routine group).

RESULTS

In the dose-escalation group, the retention rate was 100% at 6 months. In the routine group, 5 patients discontinued TMP/SMX; the retention rate was 82.1%. Moreover, the retention rate when taking a daily dose of 50% or more of SS TMP/SMX, or 1 SS tablet thrice-weekly, was significantly higher in the dose-escalation group (100 versus 71.4%, P = 0.032). No PCP was observed in the dose-escalation group; however, 1 patient in the routine group, who had discontinued TMP/SMX, developed PCP. The rate of adverse effects was less, although nonsignificant, in the dose-escalation group (30.8 versus 46.4%, P = 0.344).

CONCLUSIONS

In rheumatic diseases, a dose-escalation regimen of TMP/SMX resulted in a higher retention rate and was safer than the routine regimen.

Human N-acetyltransferase 1 *10 and *11 alleles increase protein expression through distinct mechanisms and associate with sulfamethoxazole-induced hypersensitivity

OBJECTIVES

N-acetyltransferase 1 (NAT1) metabolizes drugs and environmental carcinogens. NAT1 alleles *10 and *11 have been proposed to alter protein level or enzyme activity compared with wild-type NAT1 *4 and to confer cancer risk, through uncertain pathways. This study characterizes regulatory polymorphisms and underlying mechanisms of NAT1 expression.

METHODS

We measured allelic NAT1 mRNA expression and translation, as a function of multiple transcription start sites, alternative splicing, and three 3'-polyadenylation sites in human livers (one of which was discovered in this study), B lymphocytes, and transfected cells. In a clinical study of 469 patients with HIV/AIDS treated with the NAT1/NAT2 substrate sulfamethoxazole (SMX), associations were tested between SMX-induced hypersensitivity and NAT1 *10 and *11 genotypes, together with known NAT2 polymorphisms.

RESULTS

NAT1 *10 and *11 were determined to act as common regulatory alleles accounting for most NAT1 expression variability, both leading to increased translation into active protein. NAT1 *11 (2.4% minor allele frequency) affected 3'-polyadenylation site usage, thereby increasing formation of NAT1 mRNA with intermediate length 3'-untranslated region (major isoform) at the expense of the short isoform, resulting in more efficient protein translation. NAT1 *10 (19% minor allele frequency) increased translation efficiency without affecting 3'-untranslated region polyadenylation site usage. Livers and B-lymphocytes with *11/*4 and *10/*10 genotypes displayed higher NAT1 immunoreactivity and NAT1 enzyme activity than the reference genotype *4/*4. Patients who carry *10/*10 and *11/*4 (fast NAT1 acetylators) were less likely to develop hypersensitivity to SMX, but this was observed only in individuals who are also carrying a slow NAT2 acetylator genotype.

CONCLUSION

NAT1 *10 and *11 significantly increase NAT1 protein level/enzyme activity, enabling the classification of carriers into reference and rapid acetylators. Rapid NAT1 acetylator status seems to protect against SMX toxicity by compensating for slow NAT2 acetylator status.

Lower risk of urinary tract infection with low-dose trimethoprim/sulfamethoxazole compared to dapsone prophylaxis in older renal transplant patients on a rapid steroid-withdrawal immunosuppression regimen

BACKGROUND

Urinary tract infections (UTI) are common in renal transplant recipients. Trimethoprim/sulfamethoxazole (TMP/SMZ) in moderate to high daily doses prevents Pneumocystis jiroveci (PCP) and reduces the risk of UTI in renal transplant patients. Low-dose TMP/SMZ also reduces the risk of PCP, although its ability to reduce the risk of UTI is uncertain.

DESIGN

Retrospective review of 158 patients who received a renal transplant without corticosteroids for maintenance immunosuppression.

RESULTS

Forty percent of patients initially prescribed TMP/SMZ ultimately stopped this medication early because of an adverse reaction. Urinary infection occurred in 16% without a significant difference in the risk of UTI between those treated with dapsone vs. those treated with TMP/SMZ (HR [95%CI]: 1.7 [0.75, 3.9], p = 0.2). In the subset of patients who were older than age 47 yr (mean age for this cohort, SD ± 6.2 yr), those treated with dapsone originally or who switched from TMP/SMZ to dapsone had a greater risk of UTI compared to patients who remained on TMP/SMZ (HR [95%CI]: 4.3 [1.2, 15.5], p = 0.024).

CONCLUSIONS

For renal transplant recipients over the age of 47 yr, treated without long-term glucocorticoids, our retrospective data suggest that low-dose TMP/SMZ is associated with a lower risk of UTI compared to dapsone prophylaxis.

Adverse antibiotic-induced eruptions associated with epstein barr virus infection and showing Kikuchi-Fujimoto disease-like histology

The antibiotic-induced eruption of infectious mononucleosis is a well-known clinical phenomenon. Latent viral infection with herpesviridae (eg, human herpes virus 6 (HHV-6) and Epstein-Barr virus (EBV)) is suspected to play a role in the drug hypersensitivity syndrome. The cutaneous pathologic findings have not been reported in the former, and are infrequently reported in the latter entity. Herein, we describe the biopsy findings of a cefprozil-induced rash in infectious mononucleosis and a minocycline-associated drug hypersensitivity syndrome. Biopsy of these exanthematous eruptions revealed an acute vacuolar interface superficial and deep perivascular and interstitial lymphocytic dermatitis. CD8(+) lymphocytes predominated and were associated with non-neutrophilic nuclear (karyorrhectic) debris and numerous small CD68(+) and CD123(+) monocytes. These aforementioned features have been described in cutaneous lesions of Kikuchi-Fujimoto disease, an entity whose clinicopathologic findings overlap with both infectious mononucleosis and lupus erythematosus. Serologic evidence of active and chronic active EBV infection was found in both patients, respectively. No evidence of EBV or HHV6 was found in the cutaneous lesions. Plasmacytoid monocytes (CD68(+)/CD123(+) cells), which produce type I interferon, are believed to play a role in viral immunity by protecting other cells from viral infections and promoting survival of antigen-activated T cells. Their presence in these two putative examples of viral-drug immune dysregulation could be a clue to pathogenesis and represent a common cellular component of some adverse cutaneous drug eruptions.

Prevention of infection due to Pneumocystis spp. in human immunodeficiency virus-negative immunocompromised patients

Pneumocystis infection in humans was originally described in 1942. The organism was initially thought to be a protozoan, but more recent data suggest that it is more closely related to the fungi. Patients with cellular immune deficiencies are at risk for the development of symptomatic Pneumocystis infection. Populations at risk also include patients with hematologic and nonhematologic malignancies, hematopoietic stem cell transplant recipients, solid-organ recipients, and patients receiving immunosuppressive therapies for connective tissue disorders and vasculitides. Trimethoprim-sulfamethoxazole is the agent of choice for prophylaxis against Pneumocystis unless a clear contraindication is identified. Other options include pentamidine, dapsone, dapsone-pyrimethamine, and atovaquone. The risk for PCP varies based on individual immune defects, regional differences, and immunosuppressive regimens. Prophylactic strategies must be linked to an ongoing assessment of the patient's risk for disease.

Opportunistic infections in patients with and patients without Acquired Immunodeficiency Syndrome

In the next decade, longer survival of patients with cancer and more-aggressive therapies applied to common conditions, such as asthma and rheumatoid arthritis, will result in a larger population with significant immune system defects. Many in this population will be at risk for opportunistic infections, which are familiar to doctors who have treated people infected with human immunodeficiency virus (HIV). However, the epidemiology, presentation, and outcome of these infections in patients with an immune system defect, other than that caused by HIV infection, may be different than those encountered in patients with acquired immunodeficiency syndrome. Reviewed are 4 common opportunistic infections: Pneumocystis carinii pneumonia, cryptococcosis, atypical mycobacterial infection, and cytomegalovirus infection. Emphasized are the important differences among these groups at risk.

Allergic adverse reactions to sulfonamides

Antimicrobial sulfonamides were the first antimicrobial agents used effectively to treat infectious diseases. However, because they may cause severe adverse drug reactions (ADRs) and because more effective agents have since been developed, sulfonamides now are used for only a few indications in specific groups, such as AIDS patients. Skin reactions, from benign rash to potentially lethal toxidermias, are the most frequent ADRs to sulfonamides. Other major ADRs include acute liver injury, pulmonary reactions, and blood dyscrasias. Although the mechanisms involved have not been fully elucidated, reactive metabolites appear to play a pivotal role. The hydroxylamine and nitroso metabolites of sulfamethoxazole, the most frequently used sulfonamide today, can bind covalently to proteins because of their chemical reactivity, resulting in the induction of specific adverse immune responses. Therefore, changes in the activity of metabolic and detoxification pathways are associated with a greater risk for developing allergic reactions to sulfonamides. Allergies to sulfonamides, particularly sulfamethoxazole (often used in combination with trimethoprim as co-trimoxazole), are more frequent in AIDS patients, but the reason for this increased risk is not fully understood. No valid tools are available to predict which patients have a greater risk for developing allergies to sulfonamides. Diagnosis is essential to avoid a possible evolution toward severe reactions and readministration of the offending drug. In patients who absolutely require further treatment, successful desensitization may be achieved.