Dapsone-associated methemoglobinemia in a patient with slow NAT2*5B haplotype and impaired cytochrome b5 reductase activity

Cutaneous Lupus Erythematosus: Review and Considerations for Older Populations

Though more common earlier in life, increasing attention is being focused on the development of cutaneous lupus erythematosus (CLE) in patients with advancing age. Studies show that CLE is more common in older populations than previously thought, and all CLE subtypes are possible in this group. Just like patients in the third or fourth decade of life, CLE may appear alongside or independent of systemic lupus erythematosus. Older populations manifesting CLE for the first time seem to have a lower risk of progression to systemic disease than younger peers, and are more commonly White. CLE must be carefully distinguished from other skin conditions that have a predilection for presentation in older populations, including rosacea, lichen planus, and other autoimmune conditions such as dermatomyositis or pemphigus/pemphigoid. It is thought that most CLE in older populations is drug-induced, with drug-induced subacute cutaneous lupus erythematosus being the most common subtype. Management of CLE in older patients focuses on eliminating unnecessary medications known to induce CLE, and otherwise treatment proceeds similarly to that in younger patients, with a few special considerations.

Case Study 10: A Case to Investigate Acetyl Transferase Kinetics

Major routes of metabolism for marketed drugs are predominately driven by enzyme families such as cytochromes P450 and UDP-glucuronosyltransferases. Less studied conjugative enzymes, like N-acetyltransferases (NATs), are commonly associated with detoxification pathways. However, in the clinic, the high occurrence of NAT polymorphism that leads to slow and fast acetylator phenotypes in patient populations has been linked to toxicity for a multitude of drugs. A key example of this is the observed clinical toxicity in patients who exhibit the slow acetylator phenotype and were treated with isoniazid. Toxicity in patients has led to detailed characterization of the two NAT isoforms and their polymorphic genotypes. Investigation in recombinant enzymes, genotyped hepatocytes, and in vivo transgenic models coupled with acetylator status-driven clinical studies have helped understand the role of NATs in drug development, clinical study design and outcomes, and potential roles in human disease models. The selected case studies herein document NAT enzyme kinetics to explore substrate overlap from two human isoforms, preclinical species considerations, and clinical genotype population concerns.

Dapsone for Pneumocystis jirovecii pneumonia prophylaxis - applying theory to clinical practice with a focus on drug interactions

Pneumocystis jirovecii pneumonia (PJP) is a potentially life-threatening infection that occurs in immunocompromised individuals. The incidence can be as high as 80% in some groups but can be reduced to less than 1% with appropriate prophylaxis. HIV-infected patients with a low CD4 count are at the highest risk of PJP. Others at substantial risk include haematopoietic stem cell and solid organ transplant recipients, those with cancer (particularly haematologic malignancies), and those receiving glucocorticoids, chemotherapeutic agents, and other immunosuppressive medications. Trimethoprim-sulfamethoxazole is an established first-line line agent for prevention and treatment of PJP. However, in some situations, this medication cannot be used and dapsone is considered a suitable cost-effective second line agent. However, information on potential interactions with drugs commonly used in immunosuppressed patients is lacking or contradictory. In this this article we review the metabolic pathway of dapsone with a focus on interactions and clinical significance particularly in patients with haematological malignancies. An understanding of this process should optimise the use of this agent.

Dapsone and azole interactions: A clinical perspective

An understanding of the clinical significance of dapsone-drug interactions is essential for optimal use of this agent. This review aims to provide clinicians with an overview of this topic.

Immunogenicity of trimethoprim/sulfamethoxazole in a macaque model of HIV infection

BACKGROUND

Sulfonamide hypersensitivity has a high incidence in HIV infection and correlates with low CD4+ counts, but the mechanisms are not understood. The aims of this study were to determine whether trimethoprim/sulfamethoxazole (TMP/SMX) led to SMX adduct formation, immunogenicity, or signs of drug hypersensitivity in SIV-infected rhesus macaques, and whether differences in antioxidants, pro-inflammatory mediators, or SMX disposition were predictive of drug immunogenicity.

METHODS

Nine macaques chronically infected with SIVmac239 and 7 non-infected controls were studied. Baseline blood ascorbate, glutathione, IFN-γ, LPS, sCD14, and cytochrome b₅ reductase measurements were obtained, macaques were dosed with TMP/SMX (120mg/kg/day p.o. for 14days), and SMX metabolites, lymph node drug adducts, drug-responsive T cells, and anti-SMX antibodies were measured.

RESULTS

Four of 9 of SIV-positive (44%), and 3 of 7 SIV negative (43%) macaques had drug-responsive T cells or antibodies to SMX. Two macaques developed facial or truncal rash; these animals had the highest levels of lymph node drug adducts. Antioxidants, pro-inflammatory mediators, and SMX metabolites were not predictive of drug immunogenicity; however, the Mamu DRB1*0401/0406/0411 genotype was significantly over-represented in immune responders.

CONCLUSIONS

Unlike other animal models, macaques develop an immune response, and possible rash, in response to therapeutic dosages of TMP/SMX. Studying more animals with CD4+ counts <200cells/μl, along with moderately restricted ascorbate intake to match deficiencies seen in humans, may better model the risk of SMX hypersensitivity in HIV-infection. In addition, the role of Mamu-DRB1 genotype in modeling drug hypersensitivity in retroviral infection deserves further study.

Dapsone-induced methemoglobinemia in renal transplant recipients: more prevalent than previously thought

BACKGROUND

After an outbreak of Pneumocystis pneumonia (PCP) in our nephrology unit, dapsone was used as the second-line chemoprophylactic agent. Dapsone is the most common cause of drug-induced methemoglobinemia (MHb). Its prevalence is poorly described in the renal transplant population. Because dapsone is excreted by the kidneys, we hypothesized that the rate of MHb in these patients would be higher than previously reported. We aimed to describe the demographics, risk factors, and presenting features of MHb in these renal transplant patients.

METHODS

Twenty-six transplant recipients commenced on dapsone for chemoprophylaxis against PCP from February to September 2011. All patients had normal glucose-6-phosphate dehydrogenase levels before treatment. Characteristics of patients with MHb were compared with those of the rest of the cohort to determine potential risk factors.

RESULTS

Twelve (46%) patients developed MHb (levels 6.4 ± 4.1%). Six (50%) of the patients with MHb were asymptomatic on presentation. Cases had a mean drop in hemoglobin of 19 ± 7%. MHb led to five admissions (median length of stay 5 days, range 1-10 days). MHb level showed a strong correlation with the length of stay (correlation coefficient 0.762, P = 0.002).

CONCLUSION

This is the highest reported prevalence of MHb, to our knowledge, in patients receiving dapsone, and its use led to significant hospitalization in this population. This study raises concerns about the use of dapsone as chemoprophylaxis in renal transplant recipients.

Methemoglobinemia induced by trimethoprim-sulfamethoxazole in a patient with systemic lupus erythematosus

We herein report a case of methemoglobinemia induced by trimethoprim-sulfamethoxazole (TMP/SMX). A 41-year-old woman with systemic lupus erythematosus (SLE) received TMP/SMX for prophylaxis of pneumocystis pneumonia (PCP) on the 7th day of hospitalization. She suddenly developed dyspnea and cyanosis on the 9th day of hospitalization. The level of oxygen saturation (SaO2) decreased, and the concentration of methemoglobin (MetHb) in the blood was elevated. We diagnosed the patient with methemoglobinemia induced by TMP/SMX. Methemoglobinemia should be considered in cases of sudden dyspnea following TMP/SMX administration.