Dapsone treatment of Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome

A Review of Pneumocystis Pneumonia

Pneumocystis pneumonia remains one of the leading causes of morbidity and mortality in the HIV-infected population. Trimethoprim-sulfamethoxazole remains the drug of choice for both the treatment and prevention of this infection, although a high rate of side effects in HIV-infected patients often necessitates alternative treatment regimens. This article will review pneumocystis pneumonia, with a focus on the various therapeutic options, their side effects, and the immune reconstitution inflammatory syndrome as it relates to pneumocystis pneumonia infection.

L-arginine, a nitric oxide precursor, reduces dapsone-induced methemoglobinemia in rats

Dapsone use is frequently associated to hematological side effects such as methemoglobinemia and hemolytic anemia, which are related to N-hydroxylation mediated by the P450 enzyme system. The aim of the present study was to evaluate the influence of L-arginine supplementation, a precursor for the synthesis of nitric oxide, as single or multiple dose regimens on dapsone-induced methemoglobinemia. Male Wistar rats were treated with L-arginine at 5, 15, 30, 60 and 180 mg/kg doses (p.o., gavage) in single or multiple dose regimens 2 hours prior to dapsone administration (40 mg/kg, i.p.). The effect of the nitric oxide synthase inhibitor L-NAME was investigated by treatment with multiple doses of 30 mg/kg (p.o., gavage) 2 hours before dapsone administration. Blood samples were collected 2 hours after dapsone administration. Erythrocytic methemoglobin levels were assayed by spectrophotometry. The results showed that multiple dose supplementations with 5 and 15 mg/kg L-arginine reduced dapsone-induced methemoglobin levels. This effect is mediated by nitric oxide formation, since the reduction in methemoglobin levels by L-arginine is blocked by simultaneous administration with L-NAME, a nitric oxide synthase inhibitor.

Guidelines for the Prevention and Treatment of Opportunistic Infections among HIV-exposed and HIV-infected children: recommendations from CDC, the National Institutes of Health, the HIV Medicine Association of the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, and the American Academy of Pediatrics

This report updates and combines into one document earlier versions of guidelines for preventing and treating opportunistic infections (OIs) among HIV-exposed and HIV-infected children, last published in 2002 and 2004, respectively. These guidelines are intended for use by clinicians and other health-care workers providing medical care for HIV-exposed and HIV-infected children in the United States. The guidelines discuss opportunistic pathogens that occur in the United States and one that might be acquired during international travel (i.e., malaria). Topic areas covered for each OI include a brief description of the epidemiology, clinical presentation, and diagnosis of the OI in children; prevention of exposure; prevention of disease by chemoprophylaxis and/or vaccination; discontinuation of primary prophylaxis after immune reconstitution; treatment of disease; monitoring for adverse effects during treatment; management of treatment failure; prevention of disease recurrence; and discontinuation of secondary prophylaxis after immune reconstitution. A separate document about preventing and treating of OIs among HIV-infected adults and postpubertal adolescents (Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents) was prepared by a working group of adult HIV and infectious disease specialists. The guidelines were developed by a panel of specialists in pediatric HIV infection and infectious diseases (the Pediatric Opportunistic Infections Working Group) from the U.S. government and academic institutions. For each OI, a pediatric specialist with content-matter expertise reviewed the literature for new information since the last guidelines were published; they then proposed revised recommendations at a meeting at the National Institutes of Health (NIH) in June 2007. After these presentations and discussions, the guidelines underwent further revision, with review and approval by the Working Group, and final endorsement by NIH, CDC, the HIV Medicine Association (HIVMA) of the Infectious Diseases Society of America (IDSA), the Pediatric Infectious Disease Society (PIDS), and the American Academy of Pediatrics (AAP). The recommendations are rated by a letter that indicates the strength of the recommendation and a Roman numeral that indicates the quality of the evidence supporting the recommendation so readers can ascertain how best to apply the recommendations in their practice environments. An important mode of acquisition of OIs, as well as HIV infection among children, is from their infected mother; HIV-infected women coinfected with opportunistic pathogens might be more likely than women without HIV infection to transmit these infections to their infants. In addition, HIV-infected women or HIV-infected family members coinfected with certain opportunistic pathogens might be more likely to transmit these infections horizontally to their children, resulting in increased likelihood of primary acquisition of such infections in the young child. Therefore, infections with opportunistic pathogens might affect not just HIV-infected infants but also HIV-exposed but uninfected infants who become infected by the pathogen because of transmission from HIV-infected mothers or family members with coinfections. These guidelines for treating OIs in children therefore consider treatment of infections among all children, both HIV-infected and uninfected, born to HIV-infected women. Additionally, HIV infection is increasingly seen among adolescents with perinatal infection now surviving into their teens and among youth with behaviorally acquired HIV infection. Although guidelines for postpubertal adolescents can be found in the adult OI guidelines, drug pharmacokinetics and response to treatment may differ for younger prepubertal or pubertal adolescents. Therefore, these guidelines also apply to treatment of HIV-infected youth who have not yet completed pubertal development. Major changes in the guidelines include 1) greater emphasis on the importance of antiretroviral therapy for preventing and treating OIs, especially those OIs for which no specific therapy exists; 2) information about the diagnosis and management of immune reconstitution inflammatory syndromes; 3) information about managing antiretroviral therapy in children with OIs, including potential drug--drug interactions; 4) new guidance on diagnosing of HIV infection and presumptively excluding HIV infection in infants that affect the need for initiation of prophylaxis to prevent Pneumocystis jirovecii pneumonia (PCP) in neonates; 5) updated immunization recommendations for HIV-exposed and HIV-infected children, including hepatitis A, human papillomavirus, meningococcal, and rotavirus vaccines; 6) addition of sections on aspergillosis; bartonella; human herpes virus-6, -7, and -8; malaria; and progressive multifocal leukodystrophy (PML); and 7) new recommendations on discontinuation of OI prophylaxis after immune reconstitution in children. The report includes six tables pertinent to preventing and treating OIs in children and two figures describing immunization recommendations for children aged 0--6 years and 7--18 years. Because treatment of OIs is an evolving science, and availability of new agents or clinical data on existing agents might change therapeutic options and preferences, these recommendations will be periodically updated and will be available at http://AIDSInfo.nih.gov.

Pneumocystis jiroveci Pneumonia in Adult Patients with AIDS

Pneumocystis jiroveci (P. carinii) is an opportunistic pathogen that has gained particular prominence since the onset of the AIDS epidemic. Among several important advances in diagnosis and management, appropriately targeting chemoprophylaxis to HIV-infected patients at high clinical risk for P. jiroveci pneumonia and the introduction of effective combination anti-retroviral therapy (including highly active antiretroviral therapy [HAART]) have contributed to the reduced incidence of P. jiroveci pneumonia. Despite the success of these clinical interventions, P. jiroveci pneumonia remains the most common opportunistic pneumonia and the most common life-threatening infectious complication in HIV-infected patients. Trimethoprim/sulfamethoxazole (cotrimoxazole) remains the first-line agent for effective therapy and chemoprophylaxis, and corticosteroids represent an important adjunctive agent in the treatment of moderate-to-severe P. jiroveci pneumonia. However, problems of chemoprophylaxis and treatment failures, high rates of adverse drug reactions and drug intolerance to first-line antimicrobials, high rates of relapse or recurrence with second-line agents, and newer concerns about the development of P. jiroveci drug resistance represent formidable challenges to the management and treatment of AIDS-related P. jiroveci pneumonia. With the expanding global problem of HIV infection, the intolerance or unavailability of HAART to many individuals and limited access to healthcare for HIV-infected patients, P. jiroveci pneumonia will remain a major worldwide problem in the HIV-infected population. New drugs under development as anti-Pneumocystis agents such as echinocandins and pneumocandins, which inhibit beta-glucan synthesis, or sordarins, which inhibit fungal protein synthesis, show promise as effective agents. Continued basic research into the biology and genetics of P. jiroveci and host defense response to P. jiroveci will allow the development of newer antimicrobials and immunomodulatory therapeutic agents to more effectively treat life-threatening pneumonia caused by this organism.

Pneumocystis carinii pneumonia in patients with and without HIV infection

Advances in the prevention and treatment of Pneumocystis carinii pneumonia in HIV infected patients have led to a decrease in the incidence and improved outcomes. Pneumocystis carinii pneumonia continues to be problematic in non-HIV infected immunocompromised patients.

Pneumonia in AIDS patients in the critical care unit

Despite advances in prophylaxis and the reduction of mortality and morbidity resulting from highly active antiretroviral therapy, neumocystis pneumonia remains a common problem in HIV-infected patients. There are many possible causes for the continued prevalence of this condition. This article examines the characteristics, and some of the complex causes of P. carinii pneumonia in AIDS patients.

Pneumocystis carinii pneumonia

Pneumocystis carinii pneumonia (PCP) remains an important complication of AIDS. Advances have been made in establishing the taxonomy of the organism but the life cycle of the organism and pathogenetic mechanisms of disease remain obscure. In HIV patients the incidence of PCP has decreased because of widespread use of prophylaxis and survival of those with PCP has improved with use of adjunctive corticosteroid therapy. Less toxic drug therapies are still needed as well as better noninvasive diagnostic techniques.

AIDS and the lung

Respiratory symptoms are common in HIV-infected persons. The challenge facing clinicians is to determine whether these respiratory symptoms are due to an opportunistic infection or to a chronic process, such as asthma, chronic bronchitis, bronchiectasis, or emphysema. This article reviewed the clinical presentation, diagnosis, and treatment of two important opportunistic infections, PCP and bacterial pneumonia. It also reviewed the current data on obstructive lung diseases as they relate to HIV.

Therapeutic progress. IV: Treatment and prophylaxis of Pneumocystis carinii infection

Co-trimoxazole presently remains the first choice for prophylaxis and treatment of Pneumocystis carinii infections. The high incidence of adverse reactions experienced by patients taking co-trimoxazole has led to a number of trials comparing it with other antipneumocystis agents. Adjuvant therapy with corticosteroids may benefit patients with severe P. carinii pneumonia. This paper reviews the standard treatments for P. carinii pneumonia, some of the newer agents such as atovaquone, recently licensed in the U.K., and a variety of novel agents being assessed for treatment and prophylaxis. Current recommendations may change over the new few years.

Hyperkalemia and high-dose trimethoprim/sulfamethoxazole

Evidence from the literature strongly supports that high doses of TMP, as used in the treatment of PCP in AIDS patients, have the propensity to cause hyperkalemia by inhibiting sodium channels in the distal nephron, thereby impairing potassium secretion. The mechanism of TMP-induced hyperkalemia is believed to be similar to that of triamterene and amiloride because of the structural similarity of these agents. It is also possible that declining renal function, which is a natural progression of HIV disease, may contribute to the hyperkalemia seen in this patient population. In addition, patients with AIDS also may exhibit a defect in adrenal function, potentiating the hyperkalemic effect of TMP therapy. Therefore, it is crucial for clinicians to monitor closely the serum potassium concentration in this patient population, especially during therapy with high doses of TMP.

Evaluation of effects of altered gastric pH on absorption of dapsone in healthy volunteers

A prospective, randomized, crossover study was performed with seven healthy volunteers to address the effect of increased gastric pH on dapsone absorption. Subjects were randomized to receive a single 100-mg dose of dapsone or a single 100-mg dose of dapsone in addition to 30 ml of a high potency antacid 1 h before dapsone administration and hourly thereafter for a total of 10 doses. Dapsone concentrations in serum were measured periodically for 48 h. No statistical differences between the two regimens were noted when mean dapsone maximal initial concentrations, times to peak, and areas under the curve were compared. These data suggest that an increase in gastric pH has little or no effect on the absorption of dapsone in healthy subjects.

Adverse effects of drugs used in the management of opportunistic infections associated with HIV infection

Pneumocystis carinii pneumonia (PCP) is one of the most common AIDS-defining diagnoses. First-line therapy is cotrimoxazole (trimethoprim-sulfamethoxazole), despite a high incidence of toxic effects, and a greater incidence of hypersensitivity reactions among HIV-positive patients compared with the seronegative population. Alternative agents such as intravenous pentamidine, or clindamycin with primaquine, and trimethoprim with dapsone, also have a wide range of serious adverse effects, but remain treatment options. Atovaquone appears promising for the treatment of both PCP and toxoplasmosis, and has a lower reported incidence of toxicity than the alternative agents. The most toxic antifungal drugs are reserved for serious infections, such as cryptococcal meningitis. Liposomal amphotericin B has less renal toxicity than standard formulations, and exemplifies that new formulations of existing drugs, although often expensive, may have a better adverse effect profile. There are 2 different drugs currently available for cytomegalovirus (CMV) infections, ganciclovir and foscarnet. Both have a high incidence of serious adverse effects; ganciclovir mainly causes bone marrow toxicity and foscarnet leads to renal toxicity. The drugs used for mycobacterial infection (including mycobacteria as well as tuberculosis) have a wide range of adverse effects, particularly skin rashes and drug-induced hepatitis. Some of these compounds are quite new, such as rifabutin and clarithromycin, and it is important to be ever vigilant for previously unreported adverse effects.

Randomized trial of dapsone and aerosolized pentamidine for the prophylaxis of Pneumocystis carinii pneumonia and toxoplasmic encephalitis

PURPOSE

Pneumocystis carinii pneumonia (PCP) and toxoplasmic encephalitis are the most frequent pulmonary and central nervous system opportunistic infections associated with human immunodeficiency virus (HIV) infection. We designed a prospective study to compare the effects of aerosolized pentamidine and dapsone in the prophylaxis of these infections in HIV-infected persons with CD4+ lymphocyte counts less than 250/mm3.

PATIENTS AND METHODS

Two hundred seventy-eight patients seropositive for HIV who had acquired immunodeficiency syndrome (AIDS) or advanced AIDS-related complex were randomly assigned to receive intermittent dapsone (100 mg twice weekly) or aerosolized pentamidine (100 mg every 2 weeks). The proportion of patients remaining free of PCP or toxoplasmosis was analyzed with the log-rank test as a function of time, as were the effects of zidovudine or prophylaxis on survival.

RESULTS

Dapsone and aerosolized pentamidine demonstrated similar efficacy in the primary and secondary prophylaxis of PCP, with 15 (18%) failures among patients receiving dapsone compared to 15 (14%) among those receiving aerosolized pentamidine (p = 0.4), after a mean length of follow-up of 42 and 44 weeks, respectively. Dapsone was more effective in the primary prophylaxis of toxoplasmic encephalitis, with six toxoplasmic encephalitis events occurring among those receiving aerosolized pentamidine, compared to none among those taking dapsone (p = 0.01). Primary prophylaxis for PCP was more effective than secondary prophylaxis with either therapy. Zidovudine therapy did not prevent PCP yet prolonged the PCP-free interval for those in whom either prophylactic therapy failed. Kaplan-Meier estimates did not show a difference in survival between the patients receiving either therapy, yet zidovudine use was associated with improved survival, independent of race and risk factor (Cox proportional hazards model, p = 0.001). The 1-month survival for patients developing PCP despite prophylaxis was better with those in whom dapsone failed than it was for those in whom aerosolized pentamidine failed (p = 0.08).

CONCLUSION

Dapsone is as effective as aerosolized pentamidine in preventing PCP and has the advantage of a lower cost, easier administration, and possibly an additional preventive effect against toxoplasmosis. Zidovudine prolongs the PCP-free interval for patients receiving prophylaxis, regardless of which prophylactic agent is used.

Pneumocystis carinii pneumonia in cancer patients

Concern has been arisen about the recently reported increasing incidence of PCP in patients with cancer and the potential transmissibility of this infection. Whether or not there is an increase in the incidence of P. carinii infections, PCP should be considered in the differential diagnosis of pulmonary infiltrates in bone marrow transplant recipients, in patients with hematologic neoplasms and in patients with primary or metastatic brain neoplasms. Intensity of immunosuppression plays a crucial role, especially long-term (> 2 months) corticosteroid treatment. PCP is usually manifested clinically during augmentation or during tapering of corticosteroid dose. Thus, if the chest radiograph of a high-risk patient shows diffuse infiltrates, bronchoscopy and bronchoalveolar lavage should be done immediately. Treatment options are the same as for the AIDS population, except that TMP-SMX is tolerated better in non-AIDS patients. The role of supportive care, including mechanical ventilation in such patients should not be underestimated. Oral therapy with dapsone-trimethoprim or with atovaquone, can be as effective as conventional therapy in mild disease, permitting treatment on an outpatient basis. PCP is often preventable and our understanding has improved about when prophylaxis should be initiated. In the future, the emergence of new technologies for diagnosis and of new agents for treatment and prophylaxis, will bring us closer to the goal of controlling this serious infection.

Synergistic combinations of Ro 11-8958 and other dihydrofolate reductase inhibitors with sulfamethoxazole and dapsone for therapy of experimental pneumocystosis

We compared Ro 11-8958, an analog of trimethoprim (TMP) with improved antimicrobial and pharmacokinetic properties, other dihydrofolate reductase (DHFR) inhibitors, sulfamethoxazole (SMX), and dapsone (DAP) in the treatment of Pneumocystis carinii pneumonia in an immunosuppressed rat model. In contrast to previous reports, high dosages of the DHFR inhibitors were used in combination with fixed, low dosages of SMX (3 mg/kg of body weight per day) or DAP (25 mg/kg/day). When administered alone at these dosages, SMX and DAP reduced the median P. carinii cyst count about 5- to 15-fold. Ro 11-8958, TMP, and diaveridine used at a dosage of 20 mg/kg/day with SMX were only slightly more effective than SMX used alone. However, administration of these DHFR inhibitors at a dosage of 100 mg/kg/day with SMX lowered the cyst count about 500- to 1,000-fold, indicating a synergistic effect. Little or no synergism was found when other DHFR inhibitors (pyrimethamine, cycloguanil, and tetroxoprim) were combined with SMX. Regimens of Ro 11-8958 at a dosage of 20 mg/kg/day with DAP and of TMP or diaveridine used at a dosage of 100 mg/kg/day with DAP showed comparable anti-P. carinii activity, lowering the cyst count 100- to 200-fold. By contrast, Ro 11-8958 administered at a dosage of 100 mg/kg/day with DAP reduced the cyst count > 1,000-fold. Thus, the experimental approach used here enables the rat model of pneumocystosis to be used to compare synergistic combinations of antifolate drugs. The favorable results achieved with Ro 11-8958 indicate that it should be considered for clinical trials.

Pharmacokinetic optimisation in the treatment of Pneumocystis carinii pneumonia

Several drugs and drug combinations are currently used in the treatment of patients with Pneumocystis carinii pneumonia (PCP)--pentamidine and cotrimoxazole (trimethoprim plus sulphamethoxazole), which are indicated for this usage, dapsone/trimethoprim and clindamycin/primaquine, which are not licensed for PCP, and trimetrexate/calcium folinate (leucovorin), eflornithine and BW-566C (566 C80) as investigational drugs. For most of these agents, recommendations regarding the use of pharmacokinetic parameters to establish individualised therapy cannot be made. The pharmacokinetics of antipneumocystis drugs are not well documented and clinical trials evaluating the relationship between the individual plasma pharmacokinetic profiles and responses to treatment are sparse. In clinical trials, the reduction of the daily dose of pentamidine to 3 or 2 mg/kg/day and of cotrimoxazole to 15 mg/kg of the trimethoprim component resulted in a substantial reduction of frequency and severity of adverse drug effects without diminishing efficacy. For pentamidine, a long half-life of > or = 4 days implies the need for a loading dose. Plasma concentrations of the parent drug at steady-state varied between 30 and 100 micrograms/L. The elimination pharmacokinetics are characterised by several elimination slopes indicating the existence of a deep peripheral compartment. Due to its very low renal clearance, dosage adjustments are not necessary in patients with renal impairment. The pharmacokinetics of cotrimoxazole follow first-order kinetics in PCP and the particular parameters are similar to those reported in the treatment of bacterial infection. Steady-state plasma concentrations of both trimethoprim and sulphamethoxazole are attained within 2 to 3 days, but the range of 'therapeutic' plasma concentrations must be newly defined, since elevated trimethoprim concentrations could not be correlated with the frequency and severity of adverse drug reactions. The concentrations of sulphamethoxazole may be at least as important as those of trimethoprim in defining a toxic range. With dapsone/trimethoprim, clindamycin/primaquine and BW-566C (566 C 80) good clinical response rates were found in groups of patients with mild to moderate PCP. Comparative trials with standard drugs are still ongoing. Therapeutic to toxic concentration ratios have not been established in patients with PCP. Pharmacokinetic data pertaining to patients with PCP are either nonexistent or incomplete, or are complicated by a drug interaction between dapsone and trimethoprim suggesting an inhibition of metabolism of dapsone. Eflornithine and trimetrexate/calcium folinate have been used under specific research protocols, showing partial success as salvage agents for desperately ill patients with AIDS. Regarding all antipneumocystis drugs, additional clinical and pharmacokinetic data are needed to optimise and more fully individualise the treatment regimens for this severe infection.

Efficacy of ganciclovir in combination with other antimicrobial agents against cytomegalovirus in vitro and in vivo

In MRC-5 cell cultures, the efficacy of the acyclic nucleoside ganciclovir (GCV) against human cytomegalovirus (CMV) was unaffected when combined with either amphotericin B (AMP B), ketoconazole (KCZ), dapsone (DAP), or trimethoprim/sulfamethoxazole (TMP/SMX). When differences in 3-dimensional plots for antiviral activity and cytotoxicity of GCV alone and in combination were compared, the anti-CMV activity of GCV (IC50 8 microM, 5-9 microM range) was not affected by concentrations of up to 10 microM AMP B, 1000 microM KCZ, 100 microM DAP or 320 microM TMP/SMX (higher concentrations could not be tested due to cytotoxicity). In Swiss Webster mice, the anti-CMV activity of GCV was also unaffected when administered in combination with any of the four other antimicrobial agents against murine CMV. GCV (s.c.) alone had an ED50 of 7 mg/kg (2-12 mg/kg range) which was unaffected by daily doses of 1 mg/kg AMP B (i.p.), 60 mg/kg KCZ (i.p.), 32 mg/kg DAP (p.o.) or 80/400 mg/kg TMP/SMX (p.o.). These results suggest that GCV can be administered in combination with these other drugs for treatment of various opportunistic infections in AIDS patients without compromising the efficacy of GCV against CMV.

Inhibition of dapsone-induced methaemoglobinaemia by cimetidine in the presence of trimethoprim in the rat

Administration of dapsone in combination with trimethoprim and cimetidine to male rats resulted in a marked decrease (P less than 0.05) in measured methaemoglobin levels (46.2 +/- 24% Met Hb h) compared with administration of dapsone alone (124.5 +/- 24.4% Met Hb h). The elimination half-life of dapsone (814 +/- 351 min) was more than doubled in the presence of trimethoprim and cimetidine compared with control (355 +/- 160 min, P less than 0.05). However, there were no significant differences in AUC and clearance when dapsone was administered in combination with trimethoprim and cimetidine compared with dapsone alone. Co-administration of trimethoprim with dapsone in the absence of cimetidine did not affect either methaemoglobin formation, AUCs, half-lives, or clearance values of dapsone compared with control. There was a threefold increase in the AUC of trimethoprim (6296 +/- 2249 micrograms min mL-1) in the presence of dapsone compared with trimethoprim alone (2122 +/- 552 micrograms min mL-1). There was also a corresponding decrease in the clearance of trimethoprim in the presence of dapsone compared with control (19.1 +/- 6.9 vs 60.8 +/- 21.0 mL min-1). However, there was no change in the elimination half-life of trimethoprim between the two experimental groups (273 +/- 120 vs 292 +/- 54 min). The AUC of trimethoprim increased more than threefold in the presence of cimetidine (7100 +/- 1501 micrograms min mL-1) compared with trimethoprim alone (2122 +/- 552 micrograms min mL-1).(ABSTRACT TRUNCATED AT 250 WORDS)

New developments in the treatment of Pneumocystis carinii pneumonia

Pneumocystis carinii pneumonia and therapies to treat this infection are associated with frequent and severe morbidity in patients with acquired immunodeficiency syndrome (AIDS). Mortality rates remain in the 20 to 40 percent range for severe episodes. Thus, less toxic and more effective therapies are needed. For mild-to-moderately severe episodes (PaO2 greater than 70 mm Hg or [A-a]DO2 less than 35 mm Hg), studies suggest that trimethoprim-dapsone, clindamycin-primaquine, and BW 566C80 may cause less toxicity than conventional therapy with trimethoprim-sulfamethoxazole or parenteral pentamidine. However, prospective, controlled trials are needed to establish whether the newer therapies are as effective as the existing licensed treatments. Aerosolized pentamidine is another new therapy that is better tolerated than trimethoprim-sulfamethoxazole but may not be as effective as parenteral treatment when there is extensive airspace consolidation. For severe episodes (PaO2 less than 70 mm Hg or [A-a]DO2 greater than 35 mm Hg), recent studies have established that adjunctive therapy with corticosteroids reduces mortality approximately twofold. For patients who have failed conventional treatments and are unable to ingest oral medications, trimetrexate may be tried. Other compounds being tested may further expand the therapeutic armamentarium with safer and more effective drugs.

Anti-Toxoplasma effects of dapsone alone and combined with pyrimethamine

The efficacy of dapsone alone or combined with pyrimethamine against Toxoplasma gondii was investigated experimentally. For in vitro studies, a sensitive immunoassay was used for assessment of Toxoplasma growth in tissue cultures; dapsone was found to have a significant inhibitory effect at a concentration of 0.5 micrograms/ml in the cultures, and the 50% inhibitory concentration was estimated to be 0.55 micrograms/ml. When pyrimethamine and dapsone were combined, an important synergistic effect which was associated with morphological alterations of the parasites was observed. In vivo studies were performed in a murine model of acute toxoplasmosis in which a tissue culture method was used to estimate the parasite burden in the blood, lungs, and brains of infected mice. Dapsone alone, which was administered at 100 mg/kg/day for 10 days from day 1 after infection, was unable to prevent parasite dissemination and only delayed the time to death of treated mice compared with the time of death of untreated controls. When dapsone and pyrimethamine (18.5 mg/kg/day) were administered in combination from day 4 after infection, parasites were cleared from blood and organs within 6 days, but relapses were observed 15 days after the cessation of therapy. When treatment was started at day 1 after infection, 100% of mice survived and relapses were not observed, suggesting a good efficacy of this combination for preventive therapy.

Recent advances in the medical management of early HIV disease

The management of patients who have HIV disease, particularly those in early, asymptomatic disease stages, has recently improved. Clinical trials with zidovudine have demonstrated efficacy and greatly reduced toxicity when the drug is used for asymptomatic HIV-infected persons who have fewer than 500 CD4+ cells/mm3. Also, the optimum dose of zidovudine is lower than previously believed, probably in the range of 300-500 mg daily in oral divided doses. The use of antibiotics to prevent Pneumocystis carinii pneumonia (PCP) is also of clear value for HIV-infected asymptomatic or symptomatic persons with fewer than 200 CD4+ cells/mm3. While aerosolized pentamidine is the only regimen approved for PCP prophylaxis, oral drugs, such as trimethoprim/sulfamethoxazole or dapsone, also appear effective. Together, these and similar advances argue for the widespread use of voluntary HIV testing to enable optimum medical monitoring and appropriate intervention. These issues and recommendations for laboratory and clinical monitoring are provided in this review.

Oral therapy for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. A controlled trial of trimethoprim-sulfamethoxazole versus trimethoprim-dapsone

BACKGROUND

Antimicrobial drugs that can be taken orally are needed for the treatment of Pneumocystis carinii pneumonia in patients with the acquired immunodeficiency syndrome (AIDS). Preliminary data indicate that dapsone with trimethoprim may be an effective alternative to trimethoprim-sulfamethoxazole, which is frequently toxic.

METHODS

In a double-blind trial, 60 patients with AIDS and mild-to-moderately-severe first episodes of P. carinii pneumonia (partial pressure of oxygen in arterial blood, greater than 60 mm Hg while breathing room air) were randomly assigned to 21 days of treatment with either trimethoprim-sulfamethoxazole (20 and 100 mg per kilogram of body weight per day, respectively) or trimethoprim-dapsone (20 mg per kilogram per day and 100 mg per day).

RESULTS

The orally administered treatment failed because of progressive pneumonitis in 3 of the 30 patients assigned to trimethoprim-sulfamethoxazole and in 2 of the 30 assigned to trimethoprim-dapsone (P greater than 0.3). Major toxic effects required a switch to intravenous pentamidine for 17 patients (57 percent) in the trimethoprim-sulfamethoxazole group, as compared with 9 (30 percent) in the trimethoprim-dapsone group (P less than 0.025). With trimethoprim-sulfamethoxazole, there were more instances of severe chemical hepatitis (six, as compared with one in the trimethoprim-dapsone group) and marked neutropenia (five vs. one). Intolerable rash (three in each treatment group) and severe nausea and vomiting (two in each group) occurred with equal frequency with both drug combinations. Methemoglobinemia occurred in most of the patients treated with trimethoprim-dapsone, but it was asymptomatic and the level exceeded 20 percent in only one patient. Mild hyperkalemia (serum potassium level, 5.1 to 6.1 mmol per liter) also occurred in 53 percent of the patients treated with trimethoprim-dapsone.

CONCLUSIONS

In patients with AIDS, oral therapy with trimethoprim-sulfamethoxazole and with trimethoprim-dapsone are equally effective for mild-to-moderate first episodes of P. carinii pneumonia, but with trimethoprim-dapsone there are fewer serious adverse reactions than with trimethoprim-sulfamethoxazole.

Inhibition of Pneumocystis carinii dihydropteroate synthetase by sulfa drugs

A new reversed-phase high-pressure liquid chromatography assay procedure for dihydropteroate synthetase (DHPS) that involves the elution of the enzyme incubation solution with a series of three solvents of decreasing polarity (ammonium phosphate buffer, 10% methanol, and 50% methanol) was designed. By this procedure DHPS was detected in Escherichia coli and Pneumocystis carinii with specific activities of 450 and 14 U/mg, respectively. A comparison of the effects of five sulfa drugs on P. carinii DHPS activity revealed that dapsone is the most potent of these drugs.

Recent advances in the diagnosis, treatment, and prevention of Pneumocystis carinii pneumonia

In summary, recent advances in our ability to diagnose, treat, and prevent recurrences of pneumocystis pneumonia have significantly improved the clinical management of this infection, especially in HIV-1-infected individuals. As current investigations allow our therapeutic armamentarium in this disease to be strengthened even further, it is likely that pneumocystis pneumonia will pose a diminishing threat to those patients currently most susceptible to this infection.