Current Diagnosis & Treatment in Infectious Diseases

Section VI - Histoplasma Capsulatum

79. Pneumocystis carinii

James J. Chamberlain MD

Kristen Ries MD

Essentials of Diagnosis

• Pneumocystis carinii, when examined using molecular techniques, most closely resembles a fungus.
• Stains of either bronchoalveolar-lavage (BAL) or transbronchial-biopsy samples yield a diagnosis in > 90% of patients and should be considered the gold standard in diagnosis.
• BAL with transbronchial biopsy increases diagnostic yield to ~ 100%.
• P cariniihas not yet been cultured in vitro.
• Polymerase chain reaction (PCR) (especially on sputum) increases sensitivity but reduces specificity.
• The prophylactic use of aerosolized pentamidine reduces the sensitivity of sputum and bronchoscopic samples.

General Considerations

1. Epidemiology.In 1983, P cariniipneumonia (PCP) was described as the AIDS-defining illness in ≤60% of the first 1000 patients diagnosed with AIDS in the United States. Subsequently, the advent of prophylactic measures has reduced the incidence of PCP presenting as the initial diagnosis for AIDS to < 50% of cases. In addition, the hospitalization rate is also declining for patients with AIDS who also have PCP. This decline has presumably been caused by successful use of prophylaxis against the organism. An analysis from Ontario, Canada, demonstrated that hospital admissions caused by PCP decreased from 48% to 29% over a 2-year period with the initiation of prophylaxis with aerosolized pentamidine. Another Canadian study tracked PCP cases over the decade from 1981 to 1991 and showed that PCP episodes peaked in 1989 and subsequently began to decline.

Of AIDS patients who do not receive prophylaxis against P carinii, ≤80% will develop at least one episode of PCP and ~ 25% of AIDS patients not receiving prophylaxis will die from PCP. Of patients who have experienced PCP as their AIDS-defining illness, ≤70% will develop recurrent disease in the ensuing 2 years without the use of prophylactic medication, and 50% of these cases will occur in the 9 months after the initial episode.

CD4 lymphocyte levels in immunocompromised patients have become the most useful factor in predicting risk for developing P carinii infections. Retrospective data have demonstrated that PCP rarely occurs in patients with CD4⁺ counts of > 200 cells/mm³ and that > 90% of AIDS patients will have a CD4 count of < 200 cells/mm³ in the 2 months before becoming infected with P carinii. The percentage of lymphocytes that are CD4 also seems an important prognostic factor because > 95% of patients had a CD4⁺ percentage of < 20% in the 2 months before infection.

Although P carinii infection in children is clinically similar to that seen in adults, the numbers of CD4 lymphocytes in pediatric patients differ from those of adults and vary by the age of the patient. The relationship of the CD4 count and the age of a child must be understood to ascertain the degree of immunosuppression. Severe immunosuppression in children < 12 months old is seen with a total CD4 count of < 750 cells/mm³ or a CD4 percentage of < 15%. For HIV-infected children between 1 and 5 years old, a CD4 T-lymphocyte count of < 500 cells/mm³ or a CD4 percentage of < 15% is indicative of immunosuppression and increased risk for PCP.

New information suggests that PCP occurs as a result of transmission from human hosts and not from reactivation of latent infection as once thought. The organism is probably not maintained in the lungs of immunocompetent humans for any significant period, and it has been difficult to detect in normal individuals at autopsy. Further support for the theory of person-to-person spread is that PCP infections seem to peak ~ 4 months after winter viruses. The organism may be spread via aerosolized secretions by persons in the community with viral infections. Clustered outbreaks of PCP also suggest person-to-person spread.

Mortality in cases of mild to moderate PCP (partial arterial oxygen pressure [PaO₂] ≥70 mm Hg and alveolar-arterial oxygen gradient [A-a] ≤35 mm Hg) has substantially decreased as physicians treating the disease have gained experience. The early to mid 1980s saw mortality rates of ≤25% in mild to moderate disease. More recent large, multicenter trials have demonstrated mortality rates of < 1%. However, patients with PCP who develop respiratory failure still suffer profound mortality rates (≤45–72%).

1. Microbiology.P cariniiis an obligate extracellular organism that characteristically evolves from a trophozoite of a single cell into a 5 to 10-mm-diameter cyst that contains up to eight sporozoites, each 1 to 2 mm in size. The developed cysts release sporozoites, which evolve into trophozoites. The majority of organisms in pulmonary tissue exist in the trophozoite form.

The molecular biology of P carinii is interesting, and new discoveries have led to significant modification in the understanding and classification of this organism. P carinii has long been considered a member of the protozoan kingdom. However, in 1988, P carinii ribosomal RNA sequences were found to more closely parallel certain fungal ribosomal RNA sequences. More recent inspection of P carinii gene sequences and fungal sequences from each of the seven fungal phyla seems to suggest that P carinii is a fungal organism. In particular, there appears a noticeable morphologic similarity between P cariniiand the ustomycetous red yeast fungi, which is evidenced by a striking resemblance in mitochondrial RNA segments by PCR analysis.

It is interesting that the strain of P carinii that infects organisms may not be clonal. Within humans, the organism appears to be genetically diverse; isolates from four distinctly different geographic regions of the world show DNA diversity. Different mammalian hosts appear to harbor genetically diverse strains of P carinii as well. P carinii has been proven unable to grow when organisms from one species are deposited in the lungs of a differing species.

1. Pathogenesis.Recent data continue to suggest that P cariniiinfections are acquired via inhalation between hosts. Thus, infectious episodes are thought to occur as a result of reinfection and are not caused by reactivation of latent organisms. Once acquired, the organisms seem to adhere to alveolar cells of the lung. Replication of the organism is slow, and the resultant host immune response is relatively deliberate as well.

Impaired gas exchange at the alveolar level, a hallmark of PCP infection, appears to be caused by both the extensive proliferation of P carinii organisms and the subsequent host response. The presence of a foamy alveolar exudate, alveolar macrophages, interstitial edema, and type I alveolar cell destruction has been demonstrated by electron and light microscopy during the course of infection. The efficacy of corticosteroids in moderate to severe PCP infection is presumably caused by blunting of the host immune response. The importance of the correlation between the degree of immune response and the severity of disease is supported by the association between the number of neutrophils seen on BAL specimens and increased mortality.

CLINICAL SYNDROMES

P CARINII PNEUMONIA

Clinical Findings

1. Signs and Symptoms.The triad of shortness of breath with exertion, nonproductive cough, and fever describes the typical case of PCP (Box 79-1). Symptoms are usually slow to progress and typically worsen over several weeks to months. Cough may be productive of purulent sputum, especially if the patient is concomitantly infected with a bacterial pathogen. Shortness of breath at rest occurs late in the course of disease and signals moderate to severe hypoxia.

The physical exam is relatively nonspecific in diagnosing PCP because ≤50% of patients may have normal pulmonary examinations. Fine rales may be auscultated in ≤40% of patients, most with severe PCP. Patients may have restriction of their inspiratory ability, which is usually not mentioned unless the patient is questioned specifically.

1. Laboratory Findings.The serum lactate dehydrogenase (LDH) level has long been considered a useful laboratory value in the diagnosis of PCP. However, although LDH sensitivity may be > 80%, the test lacks specificity. The serum LDH level does appear to be of prognostic value. Serum LDH levels have been shown to portend a poor prognosis and increased mortality if they are elevated at diagnosis or if they persistently rise despite treatment.
2. Imaging.The chest radiograph is an important tool in the assessment of patients thought to be infected with PCP. Although nearly any pattern may be seen on chest radiograph, the typical appearance seen in ~ 80% of cases is one of diffuse bilateral interstitial infiltrates. Chest radiographs that show consolidation, nodularity, or cavitations may be seen in < 5% of cases. The finding of pneumothoraces, cysts, or pneumatoceles is not uncommon in patients with advanced disease. Of patients with PCP, ≤10% may have cysts (as seen on chest radiographs) and ≤6% may have pneumothoraces. The vast majority of AIDS patients with a pneumothorax have active P cariniiinfections.

EXTRAPULMONARY P CARINII INFECTIONS

Extrapulmonary P carinii infections occur in < 3% of patients and must be diagnosed with histopathologic samples. Primary prophylaxis for PCP with pentamidine may confer a higher risk for extrapulmonary infection. Symptoms of extrapulmonary involvement are nonspecific, usually consisting of fevers, chills, and sweats. Although any area of the body may be involved, splenomegaly with cysts and thyroiditis are most common.

BOX 79-1 Signs and Symptoms of Pneumocystis carinii Pneumonia

More Common Less Common · Fever · Cough (usually nonproductive) · Dyspnea (especially with exertion) · Elevated lactate dehydrogenase · Diffuse interstitial infiltrates on chest radiograph · Pneumothorax (especially if prophylactic treatment with pentamidine) · Pleural effusions rare

Diagnosis

The practice of diagnosing PCP morphologically by traditional staining methods (silver methenamine and toluidine blue) of induced sputum samples in HIV-infected individuals has fallen out of favor. Although relatively simple and inexpensive, staining of sputum samples induced by hypertonic saline inhalation is clearly dependent on operator and laboratory experience, and sensitivity varies tremendously between centers. These classic staining techniques yield a diagnosis in only 30–90% of patients suspected of being infected with PCP. Subsequently, a large number of patients may continue to be treated with potentially toxic drug regimens without a definitive diagnosis. The practice of indirect immunofluorescent stain with monoclonal antibodies has increased the sensitivity of induced sputum samples to ~ 70% or to > 90% in some reports.

Bronchoscopy with BAL with or without transbronchial biopsy has become the gold standard in the diagnosis of PCP. Several studies have demonstrated a sensitivity of > 90% for both BAL and transbronchial biopsy. The combination of BAL and transbronchial biopsy leads to a sensitivity of ~ 100%. The complications of transbronchial biopsy, including bleeding and pneumothorax, have led most clinicians to use BAL as the initial diagnostic method during bronchoscopy if diagnosis is not obtained by induced sputum.

PCR technology on induced sputum samples has improved sensitivity to ~ 100% but appears to result in diminished specificity. PCR may become a reasonable diagnostic tool as PCR technique improves, resulting in less contamination and fewer false-positive results.

Chemoprophylaxis for PCP with aerosolized pentamidine has led to a considerable reduction in the rate of recovery of PCP in sputum and bronchoscopy samples. Performing BAL bilaterally or on multiple lobes seems to maintain sensitivity at > 90%.

Treatment

The primary treatment of moderate to severe pulmonary or extrapulmonary infection caused by P carinii remains the combination of trimethoprim (TMP) and sulfamethoxazole (SMX), either orally or intravenously (IV).

Several medications (atovaquone, trimetrexate, and pentamidine) and combination regimens (dapsone + TMP and clindamycin + primaquine) probably afford nearly equal efficacy to TMP-SMX in mild to moderate PCP and may be better tolerated in specific populations of patients (Boxes 79-2 and 79-3).

1. TMP-SMX.TMP-SMX was the first regimen approved for use in the treatment of PCP, and this regimen is still considered the best initial treatment choice for PCP infection. If tolerated, this combination should be regarded as the initial treatment choice for all PCP infections.

In moderate to severe pulmonary infection with P carinii, TMP-SMX has been shown to significantly improve survival when compared with IV pentamidine (86% vs 61%) in randomized trials. Several drug regimens subsequently discussed appear to have similar efficacy compared with TMP-SMX in mild to moderate PCP and may be better tolerated. However, the fact that TMP-SMX also has excellent antimicrobial activity against organisms causing community-acquired bacterial pneumonia and Toxoplasma infections should be considered when choosing an agent for treating P carinii infections.

Treatment with TMP-SMX is often limited by adverse effects, which occur in the majority of patients to some degree (65–100%). A morbilliform rash is the most commonly observed adverse reaction among patients treated with TMP-SMX; the rash occurs ~ 20–45% of the time and limits treatment in ≤20% of patients. Antihistamines may be used to reduce the severity of the rash. Additional side effects of TMP-SMX include fever, nausea and vomiting, neutropenia, anemia, thrombocytopenia, and elevated serum aminotransferase levels.

1. Pentamidine isethionate.IV pentamidine isethionate is a suitable alternative treatment for PCP if TMP-SMX is not tolerated. Pentamidine appears to be comparable to TMP-SMX in effectiveness in mild to moderate disease. However, a randomized trial comparing IV pentamidine isethionate with TMP-SMX in moderate to severe disease resulted in a significant mortality advantage for patients treated with TMP-SMX (86% vs 61%).

Aerosolized pentamidine isethionate has been used in the treatment of mild to moderate PCP. Unfortunately, although it results in fewer systemic adverse effects, the aerosolized form of pentamidine isethionate has resulted in lower response rates and a higher frequency of relapse. The use of aerosolized pentamidine isethionate is expensive and requires compressed air to be delivered effectively.

The most common adverse effects associated with the use of pentamidine isethionate include nephrotoxicity, hyperkalemia, hypocalcemia, hypomagnesemia, hypoglycemia, and hypotension. The hypotension seems to be related to the rate at which the drug is administered and usually responds to IV fluids. Hyperglycemia and insulin dependence can also occur. Acute pancreatitis has also been reported.

1993. Trimetrexate.Trimetrexate is relatively new in the spectrum of drugs used to treat PCP. The U.S. Food and Drug Administration approved trimetrexate for use in moderate to severe PCP in late 1993. Trimetrexate is related structurally to methotrexate and is thought to possess a similar mechanism of action. Trimetrexate presumably inhibits dihydrofolate reductase, which diminishes the production of nucleic acid precursors, resulting in cell death. Thus, a reduced form of folic acid, folinic acid (leucovorin), must be administered with trimetrexate to reduce toxicity to host cells.

Trimetrexate has been compared with TMP-SMX in a randomized, double-blind, multicenter trial in a group of patients with moderate to severe PCP. Trimetrexate was relatively well tolerated; only 8% of patients terminated treatment before 21 days because of adverse effects. By comparison, 28% of patients who received TMP-SMX had discontinued therapy by 21 days (P < 0.001). However, by 21 days after initiation of treatment, a significantly larger number of patients receiving trimetrexate had been considered treatment failures as measured either by lack of efficacy or death (38%) vs those receiving TMP-SMX (20%). Thus, trimetrexate should be considered a relatively safe treatment option in patients with moderate to severe PCP who do not respond to or are intolerant of TMP-SMX or in patients in whom TMP-SMX is contraindicated.

Trimetrexate, as mentioned, has been well tolerated, with ≤10% of patients discontinuing therapy at 21 days. The principal dose-limiting side effect has been myelosuppression, especially neutropenia and thrombocytopenia, occurring in 10–15% of patients. Elevated serum aminotransferase, alkaline phosphatase, and creatinine levels have been reported as well. Rash and anemia may also occur in patients receiving trimetrexate.

1. Atovaquone.Atovaquone is a hydroxynapthoquinone drug that has proven to be an effective alternative in the treatment of mild to moderate PCP. Several multicenter prospective trials have shown atovaquone to be much better tolerated than either TMP-SMX or pentamidine isethionate. Although atovaquone is somewhat more likely to result in treatment failure, the favorable side effect profile of atovaquone compared with TMP-SMX and pentamidine isethionate has led to equivalent overall clinical success rates of ~ 60–80%. Mortality rates appear similar between atovaquone and pentamidine isethionate ≤8 weeks after completion of treatment. However, mortality appeared significantly higher with atovaquone (7%) as compared with TMP-SMX (0.6%) in a randomized multicenter trial (P= 0.003).

The adverse effects of atovaquone that lead to termination of treatment seem to occur in < 10% of patients over a typical 21-day course of treatment. Gastrointestinal complications arise most frequently and include nausea, vomiting, diarrhea, hepatitis, and constipation. In addition, an erythematous rash has occurred in ≤25% of patients who take atovaquone. Fever and cough are also common side effects.

1. Clindamycin and Primaquine.The use of the combination of clindamycin and primaquine has been proven quite effective in the treatment of mild to moderate PCP.

Several prospective trials have proven that clindamycin and primaquine are ≥90% effective in treating mild to moderate PCP. No significant difference has been demonstrated between clindamycin and primaquine when compared with either TMP-SMX or dapsone-TMP, in mild to moderate disease.

Adverse effects have occurred in up to one-third of patients receiving clindamycin and primaquine, and they may be related to the dose of primaquine used. When primaquine has been dosed at 30 mg/d instead of the more frequently used dose of 15 mg/d, the incidence of dose-limiting side effects has nearly doubled. The most significant dose-limiting adverse effect observed in patients taking clindamycin and primaquine is a vesicular, desquamating, or ulcerating rash. Anemia is a frequent problem as well, which is likely related to the strong oxidative effects of primaquine that lead to its contraindication in patients with glucose-6-phosphate dehydrogenase deficiency. The primaquine component of this treatment combination may lead to methemoglobinemia as well. Less common side effects include nausea and vomiting, neutropenia, and gastrointestinal complaints.

1. Dapsone and TMP.The combination of dapsone and TMP has been shown to possess similar efficacy to TMP-SMX in the treatment of mild to moderate PCP, with significantly fewer treatment-limiting unfavorable effects. Of patients with mild to moderate PCP, > 90% may be expected to respond to treatment with dapsone and TMP.

Adverse reactions to this combination regimen seem to occur at a much lower rate than to either pentamidine or TMP-SMX. Side effects requiring termination of treatment have occurred in < 10% of patients receiving dapsone and TMP. In clinical trials, the major side effects most commonly include rash (occasionally requiring discontinuation of therapy), elevated hepatic transaminases, neutropenia and thrombocytopenia, hemolytic anemia, and methemoglobinemia with serum levels that can exceed 20%. Of note, dapsone is a potent oxidant, an effect that can cause severe hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency, and it should be used with caution in this population of patients.

1. Corticosteroids.The use of corticosteroids has unquestionably been shown to reduce mortality by ~ 50% in patients with moderate to severe PCP. In addition, the need for mechanical ventilation is dramatically reduced in this group of patients. Patients with mild to moderate PCP have not demonstrated benefit from the use of adjuvant corticosteroid use. The suppression of the host inflammatory response to the presence of P cariniiinfection is thought to be the mechanism of the beneficial effect of corticosteroids. Corticosteroid use may exacerbate mucocutaneous herpes simplex, cytomegalovirus infections, and the lesions of Kaposi's sarcoma.

BOX 79-2 Treatment of Pneumocystis carinii Pneumonia in Adults

Treatment Comments First Choice · For mild to moderate infections: Trimethoprim, 15 mg/kg/d, and sulfamethoxazole, 100 mg/kg/d PO or IV, three times daily or four times daily, for 14–21 d (21 d in AIDS) · For moderate to severe infections (see comments): Trimethoprim as above with or without prednisone, 40 mg PO twice, daily for 5 d then 20 mg PO daily for 11 d · Corticosteroids (prednisone) are currently recommended in patients with PO <70 mm Hg or an alveolararterial oxygen gradient (P(A-a)0) > 35 mm Hg. Second Choice · Pentamidine, 3–4 mg/kg IV daily for 14–21 d (21 d in AIDS) · Trimetrexate, 45 mg/m IV daily (over 60–90 min) + folinic acid (leucovorin), 20 mg/m/d PO or IV divided every 6 h for 21 d · Atovaquone suspension, 750 mg PO twice daily for 21 d · Clindamycin, 600 mg IV four times daily or 300–450 mg PO four times daily, + primaquine, 15 mg PO daily for 21 d · Dapsone, 100 mg PO daily + trimethoprim 5 mg/kg PO three times daily for 21 d · Patients with severe disease should probably receive 4 mg of petamidine. · Folinic acid must be administered at the initiation of trimetrexate therapy and continued for 3 d after cessation of therapy. · Atovaquone should be taken with food; failure to do so may result in threefold reduction in absorption. Penicillin Allergic · No change; treat as above

BOX 79-3 Treatment of Pneumocystis carinii Pneumonia in Children

Treatment Comments First Choice · Trimethoprim-sulfamethoxazole, 15–20 mg TMP—75–100 mg SMX/ kg/d IV, PO1divided into four doses, administered one dose per 6 h · Steroids appear to be beneficial in moderate to severe disease · There are no controlled trials of steroids in young children · Suggested dosage 2 mg/kg/d for 7–10 days followed by a tapering dose during the next 10–14 d Second Choice · Pentamidine isethionate, 4 mg base/ kg/d IVfor 10–14 d · Alternatives: trimethoprim and dapsone; primaquine and clindamycin; trimetrexate and folinic acid; atovaquone; for nonsevere disease   1Oral therapy should be reserved for those with mild disease and no evidence of malaborption or diarrhea.

Prognosis

Many clinical markers or scoring systems have been suggested to diagnose and predict outcome in PCP. Most if not all of these factors have been shown to have little value in the management of disease. The degree of hypoxia is an important prognostic factor that affects recommended treatment. The adjuvant use of corticosteroids and choice of treatment regimen should be based on whether the disease is classified as mild to moderate (PaO₂ > 70 mm Hg and P[A-a]O ≤35 mm Hg) or moderate to severe (PaO₂ < 70 mm Hg or P[A-a]O ≥35 mm Hg). However, it is probably better to err on the side of using corticosteroids.

Prevention & Control

Prophylaxis for PCP has clearly been shown to be effective in reducing the incidence of disease and improving survival in patients at risk for developing the disease (Box 79-4). No chemoprophylactic treatment regimen has been shown to be more effective than TMP-SMX. In addition, TMP-SMX provides protection against the bacteria that cause community-acquired pneumonia, as well as against toxoplasmosis. Aerosolized pentamidine isethionate and dapsone with or without pyrimethamine or TMP should continue to be regarded as second-line agents in the prevention of PCP.

• TMP-SMX.No drug regimen has been shown to be more effective for preventing PCP in immunocompromised patients than TMP-SMX. Several primary and secondary prevention trials have proven that TMP-SMX is superior to aerosolized pentamidine isethionate and dapsone in patients who tolerate the drug. Patients who have experienced an initial episode of PCP have a more than threefold greater risk of developing a subsequent recurrence at 18 months while receiving aerosolized pentamidine isethionate than while receiving TMP-SMX. The use of TMP-SMX three times weekly seems to afford protection against P carinii infection that is equal to that from daily treatment.

Of patients receiving prophylaxis against PCP with TMP-SMX, ≤75% may not tolerate the drug. Because TMP-SMX is cheaper and more effective than other treatment options, desensitization protocols have been used to allow some patients who were previously intolerant to TMP-SMX to continue taking the drug. Several published reports indicate that the majority of patients with previous mild to moderate adverse reactions and some with severe anaphylactic responses to TMP-SMX may be safely and successfully desensitized with oral protocols. Thus, most patients who were previously thought to be unable to tolerate TMP-SMX for prophylaxis against PCP may be safely and effectively desensitized with oral desensitization protocols and continue to take TMP-SMX. Some physicians have recommended that all patients who started treatment with SMX should use a desensitization protocol, thus preventing many allergic reactions.

• Dapsone.Dapsone with or without pyrimethamine or TMP is as potent as inhaled pentamidine isethionate but less effective than TMP-SMX in the primary prevention of PCP in HIV-infected individuals. Dapsone is also poorly tolerated, with only 25% of patients in one randomized trial who were able to complete the daily treatment regimen. Dapsone does have the advantage over pentamidine isethionate in efficacy against Toxoplasma infections.

Twice weekly dapsone and pyrimethamine appears to be an effective and perhaps better tolerated alternative to daily dosing regimens. Toxicities associated with prophylactic dapsone are the same as those listed in the treatment section.

• Aerosolized Pentamidine Isethionate.Pentamidine isethionate delivered once monthly via an ultrasonic nebulizer is a reasonable but less effective alternative to oral systemic therapy in PCP prophylaxis. Aerosolized pentamidine isethionate is very well tolerated, with < 15% of patients being unable to tolerate treatment. Unfortunately, aerosolized pentamidine isethionate is more likely to result in extrapulmonary P carinii infection because very little inhaled drug is absorbed systemically. Aerosolized pentamidine isethionate has been shown to reduce the sensitivity of diagnostic procedures used in the diagnosis of PCP as well.

When adverse effects are encountered with inhaled pentamidine isethionate, they are mainly limited to a dry cough and bad taste in the mouth. Spontaneous pneumothorax is a potentially dangerous effect of aerosolized pentamidine isethionate. The small amount of systemic absorption may occasionally result in rash, renal impairment, and pancreatitis. Use of an albuterol inhaler before the nebulized pentamidine isethionate is recommended as routine by some to prevent bronchospasm and to promote better penetration of the drug.

BOX 79-4 Prophylaxis for Pneumocystis carinii Pneumonia

Adults Children First Choice ·  TMP-SMX, 1 DS tablet PO daily or PO 3 times per week, usually on Monday, Wednesday, and Friday ·  TMP-SMX, 5 mg TMP–25 mg SMX/kg/d half given every 12 h or as single dose daily for 3 consecutive d/wk or 7 d/wk Second Choice ·  Pentamidine, 300 mg aerosolized via nebulizer once per month ·  Dapsone, 50–100 mg PO daily or 100 mg PO two times per week with or without pyrimethamine, 50 mg PO 2 times per week, with folinic acid, 10 mg PO (to reduce toxicity) with each dose of pyrimethamine ·  Altovaquone, 1500 mg (10 ml) PO daily ·  Pentamidine, 300 mg nebulized monthly or dapsone 2 mg/kg (not to exceed 100 mg) PO daily

REFERENCES

American Academy of Pediatrics, Committee on Infectious Diseases: Pneumocystis. In Peter G: 1997 Red Book: Report of the Committee on Infectious Diseases, 24th ed. American Academy of Pediatrics, 1997.

Bozzette SA, et al: A randomized trial of three antipneumocystis agents in patients with advance human immunodeficiency virus infection. NIAID AIDS Clinical Trials Group. N Engl J Med 1995;332:693.

Chien SM, et al: Changes in hospital admissions patterns in patients with human immunodeficiency virus infection in the era of Pneumocystis carinii prophylaxis. Chest 1992;102:1035.

Dohn MN, et al: Oral atovaquone compared with intravenous pentamidine for Pneumocystis carinii pneumonia in patients with AIDS. Ann Intern Med 1994;121:174.

Fulton B, Wagstaff AJ, McTavish D: Trimetrexate: a review of its pharmacodynamic and pharmacokinetic properties and therapeutic potential in the treatment of Pneumocystis carinii pneumonia. Drugs 1995;49(4):563.

Girard P-M, et al: Dapsone-pyrimethamine compared with aerosolized pentamidine as primary prophylaxis against Pneumocystis carinii pneumonia and toxoplasmosis in HIV infection. N Engl J Med 1993;328:1514.

Hughes W, et al: Comparison of atovaquone (566C80) with trimethoprim-sulfamethoxazole for the treatment of Pneumocystis carinii pneumonia in patients with the acquired immunodeficiency syndrome (AIDS). N Engl J Med 1993;328:1521.

Kennedy CA, Goetz MB: Atypical roentgenographic manifestations of Pneumocystis carinii pneumonia. Arch Intern Med 1992;152:1390.

Kovacs JA, et al: Diagnosis of Pneumocystis carinii pneumonia: improved detection in sputum with use of monoclonal antibodies. N Engl J Med 1988;318:589.

Lipschik GY, et al: Improved diagnosis of Pneumocystis carinii infection by polymerase chain reaction on induced sputum and blood. Lancet 1992;340:203.

Mason GR, et al: Prognostic implications of bronchoalveolar lavage neutrophilia in patients with Pneumocystis carinii pneumonia and AIDS. Am Rev Respir Dis 1989;139:1336.

Masur H, et al: Consensus statement on the use of corticosteroids as adjunctive therapy for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. N Engl J Med 1990;323:1500.

Miller RF, et al: Pneumocystis carinii infection: current treatment and prevention. J Antimicrob Chemother 1996;37(Suppl B):33.

Nelson JD: Pocket Book of Pediatric Antimicrobial Therapy. Williams & Wilkins, 1998.

Safrin S: New developments in the management of Pneumocystis carinii disease. AIDS Clin Rev 1993/1994:95.

Safrin S, et al: Comparison of three regimens for treatment of mild to moderate Pneumocystis carinii pneumonia in patients with AIDS. Ann Intern Med 1996;124:792.

Sattler FR, et al: Trimethoprim-sulfamethoxazole with pentamidine for treatment of Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. Ann Intern Med 1988;109:280.

Sattler FR, et al: Trimetrexate with leucovorin versus trimethoprim-sulfamethoxazole for moderate to severe episodes of Pneumocystis carinii pneumonia in patients with AIDS: a prospective, controlled multicenter investigation of the AIDS Clinical Trials Group Protocol 029/031. J Infect Dis 1994;170:165.

Sistek CJ, Wordell CJ, Hauptman SP: Adjuvant corticosteroid therapy for Pneumocystis carinii pneumonia in AIDS patients. Ann Pharmacother 1992;26:1127.

Stringer JR, Walzer PD: Molecular biology and epidemiology of Pneumocystis carinii infection in AIDS [editorial]. AIDS 1996;10:561.

Toma E, et al: Clindamycin/primaquine versus trimethoprim-sulfamethoxazole as primary therapy for Pneumocystis carinii pneumonia in AIDS: a randomized, double-blind trial. Clin Infect Dis 1993;17:178.

Wakefield AE, et al: Pneumocystis carinii shows DNA homology with the ustomycetous red yeast fungi. Mol Microbiol 1992;6:1903.

Yung RC, et al: Upper and middle lobe bronchoalveolar lavage to diagnose Pneumocystis carinii pneumonia. Am Rev Respir Dis 1993;148:1563.