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Pneumocystis pneumonia is a serious disease caused by a fungal pathogen called Pneumocystis jiroveci. Although it is typically seen as an opportunistic infection linked to HIV and AIDS, it is also found in patients with hematologic malignancies, as well as in those receiving transplants and immunosuppressive therapy. It can even arise in patients without those risk factors.
Adequate assessment of the severity of pneumonia (by means of medical history, examination findings, chest radiograph and the results of arterial blood gas estimations) should guide decisions about the choice of therapy, which inevitably includes specific antimicrobial drugs.
The first-choice treatment for Pneumocystis pneumonia of all grades of severity is high-dose trimethoprim–sulfamethoxazole given in two to four divided doses. Treatment duration may vary from 7 to 14 days. However, HIV-infected patients should receive this drug for at least 21 days, since shorter courses are often associated with treatment failures.
Unfortunately, adverse effects are often observed. These usually include neutropenia and anemia in up to 40% of patients, followed by rash and fever in 25% and 20% of patients, respectively. Moreover, patients with known allergies to sulfa drugs should never be given this treatment.
Corticosteroids show beneficial effects in HIV-infected patients who have Pneumocystispneumonia with signs of hypoxemia. This refers to a partial pressure of blood arterial oxygen lower than 70 mm Hg measured while the affected individual is breathing room air. Several regimens are in use, the most common being oral prednisolone, and the treatment should be introduced at the start of specific anti-Pneumocystis therapy.
Patients who have mild Pneumocystis pneumonia are usually treated with an oral trimethoprim–sulfamethoxazole regimen as out-patients under the close supervision of a physician. Conversely, all patients with moderate or severe Pneumocystis pneumonia should be treated in hospital with intravenous antimicrobials and adjunctive corticosteroids.
If hypoxemia is present, supplemental oxygen therapy via a tight-fitting face mask should be introduced in order to maintain the adequate partial pressure of arterial oxygen. Sometimes there is even a need for non-invasive ventilatory support by using continuous positive airway pressure (CPAP) ventilation – either by face or nasal mask.
Due to progressive immunosuppression and a low number of CD4+ T lymphocytes, HIV-infected individuals are at increased risk of developing Pneumocystis pneumonia. In order to prevent a first episode of Pneumocystis pneumonia, primary prophylaxis is given when the CD4+ T lymphocyte count drops below 200 cells per µL of blood, as well as to patients with AIDS-defining diagnoses such as Kaposi sarcoma.
On the other hand, secondary prophylaxis is given to prevent recurrence. Prophylaxis in general can also be given to those with high attack rates for Pneumocystis pneumonia. This includes children with severe combined immunodeficiency syndrome, acute lymphoblastic leukemia, rhabdomyosarcoma or Wegener granulomatosis.
In all these cases, oral trimethoprim–sulfamethoxazole is a first-choice regimen for prophylaxis. Alternatively, other less effective agents may be used for this purpose, such as nebulized pentamidine, dapsone, atovaquone or azithromycin. Primary or secondary prophylaxis may be discontinued in HIV-infected individuals who show a good response to highly active antiretroviral therapy (HAART).