Clinical Guide > Comorbidities and Complications > Pneumocystis Pneumonia

Pneumocystis Pneumonia

January 2011

Chapter Contents


Pneumocystis jiroveci pneumonia (previously called Pneumocystis carinii pneumonia, and still abbreviated PCP), is caused by an unusual fungus, P. jiroveci. Many humans appear to be infected in childhood, but clinical illness occurs only in people with advanced immunosuppression, either through new infection or reactivation of latent infection. More than 90% of PCP cases occur in patients with CD4 counts of <200 cells/µL. Cases of PCP in otherwise healthy young homosexual men were among the first recognized manifestations of AIDS, in 1981. The organism can affect many organ sites, but pneumonia is by far the most common form of disease. In the United States, the incidence of PCP has declined sharply since the use of prophylaxis and effective antiretroviral therapy (ART) became widespread, but PCP is still many patients' initial presenting opportunistic infection, and it is a significant cause of morbidity and mortality among HIV-infected patients.

S: Subjective

The patient reports fever, shortness of breath, particularly with exertion, nonproductive cough, night sweats, weight loss, or fatigue. Typically, the symptoms worsen over the course of days to weeks. Pleuritic pain and retrosternal pain or burning also may be present. There may be minimal symptoms early in the disease course of PCP.

Ask the patient about fever, fatigue, and weight loss, which may be present for weeks, with gradual worsening of shortness of breath. PCP may present less commonly with acute onset symptoms of fevers, chills, sweats, dyspnea, and cough.

Note: Given the possibility of HIV-associated tuberculosis (TB), patients with cough should be kept in respiratory isolation until TB is ruled out.

O: Objective

Perform a full physical examination, with particular attention to the following:

Patients may appear relatively well, or acutely ill. Tachypnea may be pronounced, and patients may exhibit such a high respiratory rate (e.g., >30 breaths per minute) that they are unable to speak without stopping frequently to breathe. Chest examination may be normal, or reveal only minimal rales, although coughing is common on deep inspiration. Cyanosis may be present around the mouth, in the nail beds, and on mucous membranes. Cough is either unproductive, or productive of a thin layer of clear or whitish mucus.

A: Assessment

A partial differential diagnosis includes the following:

P: Plan

Diagnostic Evaluation


Presumptive treatment often is initiated on the basis of clinical presentation, chest X-ray findings, and ABG results, while definitive diagnostic tests are pending. The standard and alternative treatment regimens are shown in Table 1.

Standard Therapy


Trimethoprim-sulfamethoxazole (TMP-SMX, Bactrim, Septra, cotrimoxazole) is the drug of choice: 15-20 mg/kg of the TMP component plus 75-100 mg/kg of the SMX component, divided into three or four doses daily and administered IV or PO for 21 days (a typical PO dose is two double-strength tablets TID). Adverse effects of TMP-SMX (e.g., rash, fever, leukopenia, anemia, gastrointestinal intolerance, hepatotoxicity, hyperkalemia) are common, mostly mild, and usually "treated through" successfully. Patients who have had previous reactions to sulfa drugs also may be desensitized successfully (see chapter Sulfa Desensitization). TMP-SMX requires dosage adjustment for patients with renal insufficiency.

Adjunctive corticosteroids

Adjunctive corticosteroids should be given if the patient's PO2 is <70 mm Hg (breathing room air) or the A-a gradient is >35 mm Hg. Corticosteroids should be given as early as possible (preferably before or with the first dose of antibiotic therapy) and within 36-72 hours of the start of anti-PCP therapy:

Table 1. Preferred and Alternative PCP Therapy

* Use with caution in G6PD deficiency (most common among patients of African or Mediterranean descent).
Preferred Therapy
TMP-SMXTMP: 15-20 mg/kg plus SMX: 75- 100 mg/kg in three or four divided doses daily, taken PO or IV for 21 daysPatients who have had previous reactions to sulfa drugs may be desensitized successfully. Adjust dosage for patients with renal insufficiency.
Alternative Therapies
Pentamidine4 mg/kg IV once daily for 21 daysSimilar efficacy to TMP-SMX but greater toxicity (nephrotoxicity, pancreatitis, glucose dysregulation, cardiac arrhythmias). Usually reserved for patients with severe disease who require IV therapy.
Dapsone + trimethoprimDapsone* 100 mg PO once daily plus trimethoprim 15 mg/kg PO per day in 3 divided doses for 21 daysAppropriate for mild-to-moderate disease.
Clindamycin + primaquineClindamycin 600-900 mg IV Q6-8H (or 300-450 mg PO Q6-8H) plus primaquine* base 15-30 mg PO once daily for 21 daysAppropriate for mild-to-severe disease.
Atovaquone750 mg PO BID for 21 daysFor mild-to-moderate PCP only; not as potent as TMP-SMX.

Other therapy notes

Treatment failures

The average time to clinical improvement for hospitalized patients is 4-8 days, so premature change in therapy should be avoided. For patients who fail to improve on appropriate therapy, it is important to exclude other diagnoses, rule out fluid overload, and consult an infectious disease specialist. Some patients do not respond to any therapy, and the mortality rate of hospitalized patients is about 15%.

Secondary Prophylaxis

Anti-PCP prophylaxis (chronic maintenance therapy) should be given to all patients who have had an episode of PCP. Prophylaxis should be continued for life, unless immune reconstitution occurs as a result of ART and the CD4 count has been >200 cells/µL for more than 3 months.

In patients with stable CD4 count of >200 cells/µL on effective ART, it is recommended that PCP prophylaxis be discontinued because it offers little clinical benefit but may cause drug toxicity, drug interactions, and selection of drug-resistant pathogens, plus it adds to the cost of care and to the patient's pill burden.

If PCP occurred at a CD4 count of >200 cells/µL, it is recommended to continue prophylaxis for life despite immune reconstitution; however, data to support this approach are limited.

Prophylactic therapy



* Use with caution in G6PD deficiency.

Primary Prophylaxis

Primary prophylaxis against PCP should be given to all HIV-infected patients with CD4 counts of <200 cells/µL or CD4 percentages of <14%, or a history of oral candidiasis; see chapter Opportunistic Infection Prophylaxis.

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