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Pneumocystis pneumonia (PCP or pneumocystis) is the most common opportunistic infection in people with HIV. Without treatment, over 85% of people with HIV would eventually develop PCP. It has been the major killer of people with HIV. However, PCP is now almost entirely preventable and treatable.

PCP is caused by a fungus. It used to be called pneumocystis carinii, but scientists now call it pneumocystis jiroveci. A healthy immune system can control the fungus. However, PCP causes illness in children and in adults with a weakened immune system.

Pneumocystis almost always affects the lungs, causing a form of pneumonia. People with CD4 cell counts under 200 have the highest risk of developing PCP. People with counts under 300 who have already had another opportunistic infection are also at risk. Most people who get PCP become much weaker, lose a lot of weight, and are likely to get PCP again.

The first signs of PCP are difficulty breathing, fever, and a dry cough. Anyone with these symptoms should see a doctor immediately. However, everyone with CD4 counts below 300 should discuss PCP prevention with their doctor, before they experience any symptoms.


For many years, antibiotics were used to prevent PCP in cancer patients with weakened immune systems. It was not until 1985 that a small study showed that these drugs would also prevent PCP in people with AIDS.

The success in preventing and treating PCP is dramatic. Percentages have been cut by about half for PCP as the first AIDS-defining diagnosis, and for PCP as the cause of death of people with AIDS.

Unfortunately, PCP is still common in people who are infected with HIV for a long time before getting treatment. In fact, 30% to 40% of people with HIV develop PCP if they wait to get treatment until their CD4 cell counts are around 50.

A new anti-PCP drug, DB289, is being studied in a Phase II trial. Early clinical trials showed very good results.

The drugs now used to treat PCP include TMP/SMX, dapsone, pentamidine, and atovaquone.

  • TMP/SMX (Bactrim® or Septra®) is the most effective anti-PCP drug. It’s a combination of two antibiotics: trimethoprim (TMP) and sulfamethoxazole (SMX).
  • Dapsone is similar to TMP/SMX. Dapsone seems to be almost as effective as TMP/SMX against PCP.
  • Pentamidine (NebuPent®, Pentam®, Pentacarinat®) is a drug that is usually inhaled in an aerosol form to prevent PCP. Pentamidine is also used intravenously (IV) to treat active PCP.
  • Atovaquone (Mepron®) is a drug used in people with mild or moderate cases of PCP who can not take TMP/SMX or pentamidine.


The best way to prevent PCP is to use strong antiretroviral therapy (ART). People who have less than 200 CD4 cells can prevent PCP by taking the same medications used for PCP treatment

Combination ART can make your CD4 cell count go up. If it goes over 200 and stays there for 3 months, it may be safe to stop taking PCP medications. However, because PCP medications are inexpensive and have mild side effects, some researchers think they should be continued until your CD4 cell count reaches 300. Be sure to talk with your doctor before you stop taking any of your prescribed medications.


Bactrim or Septra (TMP/SMX) is the most effective drug against PCP. It is also inexpensive, costing only about $10 per month. It is taken in pill form, not more than one pill daily. Cutting back from one pill a day to three pills a week reduces the allergy problems of Bactrim and Septra, and seems to work just as well.

However, the “SMX” part is a sulfa drug and almost half of the people who take it have an allergic reaction. This usually is a skin rash, sometimes a fever. Allergic reactions can be overcome using a desensitization procedure. Patients start with a very small amount of the drug and take increasing amounts until they can tolerate the full dose.

Dapsone causes fewer allergic reactions than TMP/SMX. It is also fairly inexpensive – about $30 per month. It also is taken as a pill and, like Bactrim or Septra, not more than one pill daily.

Pentamidine involves a monthly visit to a clinic with a nebulizer, the machine that produces a very fine mist of the drug. The mist is inhaled directly into the lungs. The procedure takes about 30 to 45 minutes. You pay for the drug plus the clinic costs, between $120 and $250 per month. Patients using aerosol pentamidine get PCP more often than people taking the antibiotic pills.


PCP, which was the number one killer of people with HIV, is now almost totally treatable and preventable. Strong antiretroviral drugs (ARVs) can keep your CD4 count from dropping. If your CD4 cell count is below 300, talk to your doctor about taking drugs to prevent PCP. Everyone whose CD4 cell count is below 200 should be taking anti-PCP medication.

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