How to prevent PCP

May 2008     View PDF     En español

What medicines are used to prevent PCP?

The most effective drug used to prevent PCP is the double antibiotic Bactrim/Septra (B/S, TMP/SMX, trimethoprim-sulfamethoxazole). Other drugs include dapsone, Mepron (atovaquone), and NebuPent (aerosolized pentamidine).

When taking these medicines, it’s important to take them as prescribed. Talk to your doctor first if you find it hard to stay on them as prescribed. Also, these drugs may interact with other medicines that you’re taking. Make sure your doctor knows what other drugs you use when you start taking a new medicine. As with all medicines that you take, reading the full prescription insert or talking to your doctor or a pharmacist are good ways to know the possible drug interactions.

Bactrim/Septra (B/S)
B/S is an inexpensive and effective drug that prevents PCP and other types of pneumonia, bacterial infections and toxoplasmosis (toxo). Because Septra is a sulfa drug, about half of the people develop an allergic reaction to it. The main side effect is body rash. Other side effects can include, fever, nausea, vomiting, liver and kidney problems, high blood potassium level, sensitivity to sunlight (photosensitivity), low red blood cells (anemia), low white blood cells (neutropenia), or low platelets (thrombocytopenia).

In rare cases, rashes and other side effects may be the early warning signs of a life-threatening condition called Stevens-Johnson Syndrome (SJS). Symptoms can include severe blisters or splotching of the skin; blisters in the mouth, eyes, nose, and genital area; fever; and swelling of the eyelids. Although SJS is rare, people should alert their doctors at the first sign of these side effects.

Even if you have a mild reaction to B/S, your doctor may still want you to use it. This is because it is such an effective drug for both preventing and treating PCP. For people who can be made to tolerate the therapy, they will have a very potent and important drug to use against their PCP. To do so, you will go through a process called desensitization. This involves taking B/S first at very small doses and then slowly increasing it until the proper dose is reached. Almost 70% of people who try this can use B/S without other major problems. Going through this process with an experienced doctor will help ensure its success.

B/S comes in a tablet and in a liquid form for younger children. The standard dose is a double-strength tablet of Bactrim 800mg/Septra 100mg given once a day. It may also be given three times a week, which causes fewer side effects. However, people who take it daily have lower rates of bacterial pneumonia and toxo and in general live longer.

B/S can interact with many drugs, including dapsone, diruetics, methotrexate, phenytoin, slufonylureas, warfarin and HIV drugs.

Dapsone
Dapsone (with or without pyrimethamine) is another antibiotic pill. It isn’t as effective as B/S, and it must be taken with pyrimethamine in order to prevent toxo. Its side effects include rash, nausea and sometimes hepatitis. Although dapsone may be a reasonable option for people who are allergic to B/S, about half may also be allergic to dapsone. The standard dose is prescribed as a 50mg pill 2x/day or a 100mg pill 1x/day.

Dapsone can interact with many drugs, including clofazimine, dideoxyinosine, folic acid antagonists, probenecid, rifampin, trimethoprim and HIV drugs. Many patients who take dapsone should be screened for a G6P enzyme (glucose-6-phosphate) deficiency.

Mepron (atovaquone)
Mepron is as effective as dapsone in preventing PCP. It has fewer and different side effects than dapsone (mostly stomach problems), but it’s more expensive. Mepron is probably active against toxo but not bacterial pneumonia. The standard dose is prescribed as an oral suspension of 1,500mg per day, taken with a fatty meal to help it get absorbed. Because of cost, it’s usually only considered for people who cannot tolerate B/S and/or dapsone, or for those who are believed to not tolerate these other drugs well.

Mepron can interact with many drugs, including Bactrim/Septra, rifabutin, rifampin and HIV drugs.

NebuPent (aerosolized pentamidine)
NebuPent is the least often used treatment. It involves breathing a fine mist of the drug into the lungs through a machine called a nebulizer on a monthly basis. Although it has not proven to be as effective as B/S, it’s a reasonable option for people who cannot tolerate either B/S or dapsone.

The main advantage of NebuPent is that it causes few side effects and does not have to be used daily. The main side effect, a metallic taste in the mouth, usually disappears soon afterwards. It can also cause dry throat, headache and coughing fits, especially for smokers. The main disadvantage is that people who take NebuPent get PCP more often than those who take antibiotics.

Because NebuPent is concentrated in the lungs, it’s not effective in preventing PCP in other parts of the body. It is also not as effective as B/S in preventing other bacterial pneumonias or toxo. This, coupled with its inferiority in preventing PCP, are the main disadvantages of using it.

Most people taking NebuPent go into a clinic every four weeks for treatment. The standard dose is 300mg. A Respirgard II™ nebulizer should be used for taking the dose because it increases how well the drug is absorbed. Pentamidine can interact with many drugs, including cidofovir, foscarnet, certain heart drugs and HIV drugs.

Can I ever stop therapy?

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