TreatmentUpdate60; Volume 7, No. 6 - June 1995
Sean Hosein

Although a number of drugs are available to treat and prevent the life-threatening pneumonia PCP, some HIV-infected patients still develop PCP. Researchers in the USA are beginning to investigate these cases of PCP despite use of preventative antibiotics (called PCP prophylaxis).

* STUDY DETAILS

Researchers used data from 473 men who had less than 200 CD4+ cells "within 6 months before they began [taking preventative doses of antibiotics] and 3 other men who had [less than 200 CD4+ cells] within 12 months before they began to use PCP prophylaxis." Thus researchers used data on a total of 476 men. Seventy-seven percent of subjects had never had an attack of PCP before entering this study; their use of preventative antibiotics is called primary prophylaxis. The remaining 23% of subjects had an episode of PCP before entering this study; their use of PCP prevention is called secondary prophylaxis. Drugs used to prevent PCP were Bactrim(R)/Septras (B/S), dapsone and/or aerosol pentamidine (A/P).

* RESULTS-SWITCHING DRUGS

The study began in 1989 with about 20% of subjects using B/S,73% using AP and 7% dapsone. According to the study doctors, "use of [B/S] doubled" during the study. This change happened to the same extent in subjects who had had or who had never had PCP before entering this study.

* RESULTS-PCP

Eventually 19% of subjects developed PCP. Doctors diagnosed PCP in one of two ways:

- analyzing samples from the lungs 73% - improvement in subjects treated with anti-PCP drugs 27%

Half of the subjects who had never had PCP before entering this study developed PCP within 12 months into this study. This group survived for about 2 years.

Half of subjects who had had an episode of PCP before entering this study developed PCP roughly 8 months after entering this study. This group survived for about 1.2 years. This difference in survival between the 2 groups was statistically significant; that is, not likely due to chance alone. Changing the drug used for prevention did not appear to cause PCP. The type of PCP prophylaxis did not affect survival.

Whichever drug subjects used when they first entered the study did not affect survival (in a statistically significant manner). Subjects having relatively high CD4+ cell counts (defined by researchers as 100 or more CD4+ cells) were more likely to stop using anti-PCP drugs than those with lower CD4+ cell counts. This event was statistically significant.

* A DETAILED REVIEW

Reviewing their data and making adjustments for changes over time, researchers found "that the most important independent factor for developing PCP [despite use of preventative drugs] was [a very low CD4+ cell count]."

As well, the following factors appeared to provide protection from PCP:

- use of B/S - cigarette smoking

In their more sophisticated analysis, AZT was not linked to preventing PCP because, after "[CD4+] cell counts were considered, non-users [of AZT] had higher CD4+ cell counts than previous users who had lower cell counts." That cigarette smoking affected which subjects developed PCP is interesting. In earlier studies subjects who smoked cigarettes were more likely to develop PCP than those who didn't. The researchers warn that their results should not be used to encourage patients with HIV/AIDS to smoke as that causes lung problems. According to the researchers, the following proportion of subjects developed PCP at the cell counts listed:

- 85%: who had less than 75 CD4+ cells - 75%: who had less than 50 CD4+ cells

The study doctors decided that the microbe that causes PCP did not become resistant to any of the drugs used by subjects as prophylaxis. Indeed, subjects who used B/S as prophylaxis recovered from PCP when treated with the same drug. Finally the doctors stated that "more effective [regimens against the microbe that causes PCP need to be developed]."

REFERENCES

1. Saah AJ, Hoover DR, Peng Y, et al. Predictors for failure of pneumocystis carinii pneumonia prophylaxis. Journal of the American Medical Association 1995;273(15):1197-1202.

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Copyright © 1995 - TreatmentUpdate. Reproduced with permission. Reproduction of this article (other than one copy for personal reference) must be cleared through the Editor, The Canadian AIDS Treatment Information Exchange, 555 Richmond St. West, Suite 505, Box 1104, Toronto, ON, M5V 3B1 • Phone: 416-203-7122 • Toll Free: 1-800-263-1638 • Fax: 416-203-8284  http://www.catie.ca