Antiretroviral drugs require 95% adherence

According to investigators from the University of Pittsburgh Medical Center, a computerized medication monitoring system has shown that HIV patients must be at least 95% adherent to antiretroviral therapy for the drugs to work. The study also reveals that physicians often are wrong about their patients' adherence. Results of the study were published in the Annals of Internal Medicine (vol. 133, no. 1).

"For HIV therapy to be effective, patients cannot afford to skip or delay any pills in their daily regimen, and it is vital that doctors know exactly how adherent each patient is," said David L. Paterson, chief of infectious diseases at UPMC's new hospital in Palermo, Italy, and principal investigator on the study. "However, this study shows that, in almost half the cases, physicians are mistaken about their patients' adherence. Those mistakes could have serious consequences."

Physicians in the study miscategorized adherence for 41% of their patients. Researchers were especially concerned about physicians' underestimation of a patient's adherence, as this belief may make a physician reluctant to prescribe a complex "drug cocktail." Conversely, overestimation of adherence may lead a physician to change therapies based on a mistaken belief that the drugs are ineffective. In reality, the patient simply may be skipping doses.

The study involved 81 patients at HIV clinics at the Veterans Affairs Medical Center in Pittsburgh and the University of Nebraska Medical Center in Omaha, who were taking protease inhibitors.

Researchers followed patients' drug adherence with the computerized Medication Events Monitoring System. Microprocessors in medication bottle caps recorded each opening and showed the date, time and duration of opening. Scanning the cap over a communicator module recorded medication dosing. Percentage of adherence was calculated by dividing the number of prescribed doses by the number of doses taken.

Investigators found that patients with 95% or greater adherence had a greater chance of success, as measured by disappearance of detectable HIV in their bloodstream, greater increases in CD4 lymphocyte count and lower hospitalization rates than did patients with levels of adherence lower than 95%.

Said Nina Singh, M.D., co-principal investigator on the study, "Doctors realize that the drug regimens are difficult, but without a high degree of adherence, the medications will be ineffective."

Investigators also found that only 28% of patients studied were able to reach the required 95% level of adherence. Those patients with low adherence were more likely to have problems with alcoholism and depression than were those with at least a 95% adherence level.

"Clearly, we must increase our efforts to diagnose and treat active depression in patients infected with HIV as a potential strategy to improve adherence," said Paterson. "Numerous studies on medication adherence have associated the presence of psychiatric illness with decreased adherence to therapy, and in this case it can be a matter of life and death." PR