D

DATA SAFETY AND MONITORING BOARD (DSMB):
An independent committee, composed of community representatives and clinical research experts, that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved.

DDC:
See Zalcitibine.

DDI:
See Didanosine.

DELAVIRDINE:
An FDA approved (04/04/97) non-nucleoside reverse transcriptase inhibitor for use in combination with appropriate antiretrovirals when therapy is warranted for treatment of HIV infection. Also called Rescriptor.

DELETION:
Elimination of a gene (i.e., from a chromosome) either in nature or in the laboratory.

DEMENTIA:
Chronic intellectual impairment (i.e., loss of mental capacity) with organic origins that affects a person's ability to function in a social or occupational setting. See AIDS Dementia Complex.

DEMYELINATION:
Destruction, removal, or loss of the myelin sheath of a nerve or nerves.

DENDRITE:
Any of the usual branching protoplasmic processes that conduct impulses toward the body of a nerve cell.

DENDRITIC CELLS:
Patrolling immune system cells that may begin the HIV disease process by carrying the virus from the site of the infection to the lymph nodes, where other immune cells become infected. Dendritic cells travel through the body and bind to foreign invaders -- such as HIV -- especially in external tissues, such as the skin and the membranes of the gut, lungs, and reproductive tract. They then ferry the foreign substance to the lymph nodes to stimulate T cells and initiate an immune response. In laboratory experiments, the dendritic cells that carry HIV also bind to CD4+ T cells, thereby allowing HIV to infect the CD4+ T cells. CD4+ T cells are the primary immune system cells targeted by HIV and depleted during HIV infection.

DEOXYRIBONUCLEIC ACID (DNA):
The molecular chain found in genes within the nucleus of each cell, which carries the genetic information that enables cells to reproduce. DNA is the principal constituent of chromosomes, the structures that transmit hereditary characteristics.

DEPARTMENT OF HEALTH AND HUMAN SERVICES (DHHS):
The U.S. government's principal agency for protecting the health of all Americans and providing essential human services, especially for those who are least able to help themselves. DHHS includes more than 300 programs, covering a wide spectrum of activities. The Department's programs are administered by 11 operating divisions such as the Centers for Disease Control and Prevention, the Food and Drug Administration and the National Institutes of Health (see the entries for these agencies). DHHS works closely with state and local governments, and many DHHS-funded services are provided at the local level by state or county agencies, or through private-sector grantees. Internet address: http://www.hhs.gov.

DESENSITIZATION:
Gradually increasing the dose of a medicine in order to overcome severe reactions. Desensitization procedures have become popular when administering Bactrim to persons with a history of adverse reactions to the drug. Bactrim is an important drug against PCP infection.

D4T:
See Stavudine.

DHHS:
See U.S. Department of Health and Human Services.

DIABETES MELLITUS:
A metabolic disease in which carbohydrate utilization is reduced and that of lipid and protein utilization is enhanced. Diabetes mellitus occurs when the body produces little or no insulin, or cannot use the insulin that is produced. As a result, unused glucose collects in the blood; this leads to high blood-sugar levels. Insulin is the hormone that allows glucose to leave the bloodstream and enter body cells, where it is used for energy generation or stored for future use. Diabetes mellitus can also lead to long-term complications that include the development of neuropathy (swelling and wasting of the nerves), retinopathy (non-swelling eye disorder), nephropathy (swelling or breakdown disorder of the kidneys) generalized degenerative changes in large and small blood vessels, and increased susceptibility to infections. As related to HIV: In June 1997, the FDA sent a Public Health Advisory letter to health care professionals to report that cases of new onset diabetes mellitus, hyperglycemia or worsening of existing diabetes mellitus were occurring in HIV-infected patients receiving protease inhibitors.

DIAGNOSIS:
The determination of the presence of a specific disease or infection, usually accomplished by evaluating clinical symptoms and laboratory tests.

DIARRHEA:
Uncontrolled, loose, and frequent bowel movements. In the U.S., almost all persons living with AIDS develop diarrhea at some time in the course of their disease. Severe or prolonged diarrhea can lead to weight loss and malnutrition. The excessive loss of fluid that may occur with AIDS-related diarrhea can be life threatening. There are many possible causes of diarrhea in persons who have AIDS. The most common infectious organisms causing AIDS-related diarrhea include cytomegalovirus (see CMV); the parasites Cryptosporidium, Microsporidia, and Giardia lamblia; and the bacteria Mycobacterium avium and Mycobacterium intracellulare. Other bacteria and parasites that cause diarrheal symptoms in otherwise healthy people may cause more severe, prolonged, or recurrent diarrhea in persons with HIV or AIDS. See Giardiasis; Microsporidiosis; Mycobacterium avium complex (MAC).

DIDANOSINE:
A nucleoside reverse transcriptase inhibitor first approved by the FDA in 1991 and used for the treatment of HIV infection when antiretroviral therapy is warranted. Also called ddl, Videx.

DIDEOXYCYTIDINE:
See Zalcitabine.

DIPLOPIA:
Double vision.

DISSEMINATED:
Spread (of a disease) throughout the body.

DNA:
See Deoxyribonucleic Acid.

DOMAIN:
A region of a gene or gene product. See Gene.

DORMANCY:
See Latency.

DOSE-RANGING STUDY:
A clinical trial in which two or more doses of an agent (such as a drug) are tested against each other to determine which dose works best and is least harmful.

DOSE-RESPONSE RELATIONSHIP:
The relationship between the dose of some agent (such as a drug), or the extent of exposure, and a physiological response. A dose-response effect means that as the dose increases, so does the effect.

DOUBLE-BLIND STUDY:
A clinical trial design in which neither the participating individuals nor the study staff know which patients are receiving the experimental drug and which are receiving a placebo or another therapy. Double-blind trials are thought to produce objective results, since the expectations of the doctor and the patient about the experimental drug do not affect the outcome. See Blinded Study.

DRUG-DRUG INTERACTION:
A modification of the effect of a drug when administered with another drug. The effect may be an increase or a decrease in the action of either substance, or it may be an adverse effect that is not normally associated with either drug.

DRUG RESISTANCE:
The ability of some disease-causing microorganisms, such as bacteria, viruses, and mycoplasma, to adapt themselves, to grow, and to multiply even in the presence of drugs that usually kill them. See Cross-Resistance.

DSMB:
See Data Safety and Monitoring Board.

DYSPLASIA:
Any abnormal development of tissues or organs. In pathology, alteration in size, shape, and organization of adult cells.

DYSPNEA:
Difficult or labored breathing.