Acquired Immunity- Immunity that develops during a person's lifetime. There are two types of acquired immunity: active immunity and passive immunity. Active immunity developes after exposure to a disease-causing infectious agent or its antigens, such as following infection or vaccination. Passive immunity develops after receiving lymphocytes or antibodies, such as through breast milk or donated blood components.

Acute HIV infection- also known as Primary HIV infection. Early stage of HIV infection that extends approximately 2-4 weeks from initial infection until the body produces a detectable level of HIV antibodies. Because the virus is replicating rapidely, HIV is highly infectious during this stage of the disease.

Adenovirus- A type of virus that uses double-stranded DNA as its genetic material. Adenoviruses commonly cause respiratory and eye infections. People with weakened immune systems, including people with HIV/AIDS, are at a greater risk for serious complications of adenovirus infection.


Adjuvant- substance added to a drug to enhance the effects of the drug. Also refers to a substance added to a vaccine to boost the body's immune response to the vaccine.

Adverse Drug Reaction- Any unintended, undesirable response to a drug taken at normal dose for normal use. Adverse drug reactions are classified by onset, severity and type.

AIDS Dementia Complex- A progressive neurological condition associated with more advanced HIV infection or AIDS. Symptoms include memory loss, slowed movements, and behavioral changes.

AIDS Encephalopathy- Malfunction of the brain as a result of HIV infection. Can occur as part of acute HIV infection or can result from chronic HIV infection.

Alkaline Phosphatase- An enzyme normally present in certain cells within the liver, bone, kidney, intestine, and placenta. When cells are destroyed in those tissues, the enzymes leaks into the blood, and level rise proportion to the severity of the condition. Measurement of this enzyme is one way to evaluate the health of the liver.

Amino Acid- A building block the body uses to make proteins.

Anaphylaxis- Also called anaphylactic shock. A rare but life-threatening, whole body allergic reaction. Symptoms may appear quickly and include difficulty breathing, swelling of the throat or other parts of the body, rapid drop in blood pressure, dizziness, and unconsciousness. Anaphylaxis can be triggered by foods, drugs, insect stings, or exertion, depending on an individual's sensitivity.

Anemia- A lower than normal number of red blood cells. Symptoms may include fatigue, chest pain, or shortness of breath.

Anorexia- Lack or loss of appetite. In people living with HIV/AIDS, anorexia may be due to HIV infection, secondary infections or medications. Anorexia is also commonly used to refer to anorexia nervosa, which is an eating disorder.

Antineoplastic- A natural or man-made substance that can kill or stop the growth or spread of cancer cells.

Antiprotozoal- A natural or man-made substance that can kill or stop the growth of single-celled micro-organisms called protozoa.

Antisense Drug- A man-made segment of DNA or RNA that can lock onto a strand of DNA or RNA from a virus or other micro-organism. This marks the organism's genetic instructions for destruction and prevents the organism from making more copies of itself.

Bactercide- A natural or manmade substance that kills bacteria.

Bacteriostatic- A natural or manmade substance that can prevent bacteria from production but cannot actually kill existing bacteria.

Bacterium- A microscopic organism consisting of one simple cell. Bacteria occur naturally almost everywhere on earth, including in soil, on skin, in human gastrointestinal tract, and in many foods. Some bacteria can cause disease in humans.

Baseline- An initial measurement (for example, CD4 count or viral load) made before starting treatment or therapy for a disease or condition. In people infected with HIV, the baseline measurement is used as a reference point to monitor HIV infection.

Bilirubin- A yellowish substance excreted by the liver. Its measurement can be used as an indication of the health of the liver. Large quantities of bilirubin may cause the skin to take on a yellow tint (jaundice) and very high levels may cause brain damage.

Bioavailabilty- Rate and extent to which a drug is absorbed and available in the tissues of the body.


Black Box Warning- Information found at the beginning of a drug's prescribing information, manufacturer labeling and promotional material. The information highlights important safety information, such as serious side effects, drug interactions, or use restrictions. The black box warning is one of the strongest warnings issued by the Food and Drug Administration (FDA) and is reserved for drugs with significant risks or monitoring requirements.

Blip- A temporary increase in viral load in someone who previously had undetectable virus and who later returns to having undetectable virus. The viral load during a blip is usually low (50 to 500 copies/mL.).

Booster- An additional dose or doses of a vaccine given after the initial dose to enhance the immune response to the vaccine. Also used as a term to describe a medicine given to enhance another medicine, such as ritonavir (RTV) as a booster with other PIs.

Centers for Disease Control and Prevention (CDC)- A Public Health Service agency responsible (among others) for assessing the status and characteristics of the AIDS epidemic and the prevalence of HIV infections. CDC supports the design, implementation and evaluation of prevention activities, and maintains various HIV/AIDS information services, such as the CDC National AIDS Clearinghouse. An agency of the U.S. Department of Health and Human Services (HHS) that is charged with protecting the health and safety of citizens at home and abroad. The CDC serves as the national focus for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States.

Cell-Mediated Immunity- Immune protection provided by the direct action of immune cells. With this type of immune protection, the response to infectious micro-organisms is performed by specific cells- such as the CD8 cells, macrophages, and other white blood cell-rather than by antibodies. The main role of cell-medicated immunity is to fight viral infections.

Coinfection- Infection with more than one virus, bacterium, or other micro-organism at a given time. For example, an HIV-infected individual may be coinfected with hepatitis C virus (HCV) or tuberculosis (TB).

Combination Therapy- Two or more drugs used together to achieve optimal results in controlling HIV infection. Combination therapy has proven more effective in decreasing viral load than monotherapy (single-drug therapy), which is no longer recommended for the treatment of HIV. An example of combination therapy is the use of two NRTIs plus a PI or an NNRTI.

Complete Blood Count- A general blood test that measures the levels of white and red blood cells, platelets, hematocrit, and hemoglobin in a sample of blood. Changes in the amounts of each of these may indicate infection, anemia, or other health problems.

Concentration- The relative amount of a substance, such as an administered drug or a circulating enzyme, found in a particular location, such as the blood or a specific organ. For example, drug concentrations are often reported as the amount of drug in a measured sample of blood.

Contagious- Easily passable between people through normal day-to-day contact. For example, chicken pox is both an infectious (causing infection) and a contagious disease. In contrast, HIV is an example of an infectious disease that is not contagious disease (i.e., it cannot be passed from person to person through casual contact.

Contraindication- A specific situation in which a particular treatment should NOT be used, because it may be harmful to the patient. For example, some anti-HIV drugs are primarily broken down by the liver and should not be given to people who have liver damage.


Coreceptor- A protein on the surface of a cell that serves as a second binding site for a virus or other molecule. Although the CD4 protein is HIV's primary receptor, the virus must also bind to either the CCR5 or CXCR4 coreceptor to get into a host cell.

Creatinine- A protein found in muscles and blood and excreted by the kidneys into the urine. The level of creatinine in the blood or urine provides a measure of kidney function. Increased levels of creatinine indicate abnormal or impaired kidney function.

Cross Resistance- Cross resistance occurs when a micro-organism has changed, or mutated, in such a was that loses its susceptibility to multiple drugs simultaneously. For examples, HIV resistance to one NNRTI drug usually produces resistance to the entire NNRTI drug class.

Cross Sensitivity- A drug reaction that may occur again with the use of a different, but related. Cross sensitivity can occur with a drug class, such as when a person reacts to all NNRTIs similarly after treatment with just one. Cross sensitivity can also occur among chemically similar drug classes. For example, a person who has a negative side effect to a sulfa-based antibiotic is at risk for the same negative side effect if he or she takes any other sulfa-based drug.

Chancroid- A sexually transmitted disease (STD) caused by a bacterium called Hemophilus ducreyi. Often causes swollen lymph nodes and painful sores on the male sex organ, female sex organ or anus. The lesions appear after an incubation period of 3 to 5 days and may facilitate HIV transmission.

Chlamydia- A sexually transmitted disease (STD) caused by a bacterium called Chlamydia trachomatis. The bacteria infect the genital tract and, if left untreated, can cause damage to the female and male reproductive systems, resulting in infertility.