Acidophilus: Bacteria that when ingested, help restore the normal bacterial populations in the digestive tract. Found in live yoghurt cultures, it may be useful in preventing thrush.

ACTG: AIDS Clinical Trial Group is the US Government group that co-ordinates drug trials.

Active Immunity: Resistance resulting from previous exposure to an infectious agent or antigen may be active and specific, as a result of naturally acquired infection or intentional vaccination (artificial active immunity), or it may be passive immunity.

Acupuncture: A Chinese medical treatment involving the insertion of very fine sterile needles into the body at specific points according to a mapping of "energy pathways." Historically, acupuncture is one component of an overall program of Chinese medicine that includes theory, practice, diagnosis, physiology, and the use of herbal preparations. Acupuncture is used to control pain and to treat other conditions such as allergies or addiction withdrawal.

Acute: Describing a disease of rapid onset, severe symptoms and brief duration.

Acute HIV Infection: The 4-to-7-week period of rapid viral replication immediately following exposure. The number of virions produced during primary infection is similar to that produced during several subsequent years of established, asymptomatic infection. An estimated 30 to 60 percent of individuals with primary HIV infection develop an acute syndrome characterised by fever, malaise, lymphadenopathy, pharyngitis, headache, myalgia, and sometimes rash. Following primary infection, seroconversion and a broad HIV-1 specific immune response occur, usually within 30 to 50 days. It was previously thought that HIV was relatively dormant during this phase. However, it is now known that during the time of primary infection, high levels of plasma HIV RNA can be documented.

Acyclovir (Zovirax®): An antiviral drug used in the treatment of herpes simplex and herpes zoster.

Adherence: The extent to which a patient takes his/her medications according to the prescribed schedule (also called "compliance"). Nonadherence may jeopardise the effectiveness of a drug and lead to drug resistance.

Adjuvant: A substance in a vaccine to make it more effective or a drug used to help another to combat an illness.

Administration: How a drug is introduced into the body e.g. by mouth or injection.

Adverse Event: An unwanted side effect of a drug, toxicity (see "Side Effect").

Aetiology: The study or theory of factors that cause disease.

Agenerase®: See "Amprenavir."

AIDS (Acquired Immunodeficiency Syndrome): A state of severe immune suppression brought about by infection with HIV. A diagnosis of AIDS is given to a person with HIV infection who experiences an AIDS-defining illness; the condition may be an opportunistic infection like CMV or cancers like lymphoma.

AIDS Cognitive and Motor Deficit Complex: Previously referred to as AIDS dementia Complex or, simply, dementia. This condition is wide-ranging, encompassing symptoms from early as well as late state infection. Symptoms include memory loss, poor concentration, visual disturbances, motor impairment and personality changes.

AIDS-Related Complex: see "ARC."

Alkaline Phosphatase: An enzyme normally present in certain cells within the liver, bone, kidney, intestine, and placenta. When the cells are destroyed in those tissues, more of the enzyme leaks into the blood, and levels rise in proportion to the severity of the condition. Measurement of this enzyme is used as an indication of the health of the liver.

Allopathic: A term to describe conventional medicine by alternative and complementary practitioners.

Alpha Interferon: A natural protein produced by the body in response to infection and produced by pharmaceutical companies as Intron A, Roferon-A and Wellferon. Used in the treatment of KS and hepatitis C.

ALT (Alanine aminotransaminase): A liver enzyme that plays a role in protein metabolism. Elevated levels of ALT are a sign of liver damage from disease or drugs.

Alternative Medicine: This phrase describes medical approaches that differ from Western, drug-based medicine. It includes Chinese medicine, acupuncture, and homeopathy, among other treatments.

Amino Acid: Any one of 20 or more organic acids that are the building blocks of protein, necessary for metabolism and growth.

Amoebiasis: Infection with amoebas, a type of protozoan, especially Entamoeba histolytica. Amoebas invade the bowel mucosa causing ulceration and bloody diarrhoea. Transmission is by contaminated water or oral-faecal transfer.

Amdoxovir: see "DAPD."

Amphoteracin B (Fungizone, Abelcet): Polyene antibiotic used to treat cryptococcal meningitis. Given intravenously. Also used for severe fungal infections that have not responded to conventional treatment. Strong side effects.

Amprenavir (Agenerase®): A protease inhibitor that must be taken twice a day with or without food. Side effects include rash, fatigue and vomiting.

Anabolic Steroid: A synthetic steroid used to increase muscle mass and weight.

Anaemia: A condition in which the blood is not able to deliver enough oxygen to the tissues. Too few red blood cells, impaired red blood cells, or insufficient/ineffective haemoglobin may cause anaemia. Symptoms of anaemia include tiredness, shortness of breath and headache.

Analgesic: Refers to a compound (drug e.g. aspirin) or treatment that reduces pain.

Anaphylaxis: A severe allergic reaction, usually to a drug. Symptoms include breathing difficulties, low blood pressure and rash, sometimes with blisters or hives. This requires immediate medical attention as this condition is potentially life threatening.

Angiogenesis: The process of forming new blood vessels. Angiogenesis is essential for the growth of tumours, especially Kaposi's Sarcoma.

Anogenital: Refers to area that includes the genitals, perineum and anus.

Antibiotic: A drug that slows bacterial growth or kills bacteria.

Antibody: A natural substance made by B cells (which are a type of white blood cell) that is specifically designed to neutralise an invading organism. HIV has a much smaller effect on the body's ability to produce antibodies compared to its other effects on the immune system.

Antidepressant: An agent that elevates the mood and prevents or alleviates psychological depression. Antidepressant drugs are sometimes used as adjuvant analgesic to relieve neuropathic pain. Heterocyclic and tricyclic classifications refer to antidepressants with specific chemical structures. Other classes of antidepressants include MAO inhibitors and serotonin reuptake inhibitors (e.g., Prozac).

Antiemetic: An agent that prevents vomiting.

Antifolate: An agent that inhibits intracellular (e.g., inside cells) production of folinic acid.

Antifungal: A substance that kills or inhibits the growth of a fungus.

Antigen: A portion of a foreign substance or organism (such a virus like HIV or CMV) against which B cells design an antibody. Antibodies neutralise antigens.

Antihistamine: An agent that counteracts the effects of histamine; antihistamines are used to treat allergic reactions and to block stomach acid production.

Antiretrovirals: A class of drugs that inhibit retroviruses like HIV.

Antisense Drugs: An antisense, nucleic acid-related compound is the mirror image of the genetic sequence that it is supposed to inactivate. It is a synthetic segment of DNA or RNA that locks onto a strand of natural DNA or RNA with a complementary sequence of nucleotides. By binding to either the target DNA or RNA, the antisense drug prohibits the normal functioning and expression of the gene. This prevents the building of new virus particles or the infection of new host cells. The antisense drug fomivirsen is used for the treatment of CMV retinitis, a viral infection that often leads to blindness in patients with AIDS.

Antiviral: A substance or process that destroys a virus or suppresses its replication (i.e., reproduction).

Antiviral-Naïve: Refers to a person who has never taken any anti-HIV drugs before.

Aphthous Ulcer: Very painful sore in the mouth or throat treated with steroids or thalidomide.

Apoptosis: "Cellular suicide," also known as programmed cell death. HIV may induce apoptosis in both infected and uninfected immune system cells. Normally when CD4+ T cells mature in the thymus gland, a small proportion of these cells is unable to distinguish self from nonself. Because these cells would otherwise attack the body's own tissues, they receive a biochemical signal from other cells that results in apoptosis. see "Tumour Necrosis Factor."

ARC (AIDS-Related Complex): This is an old term that is used to describe a collection of symptoms in a person with HIV who does not have a diagnosis of AIDS. The term is rarely used today.

Area Under the Curve (AUC): In pharmacokinetics, the evaluation of the body's exposure over time to a given drug. AUC's are used as a guide for dosing and to compare the different drugs' availability in the body.

Arthralgia: Pain in a joint.

Aspergillosis: A fungal infection caused by Aspergillus. Can cause lung problems in people with HIV, and can sometimes affect other parts of the body.

Assay: A test used to detect the presence or concentration of a drug, virus or other substance in bodily fluids or tissues.

Asymptomatic: Without symptoms, clinically normal.

Atazanavir (Reyataz ®): A protease inhibitor manufactured by Bristol-Myers Squibb. Blue capsules in 150mg and 200 mg doses. Side effects include back pain, diarrhoea and GI discomfort.

Atherosclerosis: "Hardening of the arteries" in which cholesterol and other deposits build up on the inner walls of the artery, limiting the flow of blood.

Atrophy: A wasting or shrinking of cells, tissues, organs or muscle.

Attenuated: Weakened or decreased. For example, an attenuated virus can no longer produce disease but might be used to produce a vaccine.

Atypical: Not usual.

Autoimmunity: A reaction to one’s own tissues to which tolerance has been lost.

Azithromycin: An antibiotic used to treat MAC.

Azole drug: A class of drugs used to fight fungal infections. There are 2 subclasses, the imidazoles (e.g., clotrimazole, ketoconazole) and the triazoles (e.g., fluconazole, itraconazole).

AZT (Retrovir®, zidovudine, ZDV): The first drug licensed to treat HIV. Today it is almost always used in combination with other anti-HIV drugs. Side effects include nausea, vomiting, and low red or white blood cell counts. Also used to prevent transmission of HIV from mother to foetus.