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Bacteremia is the presence of bacteria in the blood.

B-Cell (B-Lymphocyte) type of lymphocyte that is a precursor to plasma cells. During infections, individual B-cell clones multiply and are transformed into plasma cells, which produce large amounts of antibodies against a particular antigen on a foreign microbe. This transformation occurs through interaction with the appropriate CD4 T-helper cells.

Bilayer is a term used to describe the structure of a lipid membrane that forms two separate aqueous phases.

Bioactive conformation is biologically active conformation of the inhibitor, substrate, antagonist, or agonist that binds to the active/binding site. This is usually obtained from an X-ray structure of the substrate or a known inhibitor bound to the active site of an enzyme/receptor or bound to a similar site. It is sometimes inferred from extensive conformational mapping along with information about the active site and mutations in the drug and/or binding site.

Bioassay is a procedure for determining the concentration, purity, and/or biological activity of a substance (e.g., vitamin, hormone, plant growth factor, antibiotic, enzyme) by measuring its effect on an organism, tissue, cell, enzyme or receptor preparation compared to a standard preparation.

Bioisostere is a compound resulting from the exchange of an atom or of a group of atoms with another, broadly similar, atom or group of atoms. The objective of a bioisosteric replacement is to create a new compound with similar biological properties to the parent compound. The bioisosteric replacement may be physicochemically or topologically based. (See also Isostere) Bioprecursor prodrug is a prodrug that does not imply the linkage to a carrier group, but results from a molecular modification of the active principle itself. This modification generates a new compound, able to be transformed metabolically or chemically, the resulting compound being the active principle.

Biopsy is theremoval of a small sample of tissue either surgically or with a small needle for microscopic examination to determine whether the subject has a particular disease.

Biotransformation is the chemical conversion of substances by living organisms or enzyme preparations.

Bone Marrow Suppression is a side effect of many anticancer and antiviral drugs, including AZT Bone marrow suppression leads to a decrease in white blood cells, red blood cells and platelets. Such reductions in turn result in anemia, bacterial infections and spontaneous or excess bleeding.

Bronchitis is a disease marked by inflammation of the bronchial tubes in the lungs.

Bronchoscopy refers to a diagnostic examination in which tubes are inserted in the throat that allow doctors to see the trachea and the lungs. Bronchoscopy is often used to detect PCP.

Cachexia a general weight loss and wasting occurring in the course of a chronic disease.

Candida is a group of yeast-like fungi, in particular Candida albicans that infect the mouth as well as other mucous membranes in the esophagus, intestines, vagina, throat and lungs. Oral or recurrent vaginal candida infection is an early sign of immune system deterioration.

Candidiasis is an infection due to candida yeast. The symptoms of oral candidiasis (thrush) and vaginal candidiasis (formerly called monilia) include pain, itching, redness and white patches in their respective sites. Some common treatments are clotrimazole, nystatin and miconazole.

Carbohydrate derives their name from the general formula of carbohydrate is C_x(H₂O)_y - x and y may or may not be equal and range in value from 3 to 12 or more. For example glucose is: C₆(H₂O)₆ or is more commonly written, C₆H₁₂O₆. The chemistry of carbohydrates most closely resembles that of alcohol, aldehyde, and ketone functional groups. As a result, the modern definition of a CARBOHYDRATE is that the compounds are polyhydroxy aldehydes or ketones. [TABLE OF SACCHARIDES]

Carrier-linked prodrug (Carrier prodrug) is a prodrug that contains a temporary linkage of a given active substance with a transient carrier group that produces improved physicochemical or pharmacokinetic properties and that can be easily removed in vivo, usually by a hydrolytic cleavage.

Cascade prodrug is a prodrug for which the cleavage of the carrier group becomes effective only after unmasking an activating group.

Catabolism reactions involving endogenous organic substrates to provide chemically available energy (e.g., ATP) and/or to generate metabolic intermediates used in subsequent anabolic reactions.

Catabolite a naturally occurring metabolite.

CD8 Cell: one type of T-lymphocyte which bears the CD8 molecular marker on its surface. Some CD8 cells recognize and kill cancerous cells and those infected by intracellular pathogens (some bacteria, viruses and mycoplasma). These cells are called cytotoxic T-lymphocytes (see).

CD4: the protein structure on the surface of a human cell that allows HIV to attach, enter, and thus infect a cell. CD4 receptors are present on CD4 cells (helper T-cells), macrophages and dendritic cells, among others. Normally, CD4 acts as an accessory molecule, forming part of larger structures (such as the T-cell receptor) through which T-cells and other cells signal each other.

CD4 Cell: a type of T-cell involved in protecting against viral, fungal and protozoal infections. The CD4 cell modulates the immune response to an infection through a complex series of interactions with antigen presenting cells (macrophages, dendritic cells and B cells) and other types of lymphocytes (B-cells and CD8 cells). Other names for CD4 cell are T-helper cell or helper T-cell.

CD4 Cell Count: the most commonly used surrogate marker for assessing the state of the immune system. As CD4 cell count declines, the risk of developing opportunistic infections increases. The normal range for CD4 cell counts is 500 to 1500 per cubic millimeter of blood. CD4 count should be rechecked at least every six to twelve months if CD4s are greater than 500/mm3. If the count is lower, testing every three months is advised.

CD4/CD8 Ratio: the ratio of CD4 to CD8 cells. A common measure of immune system status is around two in healthy individuals.

Cerebrosideis a sphingolipid whose polar head is comprised of a neutral saccharide.

Chemotaxis is the phenomenon that results from the biased spatial orientation of the movements of cells in the direction of a chemoattractant concentration gradient.

Chemotherapy: the use of chemical agents (drugs) in the treatment of a disease. The term commonly, but not always, refers to cancer treatment.

Chlamydia: the most common sexually transmitted bacterium (Chlamydia trachomatis), that infects the reproductive system. The infection is frequently asymptomatic, but if left untreated, it can cause sterility in women.

Chronic: refers to symptoms and diseases that last for an extended period of time without noticeable change.

Clearance is at the simplest level the rate of elimination by all routes relative to the concentration of drug in any biological fluid. Typically it is reported as blood clearance, plasma clearance or clearance based on unbound drug concentration.

Clinical Trials commonly referred to as a clinical study or research study, aredesigned to determine if a new drug or treatment will work on a disease or will potentially be of benefit to patients. Typically clinical trials have four stages or phases. Phase I study is the first use of a new drug or a new drug indication in humans. It is used to test for safety and side effects, and to determine how the drug should be given. Only a limited number of patients are accepted for participation in Phase I trials. If the Phase I trial shows safety, a Phase II trial is initiated to investigate the ideal dosing range of the drug. The therapy is tested in a larger number of patients to determine how well it works, and other possible, less common side effects. In a Phase III trial, treatments are compared to common or standard therapies. Patients who participate in Phase III trials are randomized (randomly chosen) to receive the trial drug treatment and/or a standard therapy. Those patients who are selected to receive standard therapy for their indication are referred to as the control group. The purpose of a Phase III trial is to determine if the experimental therapy is more beneficial than or adds any benefit to the standard therapy. A Phase IV clinical trial may be conducted to continue evaluation of the safety and efficacy of therapies that are already FDA approved and available for general use.

Clone is a population of genetically identical cells produced from a common ancestor. Sometimes, .clone. is also used for a number of recombinant DNA (deoxyribonucleic acid) molecules all carrying the same inserted sequence.

Codon is the sequence of three consecutive nucleotides that occurs in mRNA which directs the incorporation of a specific amino acid into a protein or represents the starting or termination signals of protein synthesis.

Coenzyme is a dissociable, low-molecular weight, non-proteinaceous organic compound (often nucleotide) participating in enzymatic reactions as acceptor or donor of chemical groups or electrons.

Cohort is a group of individuals with some characteristics in common that is the subject of a study of the epidemiology or natural course of a disease.

Combinatorial synthesis is a process to prepare large sets of organic compounds by combining sets of building blocks.

Combinatorial library is a set of compounds prepared by combinatorial synthesis.

Computer-assisted drug design (CADD) involves all computer-assisted techniques used to discover, design and optimize biologically active compounds with a putative use as drugs.

Congener is a substance literally con- (with) generated or synthesized by essentially the same synthetic chemical reactions and the same procedures. Analogs are substances that are analogous in some respect to the prototype agent in chemical structure. Clearly congeners may be analogs or vice versa but not necessarily. The term congener, while most often a synonym for homologue, has become somewhat more diffuse in meaning so that the terms congener and analog are frequently used interchangeably in the literature.

Control Arm are the group of participants in a clinical trial who receive standard treatment or a placebo, against which those receiving the experimental treatment are compared.

Controlled Trial is a clinical study in which one group of participants receives an experimental drug while another group receives either a placebo or an approved standard therapy. When participants do not know which group they are in, the trial is blinded. Double-Blind trial.

Cooperativity is the interaction process by which binding of a ligand to one site on a macromolecule (enzyme, receptor, etc.) influences binding at a second site, e.g. between the substrate binding sites of an allosteric enzyme. Cooperative enzymes typically display a sigmoid (S-shaped) plot of the reaction rate against substrate concentration. (See also Allosteric binding sites).

Cross-Resistance is the phenomenon in which a microbe that has acquired resistance to one drug through direct exposure also turns out to have resistance to one or more other drugs to which it has not been exposed. Cross-resistance arises because the mechanism of resistance to several drugs is the same and arises through the identical genetic mutations.

Cytochrome P450 (CYP) is a series of metabolizing enzymes that carry out first pass metabolism of xenobiotics. CYP isoforms include CYP1A1 CYP1A2 CYP1B1 CYP2A6 CYP2A13 CYP2B6 CYP2C8 CYP2C9 CYP2C19 CYP2D6 CYP2E1 CYP2J2 CYP3A4 CYP3A5 CYP4F1 CYP5A1 CYP8A1 CYP21

Cytochrome P450 induction: an increase in the activity of a CYP enzyme after prolonged (hours or days) chemical exposure. Certain transcriptions factors could be monitored. Genes belonging to families CYPs 1-4 are transcritionally activated by foreign chemicals through one of four receptor mediated mechanisms, cytosolic receptor for CYP1 family; and three nueclear orphan receptorsof the nuclear steroid receptor superfamily: CAR (constitutive Androstane Receptor for CYP2; PXR (Pregnane X receptor) or SXR (Steroid xenobiotic receptor) which activates CYP3A and PPAR (Peroxisome proliferator Activated Receptor) which mediates induction of CYP4 family.

Cytokines are proteins produced by white blood cells that act as chemical messengers between cells. Cytokines can stimulate or inhibit the growth and activity of various immune cells in response to the particular type of disease present. Examples of cytokines are the various interleukins and tumor necrosis factor