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Macrophage: a large scavenger cell that ingests degenerated cells and foreign organisms. Macrophages exist in large numbers throughout the body and contribute to the development of acquired immunity by acting as antigen presenting cells (see). They also ingest and destroy foreign matter coated with antibody Macrophages can be infected by the HIV virus.

Macula: the pigmented central area or .yellow spot. of the retina that is adjacent to the optic nerve. It is the most sensitive area of the retina and contains the fovea, a depressed region that is responsible for detailed central vision.

Magnetic Resonance Imaging (MRI): a non-invasive, nonx-ray diagnostic technique based on the magnetic fields of hydrogen atoms in the body. MRI provides computer-generated images of the body.s internal tissues and organs.

Maintenance Therapy: extended drug therapy, usually at a diminished dose, administered after a disease has been brought under control. Maintenance therapy is utilized when a complete cure is not possible, and a disease is likely to recur if therapy is halted.

Major Histocompatibility Complex (MHC): two classes of molecules on cell surfaces. MHC class I molecules exist on all cells and hold and present foreign antigens to CD8 cytotoxic T-lymphocytes if the cell is infected by a virus or other microbe. MHC class II molecules are found on the immune system.s antigen presenting cells (see) and display antigen to activate CD4 T-helper cells.

Malabsorption: inability of the intestines to absorb food, drug or any substance needed to maintain good health.

Malaise: a vague feeling of discomfort or uneasiness, often the result of infection or a drug.s side effects.

Malignant: refers to cells or tumors growing in an uncontrolled fashion. Such growths may spread to and disrupt nearby normal tissue or reach distant sites via the bloodstream. By definition, cancers are always malignant, and the term malignancy implies cancer.

Manifestation: the outward sign that an illness is present - a symptom or condition.

Mast Cell: an immune system cell filled with granules of inflammatory chemicals such as histamine. This cell is believed to play a leading role in generating the symptoms of allergy.

Medulla: the inner portion of an organ.

Medicinal chemistry is a chemistry-based discipline, also involving aspects of biological, medical and pharmaceutical sciences. It is concerned with the invention, discovery, design, identification and preparation of biologically active compounds, the study of their metabolism, the interpretation of their mode of action at the molecular level and the construction of structure-activity relationships.

Metabolism comprises the entire physical and chemical processes involved in the maintenance and reproduction of life in which nutrients are broken down to generate energy and to give simpler molecules (catabolism) which by themselves may be used to form more complex molecules (anabolism). In case of heterotrophic organisms, the energy evolving from catabolic processes is made available for use by the organism. In medicinal chemistry the term metabolism refers to the biotransformation of xenobiotics and particularly drugs. (See also Biotransformation; Xenobiotic).

Metabolite is any intermediate or product resulting from metabolism.

Me-too drug is a compound that is structurally very similar to already known drugs, with only minor pharmacological differences.

Micelle is the association of amphiphilic molecules with each other into structures having the hydrophobic portions of the molecules separated from the aqueous solvent by a self-generating hydrophobic mellieu, while the polar groups face the solvent and hydrogen bond with the water molecules.

Molecular graphics is the visualization and manipulation of three-dimensional representations of molecules on a graphical display device.

Molecular modeling is a technique for the investigation of molecular structures and properties using computational chemistry and graphical visualization techniques in order to provide a plausible three-dimensional representation under a given set of circumstances.

Monoclonal Antibody: an antibody produced by laboratory cultures of a single cell line. The antibodies all bind with the same antigen on a bacteria, virus or cancer cell and are supposed to evoke an immune response.

Monocyte: a large white blood cell that is the precursor of macrophages.

Mutagen is an agent that causes a permanent heritable change (i.e., a mutation) into the DNA (deoxyribonucleic acid) of an organism.

Mutual prodrug is the association in a unique molecule of two, usually synergistic, drugs attached to each other, one drug being the carrier for the other and vice versa.

Myelosuppression: the suppression of bone marrow activity, causing decreased production of red blood cells (anemia) or white blood cells (leukopenia). Myelosuppression is an effect of some drugs, such as AZT.

Myelitis: inflammation of either the spinal cord or the bone marrow.

Myelopathy: any disease affecting the spinal cord.

Myelotoxic: destructive to bone marrow.

Myocardial: refers to the heart.s muscle mass.

Myopathy: progressive muscle weakness.

NCE abbreviation for New Chemical Entity.

NDA Abbreviation for New Drug Application.

Neurologic relating to nervous system, including the brain.

Neuropathy a disease of the nerves. See Peripheral Neuropathy.

Neutropenia a shortage of neutrophils in the blood.

Nerve Growth Factor (NGF a naturally produced substance that has many roles in the maintenance of nerves and nerve cells, especially sensory ones. Synthetic, recombinant NGF is a proposed therapy for HIV- and drugassociated neuropathies.

New Chemical Entity is a compound not previously described in the literature.

Non-classical isostere has same meaning as Bioisostere.

Non-Hodgkin.s Lymphorna a lymphoma made up of B-cells and characterized by nodular or diffuse tumors. It may appear in the stomach, liver, brain and bone marrow of people with HIV. After Kaposi.s sarcoma, NHL is the most common opportunistic cancer in people with AIDS.

Nucleic acid is a macromolecule composed of linear sequences of nucleotides that perform several functions in living cells, e.g., the storage of genetic information and its transfer from one generation to the next DNA (deoxyribonucleic acid), the expression of this information in protein synthesis (mRNA, tRNA) and may act as functional components of subcellular units such as ribosomes (rRNA). RNA (ribonucleic acid) contains D-ribose, DNA contains 2-deoxy-D-ribose as the sugar component.

Nucleoside is a compound in which a purine or pyrimidine base is bound via a N-atom to C-1 replacing the hydroxy group of either 2-deoxy-D-ribose or of D-ribose, but without any phosphate groups. (See also nucleotide). The common nucleosides in biological systems are adenosine, guanosine, cytidine, and uridine (which contain ribose) and deoxyadenosine, deoxyguanosine, deoxycytidine and thymidine (which contain deoxyribose).

Nucleotide is a nucleoside in which the primary hydroxy group of either 2-deoxy-D-ribose or of D-ribose is esterified by orthophosphoric acid. (See also nucleoside).

Off-Label use: use of a drug for a disease or condition other than the indication for which it was approved by the FDA.

Oligonucleotide is an oligomer resulting from linear sequences of nucleotides.

Oncogene is a normal cellular gene which, when inappropriately expressed or mutated, can transform eukaryotic cells into tumor cells.

Open-Label Trial: a study in which both researchers and participants know what drug a person is taking and at what dose.

Orphan drug is a drug for the treatment of a rare disease for which reasonable recovery of the sponsoring firm.s research and development expenditure is not expected within a reasonable time. The term is also used to describe substances intended for such uses.

Oxidative Stress: a highly oxidized environment within cells where cells are forced into a highly activated state due to loss of control of their regulatory systems.