120 to 270 mg per kg of body weight, administered over a few days. In a few instances, severe and fatal congestive heart failure has occurred. Nausea, vomiting, and temporary hair loss occur frequently. Bone-marrow toxicity that causes reductions in white blood cell count are common. Reductions in the number of platelets and red blood cells develop occasionally but are reversible after therapy stops. Finally, severe toxicity to the lungs or kidneys also occurs occasionally. Rarely, allergic reactions, and death have been reported.
cycloserine A broad-spectrum antibiotic that has been used in combination with other drugs in treating tuberculosis. It is contraindicated in patients with epilepsy and in those with depression or anxiety. (Trade name is Seromycin.)
cyclosporine An immunosuppressive drug used to prevent graft rejection in organ transplants. The drug acts specifically against t cells in the early stages of activation. Reports on the use of this drug in people with HIV are contradictory. Also called cyclosporine A, CsA for short.
cyst A closed sac or pouch, with a definite wall, that contains fluid, semifluid, or solid material. It is usually an abnormal structure resulting from developmental abnormalities, obstruction of ducts, or from a parasitic infection. See Bartholin's duct.
cysteamine Used for treatment of a rare genetic kidney disease in children. May work with AZT in preventing HIV from reproducing.
cysteine An amino acid, one of three components of glutathione (gsh). See n-acetylcysteine.
cystitis An infection of the urinary bladder, usually occurring secondary to ascending urinary tract infections. Associated organs (kidney, prostate, urethra) may be involved. May be acute (with frequent and painful urination) or chronic (secondary to another lesion) possibly with pyuria as the only symptom. Antibiotics are useful in treating the infection, but more definitive therapy will be required if the basic cause is a renal calculus (kidney stone) or other obstruction in the urinary tract.
cytarabine A drug compound (cytosine arabi-noside) originally developed as an antileukemic agent and now being used in treating herpes virus hominis infections that cause either keratitis or encephalitis. The first well-controlled clinical trial found that treatment offers no benefit to patients with PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPA-
thy (PML). These results came as no surprise, since there were reports that patients treated with cytarabine die faster than those who received no treatment. There has been at least one published case of cytarabine causing PML in a person with cancer by suppressing the immune system. Also called ARA-C.
cytidine A nucleoside of cytosine. Lamivudine (3TC) and dideoxycytidien (ddC) are analogs of cytidine.
cytochrome P450 one of the many different known cytochrome enzymes living in organisms, cytochrome P450 enzymes are a family of enzymes in the liver that metabolize drugs and other fat-soluble substances. The cytochrome P450 enzymes are found in virtually all animals and vary widely in number. They are most active in tissues that have most frequent contact with external materials—the liver, lung, skin, gut, and kidneys—but are found throughout the human body. It is not known how the cytochrome P450 enzymes recognize the chemicals, including drugs, steroids, and other compounds, on which they act. It is known that these chemicals are sparingly soluble in water and that they tend to accumulate in the membranes and water-free structures within cells and tissues. The cytochrome P450 enzymes metabolize these substances in these locations, rendering them more soluble in water and less toxic. Solubilized and detoxified, these compounds can then be dissolved in the blood and transported to the kidneys for elimination. Certain medications, such as RIToNAVIR, inhibit some of the P450 enzymes, in particular P450 3A4 (also called CYP3A4), affecting the liver's ability to break
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