Inh Health Dictionary

A method of applying drugs in a ?nely divided or gaseous state, so that, when breathed in, they may come into contact with the nose, throat and lungs. There are two chief means by which drugs are mingled with the air and so taken in by breathing: these are traditional steam inhalations, and modern aerosol devices which deliver a ?ne spray direct into the mouth. (See INHALANTS; INHALER.)... inhalation

Inhibition means arrest or restraint of some process e?ected by nervous in?uence. The term is applied to the action of certain inhibitory nerves: for example, the vagus nerve which contains ?bres that inhibit or control the action of the heart. The term is also applied generally to the mental processes by which instinctive but undesirable actions are checked by a process of self-control.... inhibition

A drug that curbs the action of an ENZYME in the blood controlling the production of carbonic acid or bicarbonate from CARBON DIOXIDE (CO2). Called carbonic anhydrase, the enzyme is present in ERYTHROCYTES and it has a key part in maintaining the acid-base balance in the blood. Inhibiting drugs include ACETAZOLAMIDE and DORZOLAMIDE, and these are used as weak DIURETICS to reduce the increased intraocular pressure in ocular hypertension or open-angle GLAUCOMA (see EYE, DISORDERS OF).... carbonic anhydrase inhibitor

The transfer of characteristics, traits and disorders from parents to children by means of

GENES carried in the CHROMOSOMES of the germ cells. (See GERM CELL; GENETIC CODE; GENETIC DISORDERS.)... inheritance

A mechanism for administering a drug in the form of a powder or aerosol. mainly used by patients with ASTHMA. Inhalers are basically of two types: aerosol, and dry-powder inhaler. The former delivers the drug as an aerosol spray when the patient presses the top of the canister containing the drug; the latter works by putting a drug capsule in the end of the chamber and, when the patient presses the top, the capsule is pierced and the drug released. A variety of ‘spacing devices’ are available to use with pressurised (aerosol) inhalers, providing metered doses. The space introduced between the inhaler and the mouth reduces the velocity of the aerosol and thus the impact it has on the oropharynx. More time is therefore allowed for evaporation of the propellant, with a greater concentration of drug particles being inhaled. Inhalers with larger spacing devices and a one-way valve are very e?ective and particularly useful for children and patients needing higher doses of the drug. (See INHALANTS; NEBULISERS.)... inhaler

These are drugs that inhibit the production of acid in the stomach by blocking a key enzyme system, known as the PROTON PUMP, of the parietal cells of the stomach. The drugs include omeprazole, lansoprazole and pantoprazole, and they are the treatment of choice for oesophagitis (erosion and stricture – see under OESOPHAGUS, DISEASES OF); for the short-term treatment for gastric ulcer (see under STOMACH, DISEASES OF) and DUODENAL ULCER; and, in combination with ANTIBIOTICS, for the eradication of Helicobacter pylori.... proton-pump inhibitors

The way in which a characteristic or an illness determined by the SEX CHROMOSOMES in an individual’s cells is passed on to the succeeding generation. Men have one X and one Y sex chromosome and women have two X chromosomes. Disorders that result from an abnormal number of sex chromosomes include KLINEFELTER’S SYNDROME, which affects only men, and TURNER’S SYNDROME, which affects mainly women. Recessive GENES on the X chromosome cause most other sex-linked characteristics; in women these may well be masked because one of their two X chromosomes carries a normal (dominant) gene. In men, who have just one X chromosome, no such masking occurs – so more men than women are affected by X-linked characteristics or diseases. (See also HEREDITY.)... sex-linked inheritance

See ANGIOTENSIN-CONVERTING ENZYME (ACE) INHIBITORS.... ace inhibitors

The ENZYME that converts angiotensin I to angiotensin II (see ANGIOTENSIN) is called angiotensin-converting enzyme. Angiotensin II controls the blood pressure and is the most potent endogenous pressor substance produced in the body; angiotensin I has no such pressor activity. Inhibition of the enzyme that converts angiotensin I to angiotensin II will thus have marked effects on lowering the blood pressure, and ACE inhibitors have a valuable role in treating heart failure when thiazides and beta blockers cannot be used or fail to work, especially after myocardial infarction (see HEART, DISEASES OF). Captopril was the ?rst ACE inhibitor to be synthesised: it reduces peripheral resistance by causing arteriolar dilatation and thus lowers blood pressure. Other drugs such as enalapril, lisinopril, cilazapril, quinapril and ramipril have since been developed. Some kidney disorders increase the production of angiotensin II and so cause HYPERTENSION.... angiotensin-convertingenzyme (ace) inhibitors

A group of drugs that stop the action of the ENZYME, aromatase. This enzyme converts androgens (see ANDROGEN) to OESTROGENS. If this conversion is inhibited, the concentrations of oestrogens in the body are reduced – so these drugs operate against tumours, such as breast cancer, that depend on oestrogen for their growth. Aromatase inhibitors include anastrazole and formestane, and they are usually prescribed as second-line treatment after TAMOXIFEN, the prime drug treatment for breast cancer.... aromatase inhibitors

This stands for cyclo-oxygenase 2 inhibitors – a class of drugs used in treating ARTHRITIS – of which the most well-used is celecoxib. Their main claim is that they are less likely to cause gastrointestinal disturbance than NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS). In 2001, the National Institute for Clinical Excellence (NICE) recommended that they should not be used routinely in rheumatoid arthritis or osteoarthritis but only in patients with a history of peptic ulcer or gastrointestinal bleeding. They should also be considered in persons over the age of 65 taking other drugs which could cause gastrointestinal bleeding, those who are very debilitated, and those who are taking maximum doses of NSAIDs. In 2005, rofecoxib was withdrawn because of concerns about cardiac side-effects.... cox-2 inhibitors

See COX-2 INHIBITORS.... cyclo-oxygenase-2 selective inhibitors

Substances that can be inhaled into the body through the lungs. They may be delivered in traditional form dissolved in hot water and inhaled in the steam, or as an aerosol – a suspension of very small liquid or solid particles in the air. The latter are now usually delivered by devices in which the aerosol is kept under pressure in a small hand-held cylinder and delivered in required doses by a release mechanism.

Aerosols Asthmatic patients (see ASTHMA) ?nd aerosol devices to be of value in controlling their attacks. They provide an e?ective and convenient way of applying drugs directly to the bronchi, thus reducing the risks of unwanted effects accompanying SYSTEMIC therapy. BRONCHODILATOR aerosols contain either a beta-sympathomimetic agent or ipratropium bromide, which is an ANTICHOLINERGIC drug.

ISOPRENALINE was the ?rst compound to be widely used as an aerosol. It did however stimulate beta1 receptors in the heart as well as beta2 receptors in the bronchi, and so produced palpitations and even dangerous cardiac arrhythmias. Newer beta-adrenoceptor agonists are speci?c for the beta2 receptors and thus have a greater safety margin. They include SALBUTAMOL, TERBUTALINE, rimiterol, fenoterol and reproterol. Unwanted effects such as palpitations, tremor and restlessness are uncommon with these, more speci?c preparations. In patients who get insu?cient relief from the beta-adrenoreceptor agonist, the drug ipratropium bromide is worth adding. Salmeterol is a longer-acting choice for twice-daily administration: it is not intended for the relief of acute attacks, for which shorter-acting beta2 stimulants such as salbutamol should be used. Salmeterol should be added to existing corticosteroid therapy (see CORTICOSTEROIDS), rather than replacing it.

Patients must be taught carefully and observed while using their inhalers. It is important for them to realise that if the aerosol no longer gives more than slight transient relief, they should not increase the dose but seek medical help.... inhalants

See REVERSE TRANSCRIPTASE INHIBITOR.... nucleoside reverse transcriptase inhibitor

The suppression of monoamine oxydase (flavin-containing amine oxydase). MAO is critical in modifying nerve-ending storage of certain mono­amines (in this case, epinephrine, norepinephrine and dopamine...another type of MAO works on histamines), and MAO inhibitor drugs were, along with tricyclics, the first wave of anti-depressants. The problem was that if you ate brie cheese or chopped chicken livers while taking the drugs you could get a nosebleed or cerebral aneurysm...a double adrenergic whammy, since some foods are also strongly MAO-inhibiting (at least functionally). Although most current manuals (Merck’s and Harrison’s among others) consider these first generation drugs as safer and preferable to the recent Prozac and such, fashion am fashion, with docs as much as patients. Most of the patients a doctor sees are People That See Doctors (most Americans have infrequent medical contact). Some come with clippings in hand, a few find out about new stuff before their doctor does (they only have ONE patient..themselves) and the pressure for gilt-edged newness is hard to resist all around. The only herb I know of with any consequential MAO inhibition is Hypericum, and its effect, although not to be ignored, is less than French semi-soft cheeses.... mao inhibition

These are drugs that destroy, or prevent the action of, monoamine oxidase (MAO). Monoamines, which include NORADRENALINE and tyramine, play an important part in the metabolism of the BRAIN, and there is some evidence that excitement is due to an accumulation of monoamines in the brain. MAO is a naturally occurring ENZYME which is concerned in the breakdown of monoamines. MAOIs were among the earliest ANTIDEPRESSANT DRUGS used, but they are now used much less than tricyclic and related antidepressants, or SELECTIVE SEROTONIN-REUPTAKE INHIBITORS (SSRIS) and related antidepressants, because of the dangers of dietary or drug interactions – and because MAOIs are less e?ective than these two groups.

An excessive accumulation of monoamines can induce a dangerous reaction characterised by high blood pressure, palpitations, sweating and a feeling of su?ocation. Hence the care with which MAOI drugs are administered. What is equally important, however, is that in no circumstances should a patient receiving any MAOI drug eat cheese, yeast preparations such as Marmite, tinned ?sh, or high game. The reason for this ban is that all these foodstu?s contain large amounts of tyramine which increases the amount of certain monoamines such as noradrenaline in the body. (See MENTAL ILLNESS.)

There are also certain drugs, such as AMPHETAMINES and PETHIDINE HYDROCHLORIDE, which must not be taken by a patient who is receiving an MAOI drug. The MAOIs of choice are phenelzine or isocarboxazid because their stimulant effects are less than those of other MAOIs, making them safer.... monoamine oxidase inhibitors (maois)

Exogenously, a PGE inhibitor like aspirin, and usually intended to lessen joint inflammation and uterine spasms.... pg inhibitor

A new group of drugs which, in combination with antiviral agents, are used to treat AIDS (see AIDS/HIV). They inhibit the activity of PROTEASE, an enzyme produced by HIV, and which breaks down proteins. The drugs have recently been introduced: those in use are indinavir, nel?navir, ritonavir and saquinavir.... protease inhibitors

An agent that prevents the action of the viral ENZYME, REVERSE TRANSCRIPTASE, so disrupting the virus’s colonisation of its target host. The reverse transcriptase inhibitor ZIDOVUDINE is used (in combination with other agents) to treat HIV infection.... reverse transcriptase inhibitor

These ANTIDEPRESSANT DRUGS have few antimuscarinic effects (see ANTIMUSCARINE), but do have adverse effects of their own – predominantly gastrointestinal. They are, however, much safer in overdose than the tricyclic antidepressants, which is a major advantage in patients who are potentially suicidal. Examples are citalopram, used to treat panic disorders, as well as depressive illness; FLUOXETINE; and PAROXETINE. (See also MENTAL ILLNESS.)... selective serotonin-reuptake inhibitors (ssris)

Smoke is made up of small particles of carbon in hot air and gases. The particles are covered with organic chemicals and smoke may also contain carbon monoxide and acids. When smoke is inhaled, the effects on breathing may be immediate or delayed, depending upon the density of smoke and its composition. Laryngeal stridor (obstruction of the LARYNX), lack of oxygen and PULMONARY OEDEMA are life-threatening symptoms that require urgent treatment. Immediate removal of the victim from the smoke is imperative, as is the administration of oxygen. The victim may require admission to an intensive-care unit.... smoke inhalation

Herbs containing essential oils are sometimes used as inhalations. 1oz (30g) herb is infused in 2 pints (one and a quarter litres) boiling water for 15 minutes, strained, and the steam inhaled with the aid of a towel above the head. Soothing to irritable and sensitive mucous surfaces. Anti- microbial effects on colds, whooping cough, croup, laryngitis, coryza, asthma and early stages of fevers. To relieve spasm of bronchioles: Lobelia, Stramonium, Eucalyptus, Aloe Vera.

Important inhalants: Eucalyptus, Thyme, Hyssop, Rosemary, Lavender, Chamomile, Mint, Tea Tree. Aromatherapy offers oils of the above herbs: 6-12 drops floated on the surface of 2 pints boiling water after being allowed to stand 3 minutes. See: FRIAR’S BALSAM. TEA TREE.

Alternative method. In place of a basin use an aluminium hot water bottle into which boiling water is poured. Add few drops Friar’s Balsam, Olbas, or essential oil. Insert a large funnel into which the mouth and nose are placed to breathe the vapour. Stop up any free space in the neck of the bottle with a tissue. Camphorated oil. 4 teaspoons to litre boiling water. Inhale steam with aid of a towel over head.

Inhalant Salve for nasal congestion and frontal sinusitis. Oil Pine 1ml; Oil Eucalyptus 2ml; Oil Peppermint 2ml; Vaseline to 30 grams. Melt the Vaseline. Add oils. Stir until cold. For direct use or inhaled from boiling water. (F. Fletcher Hyde, FNIMH)

Note: Inhalation: also through a tissue, steam or air-diffuser. Odours act upon the sense of smell and influence mucous secretion of the respiratory organs. ... inhalations

A group of vasodilator drugs used to treat heart failure, hypertension, and diabetic nephropathy. (angiotensin converting enzyme) inhibitors are often prescribed with other drugs such as diuretic drugs or betablocker drugs. Possible side effects include nausea, loss of taste, headache, dizziness, and dry cough.... ace inhibitor drugs

A group of drugs that are used in the treatment of mild to moderate dementia due to Alzheimer’s disease, in which there is a deficiency of the neurotransmitter acetylcholine in the brain.

Drugs such as donepezil and rivastigmine work by blocking the action of acetylcholinesterase, the enzyme in the brain responsible for the breakdown of acetylcholine.

This raises acetylcholine levels, and, in half of all patients, the drugs slow the rate of progression of dementia.

They have no effect on dementia due to other causes, such as stroke or head injury, however.

Common side effects include nausea, dizziness, and headache.

Rarely, difficulty in passing urine may occur.... acetylcholinesterase inhibitors

A group of non-steroidal anti-inflammatory drugs (NSAIDs) that cause less stomach irritation as a side effect than other NSAIDs. Examples of -2 inhibitors include celecoxib and rofecoxib.... cox-2 inhibitor drugs

Drugs used in the treatment of Parkinson’s disease.

The 2 main dopa-decarboxylase inhibitors, co-beneldopa and co-careldopa, are a combination of levodopa and benserazide and levodopa and carbidopa respectively.

These drugs prevent levodopa from being activated except within the brain, which reduces the incidence of side effects such as nausea and vomiting.... dopa-decarboxylase inhibitors

Also known as MAOIs, one of the 3 main types of antidepressant drug.

They work by preventing the breakdown of certain neurotransmitters by the enzyme monoamine oxidase.

The increased levels of neurotransmitters that result are associated with improved mood.

Common drugs include phenelzine and isocarboxazid.

All MAOIs interact with certain other drugs and foods such as cheese and red wine; but moclobemide is known as a reversible , which makes the adverse reactions less likely to occur.... monoamine oxidase inhibitors

A class of drugs used in the treatment of diseases, including HIV infection, that are caused by retroviruses. The drugs affect the ability of the virus to reproduce by blocking reverse transcriptase, a key enzyme. Drugs include lamivudine, zidovudine (AZT), efavirenz, and stavudine.... reverse transcriptase inhibitors

(SSRIs) A relatively new class of drugs that are used to treat depression.

They work by blocking the reabsorption of the neurotransmitter serotonin following its release in the brain.

The increased serotonin levels that result are associated with improved mood.

Common drugs in this group include fluoxetine and sertraline.

SSRIs are usually taken orally once a day; it may take 1–3 weeks for any noticeable improvement in symptoms.

SSRIs usually produce fewer side effects than other types of antidepressant drug.

However, they may cause diarrhoea, nausea, restlessness, and anxiety.... selective serotonin reuptake inhibitors

Lack of sexual desire or of the ability to become physically aroused during sexual activity.... sexual desire, inhibited

A method of relieving some of the symptoms of colds, sinusitis, and laryngitis by breathing in hot vapour from a bowl of hot water. The moisture loosens secretions in the nose and throat, making them easier to clear.... steam inhalation

angiotensin-converting enzyme inhibitor: any one of a group of drugs used in the treatment of raised blood pressure and heart failure. ACE inhibitors act by interfering with the action of the enzyme that converts the inactive *angiotensin I to the powerful artery constrictor angiotensin II. The absence of this substance allows arteries to widen and the blood pressure to drop. Possible side-effects include weakness, dizziness, loss of appetite, and skin rashes.... ace inhibitor

any one of a class of drugs that block the action of acetylcholinesterase (see cholinesterase), an enzyme that quickly breaks down the neurotransmitter acetylcholine. This neurotransmitter is central to the functional interconnection between nerve cells in the outer layer (cortex) of the brain; the early impairment of cognitive function found in Alzheimer’s disease is associated with a reduction in acetylcholine levels. By inhibiting acetylcholine breakdown, acetylcholinesterase inhibitors have been found helpful in slowing down the rate of cognitive decline in mild to moderate dementia; they do not halt the progress of the disease. The group includes donepezil, galantamine, and rivastigmine... acetylcholinesterase inhibitor

any member of a group of *oral hypoglycaemic drugs, including acarbose (Glucobay), used for treating type 2 *diabetes mellitus. They reduce the breakdown and absorption of carbohydrates in the intestine by blocking the action of an important enzyme (?-glucosidase) in this process. Side-effects include flatulence and diarrhoea.... alpha-glucosidase inhibitor

an agent that prevents the development of new blood vessels (*angiogenesis) by inhibiting the action of *vascular endothelial growth factor (it is also known as anti-VEGF). Angiogenesis inhibitors are used as anticancer drugs, since growing cancers have a greater need for blood supply than normal tissue and must develop new blood vessels before progressing beyond a very small size. They include *aflibercept, *bevacizumab, and *thalidomide. Because of their action, some of these drugs are used in the treatment of wet age-related *macular degeneration.... angiogenesis inhibitor

any one of a class of drugs used in the treatment of early and advanced oestrogen-dependent breast cancer in postmenopausal women. These drugs act by inhibiting the action of aromatase, an enzyme that promotes the conversion of testosterone to oestradiol. They therefore reduce oestrogen levels, which can be helpful in the control of oestrogen-dependent tumours. Aromatase inhibitors include anastrazole, exemestane, and letrozole. Side-effects include symptoms of oestrogen deficiency (e.g. hot flushes), nausea and vomiting, and headache.... aromatase inhibitor

drugs that act by inhibiting the calcium-dependent protein *phosphatase calcineurin, an enzyme that initiates a sequence of events that bring about activation of T *lymphocytes. The group includes *ciclosporin and *tacrolimus, which are major maintenance immunosuppressants used in transplantation. Topical calcineurin inhibitors (e.g. tacrolimus, pimecrolimus [Elidel]) are used in the treatment of eczema when topical steroids have failed or are contraindicated. Stinging is a common transient side-effect, and reactivation of infections may occur.... calcineurin inhibitors

any one of a group of anti-inflammatory drugs (see NSAID) that selectively block the action of the enzyme cyclo-oxygenase 2 (COX-2), which mediates the production of *prostaglandin at sites of inflammation, especially in joints; they are less likely to inhibit COX-1, which controls the production of prostaglandin in the stomach (where it is involved in the production of protective mucus), and therefore less likely than nonselective NSAIDs to cause peptic bleeding or ulceration. COX-2 inhibitors are used in the treatment of arthritis, acute gout, and moderate or severe pain. They include *celecoxib and etoricoxib. However, because their use is associated with an increased incidence of heart attack and stroke, COX-2 inhibitors should be taken only by those who are not at risk of developing these conditions and who have a high risk of developing peptic ulceration. Other side-effects include fluid retention (oedema), intestinal upset, dizziness, insomnia, and sore throat.... cox-2 inhibitor

(cytokine modulator) any one of a group of agents that inhibit the activity of cytokines, especially *tumour necrosis factor alpha (TNF-?). They include *infliximab, *etanercept, and *adalimumab, known as anti-TNF drugs, which are used as *disease-modifying antirheumatic drugs and to treat inflammatory bowel disease.... cytokine inhibitor

the inheritance of characters controlled by genes present in the cell cytoplasm rather than by genes on the chromosomes in the cell nucleus. An example of cytoplasmic inheritance is that controlled by mitochondrial genes (see mitochondrion).... cytoplasmic inheritance

any of various drugs that interfere with the conversion of folate to its active form in the body. They include *pyrimethamine, *trimethoprim, and *methotrexate. When such drugs are necessary, folate deficiency is treated with *folinic acid rather than folic acid.... dihydrofolate reductase inhibitor

any one of a class of antiviral drugs that inhibit the action of DNA polymerase enzymes, which are used by viruses to form their own DNA. These drugs prevent, to a varying degree, the reproduction of viruses. They include *aciclovir, *foscarnet, *ganciclovir, and *valaciclovir.... dna polymerase inhibitor

a group of *oral hypoglycaemic drugs used in the treatment of type 2 diabetes mellitus. Through inhibiting the enzyme dipeptidyl peptidase-IV they enhance the action of *glucagon-like peptide-1. Five drugs in this group are currently licensed for use in the UK: sitagliptin, vildagliptin, saxagliptin, linagliptin, and alogliptin.... dpp-iv inhibitors

see thrombophilia.... inherited thrombophilias

n. see activin.... inhibin

n. a substance that prevents the occurrence of a given process or reaction. See also MAO inhibitor.... inhibitor

(MAOI) a drug that prevents the activity of the enzyme *monoamine oxidase (MAO). MAO inhibitors include phenelzine, isocarboxazid, and tranylcypromine. These drugs are irreversible inhibitors of monoamine oxidase A, whose use as antidepressants is now restricted because of the severity of their side-effects. These include interactions with other drugs (e.g. ephedrine, phenylephrine) and with foods or drinks containing *tyramine (e.g. cheese or red wine) to produce a sudden and dangerous increase in blood pressure. *Moclobemide is a reversible inhibitor of monoamine oxidase A (RIMA), with less severe side-effects. See also selegiline.... mao inhibitor

a drug that blocks the action of the PARP enzyme, which is required for *DNA repair in cancer cells with faulty *BRCA1 and BRCA2 genes. These drugs are used in the treatment of cancer in patients with BRCA1 or BRCA2 mutations. They are also undergoing trials to see if they are useful in the treatment of other cancers.... parp inhibitor

any one of a class of drugs used in the treatment of HIV infection and *AIDS. Used in combination with other *antiretroviral drugs, they act by inhibiting the action of protease, an enzyme produced by HIV that cleaves two precursor proteins into smaller fragments. These fragments are required for viral growth, infectivity, and replication. Protease inhibitors include atazanavir, indinavir, lopinavir and ritonavir (which are used in combination), saquinavir, and tipranavir. Side-effects include nausea, vomiting, diarrhoea, and rashes; these drugs are also associated with hyperglycaemia and *lipodystrophy. See also boceprevir.... protease inhibitor

a drug that reduces gastric acid secretion by blocking the *proton pump. Proton-pump inhibitors include esomeprazole, lansoprazole, *omeprazole, pantoprazole, and rabeprazole sodium; they are used for treating gastro-oesophageal reflux disease, peptic ulcer, and acid hypersecretion associated with *gastrinoma.... proton-pump inhibitor

receptor activator of nuclear factor kappa B ligand inhibitor: an agent that works by inhibiting the development of *osteoclasts and bone resorption, thus minimizing bone loss and the potential for fractures in those with postmenopausal osteoporosis and bone metastases.... rankl inhibitor

see SNRI.... selective serotonin and noradrenaline reuptake inhibitor

a class of *oral hypoglycaemic drugs for use in the treatment of type 2 diabetes mellitus. Sodium/glucose cotransporter 2 (SGLT-2) plays the largest role in glucose reabsorption in the kidney. Inhibition of SGLT-2 leads to an increase in the loss of glucose in the urine, a reduction in blood glucose levels, and a modest degree of weight loss over time due to the increased calorie loss. Two drugs in this class are currently licensed for use in the UK: dapagliflozin (Forxiga) and canagliflozin (Invokana).

SGOT (serum glutamic oxaloacetic transaminase) see aspartate aminotransferase.

SGPT (serum glutamic pyruvic transaminase) see alanine aminotransferase.... sglt-2 inhibitors

see calcineurin inhibitors.... topical calcineurin inhibitors

any one of a class of *cytotoxic drugs that work by blocking the action of topoisomerase enzymes, which promote the uncoiling of the DNA double helix, a necessary preliminary to replication. Topoisomerase I inhibitors include irinotecan, used for treating advanced colorectal cancer (especially in combination with *fluorouracil); and topotecan, given for treating advanced ovarian cancer, relapsed small-cell lung cancer, and recurrent cervical cancer. Side-effects include delayed but severe diarrhoea and reduction in blood-cell production by the bone marrow. Topoisomerase II inhibitors include *etoposide and *doxorubicin.... topoisomerase inhibitor

any one of a class of drugs that interfere with cell growth in a variety of different ways by inhibiting the action of tyrosine kinases. This family of enzymes, which occur both within cells and as components of cell-membrane receptor sites, have an important role in cell division and cell growth. Many tumour cells have been shown to have both intracellular enzymes and extracellular receptor sites, and a variety of anticancer agents have been developed to inhibit enzyme activity at these sites. Among these drugs are *imatinib, dasatinib, and nilotinib, used for treating chronic myeloid leukaemia; *sunitinib, for treating renal cell carcinoma; and erlotinib, for treating pancreatic cancer and non-small-cell lung cancer. See also epidermal growth factor receptor.... tyrosine kinase inhibitor