Posts Tagged ‘adequate response’

Notes on dosage
In this dictionary of drugs, the doses, unless otherwise stated, are average daily doses for adults, and are normally given as divided doses at suitable intervals. An indication is given of those few drugs that are taken as a single daily dose, or where
the dose is based on the surface area of the body expressed as square metres (ml).
When a dose range is indicated, a small initial dose is often followed by gradually increasing doses according to need and response, but with long-acting drugs care must be taken to avoid excessive dosage, as such drugs may then accumulate in the body and have toxic side-effects. It should be noted that the side-effects of a drug may prevent the administration of an optimum therapeutic dose, and a recommended dose is often a compromise between activity and toxicity. The gap is sometimes referred to as the ‘therapeutic window’, and the wider the gap the safer the drug.
Dosage is also influenced by the route of administration, as oral doses are normally larger than those given by intramuscular injection, and the latter are in turn larger than those given intravenously. The weight, age and sex of a patient may also have to be taken into account when assessing dosage. Renal and hepatic
-impairment may require an adjustment of dose, whereas if tolerance to a drug
develops, a larger dose may be required to evoke an adequate response. Dosage
also requires particular care during pregnancy if toxic effects on the fetus are to be avoided and, ideally, no drug should be given in pregnancy unless the need outweighs the risks.
Doses for infants also present problems. Their drug-detoxifying enzyme
systems and renal excretory capabilities are not fully developed although,
paradoxically, they have higher metabolic rates than adults, and so may sometimes require an apparently relatively high dose of a drug.

Doses for the elderly also frequently require modification, as their reduced renal efficiency may cause accumulation of the drug and increase susceptibility to toxic effects, unless reduced doses are given. Elderly patients are, in any case, more susceptible to nephrotic drugs generally. Hepatic disease may also increase drug toxicity as liver enzymes play a major part in drug metabolism, and severe liver disease may give rise to a drug toxicity that might not otherwise occur. Hyperlipidaemic drugs, fusidic acid and some antifungal agents of the ketoconazole type are examples of drugs best avoided in hepatic disease. Multiple therapy may also lead to an increased and not always appreciated incidence of drug toxicity. For further information on these important aspects of drug dosage, a book for nurses on drugs and pharmacology should be consulted.

Controlled drugs
Drugs likely to cause dependence and misuse are referred to as ‘controlled drugs’ (CDs), as they are subject to the strict prescription requirements of the Misuse of Drugs Act, 1971, and are distinguished in this book by a dagger t. They include opium, morphine, heroin (diamorphine), pethidine and other synthetic, potent analgesics/narcotics, dihydrocodeine injection, barbiturates (except intravenous anaesthetics) and amphetamines. Controlled drugs can be supplied only on receipt of a hand-written prescription from the prescriber, giving full details of the patient, the drug, the form and strength of the prescription to be dispensed, and the total amount to be supplied expressed in both words and figures. Certain weak preparations of some controlled drugs, such as Kaolin and Morphine Mixture for diarrhoea, with which misuse is unlikely, are exempt from control, and can be obtained without prescription.

vasodilators Traditional vasodilators used in the prophylaxis and treatment of angina include glyceryl trinitrate and other nitrates. They have a general effect on the venous system but newer and more selectively acting antihypertensive drugs are the betaadrenoceptor blocking agents represented by propranolol, and the calcium channel blocking agents such as nifedipine. Other vasodilator drugs are the alpha-adrenoceptor blocking agents (indorarnin, prazosin) and the ACE inhibitors (captopril). Cerebral vasodilators are represented by isoxsuprine. Peripheral vasodilators include cinnarizine and thymoxamine. See pages 114 & 148.
vasopressin A preparation of the blood pressure- raising and antidiuretic factors of the pituitary gland. It has been used in doses of 5-20 units twice daily by s.c. or i.m. injection in diabetes insipidus, but has been largely superseded by demopressin. (Pilressin).
vecuronitim A non-depolarizing muscle relaxant of the rocuronium type. It has a medium duration of action, with the advantage of not causing histamine release. Dose: 80-100fLgjkg1min initially, with supplementary doses as required. (Norcuron).
venlafaxine An antidepressant that inhibits the re-uptake of both serotonin and nor-adrenaline.
Dose: in depressive illness, 75 mg daily, rising if necessary after some weeks to 150 ing daily, or exceptionally to 375 mg daily. Prolonged treatment is necessary for an adequate response and reduce potential relapse. Reduced doses are given in hepatic disease and lite elderly. Care is necessary in epilepsy, and before and after morloaniine oxidase inhibator (MAGI) therapy. Many side-effects have been noted, but any skin reaction should be reported to the prescriber. (Ffcxor). See page 128 and Table 11.
Dose: 120-480 mg daily according to the condition and degree of response. In severe arrhythinias, 5-10 mg i.v. under ECG control. Contraindicated in bradycardia, heart failure and heart block. Side-effects include nausea, hypotension and heart block. It should be used with caution in a patient already receiving a betaadrenoceptor blocking agent. (Cordilox; Securon). See page 148 and Table 21.
vigabatrin A new anti-epileptic drug. GABA (a gamma aminobutyric acid) is an inhibitor of neurotransmission, and epileptic seizures may be linked with a GABA deficiency. Vigabatrin has an inhibitory action on the GABAmetabolizing enzyme, and so indirectly permits a rise in the brain level of GABA. It is used in the treatment of epilepsy not responding to other anticonvulsants. Dose: 2 g daily initially, with adjustments up to 4 g daily together with current antiepileptic therapy. Side effects are numerous, and include drowsiness, fatigue, dizziness and weight gain. Sudden withdrawal is inadvisable. (Sabril). See page 136 and Table 15.
viloxazine An antidepressant with the general action, uses and side-effects of amitriptyline, but with a reduced sedative activity. It is given in depression associated with apathy, and in the depression of epilepsy.
Dose: 150-400 mg daily. It may increase the action of phenytoin and antihypertensive agents. (Vivalan). See page 128 an(] Table 11.
vinblastine An alkaloid of periwinkle that has cytotoxic properties. It is used in the control of acute leukaemias, lymphomas and other malignant conditions, and in mycosis fungoides.
Dose: 100 ltrjkg weekly i.v., increased by 50 pg/ki; weekly, up to 500 µg/kg weekly according to response. Side-effects include myclosuppress.ion, neurotoxicity and abdominal disturbances. The drug should be handled with care as it is a tissue irritant. (Velbe). See page 122 and Table 8.
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verapamil A calcium channel blocking agent that reduces the movement ofcalciurn ions in cardiac tissues. It reduces the oxygen demand as well as the contractility of the myocardium, and it is used in angina, arrhythmias and hypertension.
vincristine A vinca alkaloid with the action and uses of vinblastine, but much less likely to cause myclodepression. It is used mainly in the treatment of acute
leukaemias in children, Hodgkin’s disease and other malignant lymphomas.

Neuromuscular side-effects may limit the dose. Other side-effects are abdominal disturbance and alopecia. The injection of the drug requires care as it is a tissue irritant. (Oncovin). See page 122 and Table 8.
vindesine A vinca alkaloid with an action similar to that of vincristine. It is used mainly in acute lyniphoblastic leukaemia in children, and in other malignant conditions not responding to treatment.
Dose: 3 nig/m` weekly by i.m. injection, subsequently increased up to 5 mg/in’ according to response. The side-effects are similar to those of other vinca alkaloids, but granulocytopenia may be a close-limiting factor. Extravasation should he avoided, as it may cause considerable local irritation. (Eldesine). See page 122 and fable R.
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vitamin D. Calciferol.
vitamin E The vitamin in the germ of wheat, rice and other grains. Deficiency States are uncommon, but may occur in cystic fibrosis and other conditions where fat absorption is impaired. It has been used empirically in many other
conditions, but its therapeutic value is questionable.
Dose: 5-15 ing daily. Now largely replaced by the synthetic form tocopherol.
vitamin K The vitamin concerned with the formation of prothrombin, and so with blood coagulation. Given as menadiol in haemorrhagic disorders, vitamin K, or phytomenadione has a similar but more rapid and sustained action. Of no value when the prothrombin level of the blood is adequate.
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vinorelbine A cytostatic drug of the vinca alkaloid type. It is used in non-small cell lung cancer and in advanced breast cancer resistant to other drugs.
Dose: 25-36 ing/inweekly by i.v.
infusion. Main side-effect is neutropenia. (Navelbine). See page 122.
vitamin A One of the vitamins obtained from fish-liver oils. A deficiency in the diet causes night-blindness, skin changes and a decreased resistance to infection. Dose: 2500-25 000 units daily.
vitamin B A group of water soluble vitamins obtained from yeast or rice polishings. The constituents include thiamine, riboflavine, nicotinic acid, pyridoxine, and small amounts of other factors.
vitamin B. Pyridoxine.
vitamin B,, Cynacobalamin. vitamin C Ascorbic acid.
warfarin A synthetic anticoagulant similar to phenindione, but with reduced side-effects and it is now the preferred drug. It is used mainly in deep-vein thrombosis and transient brain ischaernia, in doses based on the prothrombin time as
reported by the laboratory in terms of the International Normalized Ratio (INR). Dose: Pending INR report, 10 ing daily initially for up to 3 days. Haemorrhage is the main side-effect, and may require the use of phytornenadione to control the excessive response.
Whitfield’s ointment Benzoic acid 6%, salicylic acid 3%. Has keratolytic and fungicidal properties, and is used mainly for ringworm.
wool alcohols A water-in-oil emulsifying agent obtained from wool fat. It is used in many water-containing ointments, such as ointment of wool alcohols and hydrous ointment.
vitamin D The vitamin essential for the absorption of calcium and phosphorus and subsequent bone formation. Several forms of the vitamin are known, but it is used chiefly as calciferol. Vitamin D is activated in the liver and kidneys to more powerful derivatives such as calcitriol and alfacalcidol.
wool fat A pale yellow, waxy substance, also known as lanolin, obtained from sheep’s wool. It consists mainly of cholesterol-derivatives, and is a constituent of various water-in-oil emulsifying and emollient ointment bases. It may cause skin sensitization in some susceptible patients.

xamoterol A partial 0, adrenoceptor agonist with a cardiac stimulant action. It is given only in mild chronic heart failure to control exercise-induced symptoms. Dose: 400 ing daily. Side-effects are dizziness, headache and gastrointestinal disturbances. Contraindicated in severe heart failure, and care is necessary in asthmatic conditions. (Corwin). See page 141 and Table 18.
xipamide A long-acting diuretic and anti-hypertensive similar to chlorthalidone. Dose: in hypertension, 20 ing is given as a morning close: in oedematous states, 40-90 mg as a single dose, reduced later as necessary. (Diurexan). See page 148 and Table 21.
xylometazoline A sympathomimetic agent used as a nasal decongestant, and to relieve allergic conjuncfivitis as drops of 0.05-0.1%. Rebound congestion may be a side-effect.
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zalcitabineV An antiviral agent used in the suppressive treatment of AIDS patients who have become resistant to or have failed to respond to zidovudine therapy. Dose: 2.25 nig daily under expert supervision, as the drug has many side-effects including
., peripheral neuropathy. 0 livid).
zidovudine An antiviral agent effective against the human immunodeficiency virus (HIV) associated with the acquired immune deficiency syndrome (AIDS). It inhibits the enzyme reverse transcriptase and, by preventing the formation of viral DNIA, it inhibits viral development. Dose: 33 ing/kg4-hourly for some months. Side-effects include anaemia, neutropenia, nausea, fever and malaise. Liver-function tests are necessary during treatment. The chronic use of analgesics such as paracetamol may increase the risk of neutropenia. (Retrovir). See page 144 and “table 19.
zinc oxide A soft white powder widely used in dusting powders, ointments, pastes, etc., for its mild astringent and antiseptic properties. It is a constituent of Lassar’s paste, Unna’s paste, Calamine Lotion and similar preparations.
zinc sulphate Used as an astringent and stimulating lotion (1%) for indolent ulcers; and in conjunctivitis as eye drops (0.25%).
zinc undecenoate A white insoluble powder. Constituent of dusting powders and ointments for mycolic conditions.
zolmitriptan A serotonin receptor agonist used only in the treatment of acute migraine.
Dose: 2.5 ing as soon as possible after onset. .A second dose may be given not less than 2 hours later if symptoms persist. Vornig). See page 154 and Table 23.
zolpidem A mild hypnotic that acts by binding with a sub-group of benzodiazepine receptors. It has a rapid action, and is used in the short-term treatment of insomnia.
Dose: 10 mg. Side-effects are dizziness and gastrointestinal disturbance. (SI ilnoct). See page 152 and Table 22.
zopiclone A mild hypnotic that binds with a sub-group of benzodiazepine receptors, and may modulate the neurotransmitter GABA.
Dose: in insomnia and early awakening, 7.. —]S mg with initial doses of 3.75 mg for the elderly. A side-effect is a bitter or metallic after-taste. (Zimovane). See page 152.
zuclopenthixol A powerful tranquillizing drug with actions, uses and side-effects similar to those of chlorpromazine. It is of value in schizophrenia with agitation and aggression.
Dose: 20-30 mg or more up to 150 mg daily. For depot maintenance treatment, 100-200 mg or more by deep i.m. injection at intervals of 2-3 weeks, according to need and response. (Clopixol). See page 168.