1. Introduction: Selecting and Prescribing Drugs

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旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 1. Introduction: Selecting and Prescribing Drugs 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Outline: Reasons for drug selection. Major indications Approved indications. Pharmacokinetic considerations. Contraindications and warnings. Adverse effects. Overdose Toxicity Cost of Drugs How should the prescriber choose a drug when presented with a situation in which the disease or the treatment is unfamiliar? This book attempts to provide the basis for that process, using several criteria. The section on drug selection follows (use the PgDn key to proceed and PgUp to come back). (PgDn key for more text) To jump to a new topic (in < >) move the highlight with the arrow keys at the right side of the keyboard, then press enter. For example, the mechanics of prescribing and ordering drugs are described in . I. DRUG SELECTION Factors that facilitate selection of a drug that is likely to be beneficial include: knowledge of the pathophysiology of the disease being treated; a set of rational goals of therapy; and the published reports of successful use of the candidate drugs. Equally important is information regarding the potentially detrimental effects of the candidate agents such as: con- traindications and warnings -- potentially dangerous situations that have been explicitly listed; adverse effects, taken to mean those unwanted effects that occur at or close to the recommended doses; overdose effects, ie, those effects that may occur if the patient or someone else with access to the prescription takes a grossly excessive dose; interactions with other drugs; and finally, economic cost to the patient. Based on the above list, the chapters in this book are con- structed on the following pattern: (PgDn key for more text) * Pathophysiology: The disease setting in which the drug is to be used and the underlying disease mechanism, if known. * Therapeutic Rationale: The major goals of pharmacologic therapy, and how these goals relate to the pathophysiology of the disease. * Mechanisms: The mechanisms by which the drugs act; how these mechanisms relate to the therapeutic rationale. * Major indications: The diseases for which the drug is known or thought to be effective. Both labeled (FDA approved) and un- labeled indications that are pertinent to the disease state are mentioned. Unlabeled uses are uses of a drug that are not specifically approved by the FDA. Such absence of approval may mean that at the time of the original submission of the New Drug Application there was no evidence to suggest that the drug would be useful in the unlabeled indication. Alternatively, the manufacturer may have decided that it would be too expensive to obtain the evidence necessary to support a claim of efficacy in this indication. Unlabeled uses are medically valid and legal if they are supported by the literature and the best judgement of the medical com- munity. This book specifies many known unlabeled indications for individual drugs. (PgDn for more text) * Other Indications: Indications for the use of the drug that are not directly pertinent to the disease under discussion. * Pharmacokinetics: Major aspects of absorption and elimination that may influence the selection of drug, eg, oral bioavailability and route of excretion. This information is supplemented by additional pharmacokinetic facts, especially half-life, in the tables that appear in every chapter. These tables contain listings of the major dosage forms available for each of the drugs in the group under discussion. * Contraindications and Warnings: Conditions that, in the opinion of the authors of this book or other literature, con- stitute reasons for considering an alternate drug. Most manufacturers ``over-report'' contraindications and warnings to protect against legal suits. Contraindications may be con- sidered ``very important'' while warnings are merely ``possibly important.'' In both cases, the nature of the con- traindication or warning must be weighed against the specific circumstances of the patient. (PgDn key for more text) * Adverse Reactions: Undesirable effects (in the context of the condition being treated) that may occur in patients taking ordinary therapeutic doses of the drug. They cannot be con- sidered as certain to occur or even probable in any given patient; most of them have an incidence of less than 1% (the incidence is given in some of the chapters of this book) but are listed because they have been reported. This has the desirable effect of raising the prescriber's index of suspicion if the patient complains of new symptoms. Note that these undesired effects may be considered therapeutic in other clinical contexts, eg, sedation caused by antihistamines is an adverse effect in hay fever treatment but a therapeutic goal in the treatment of insomnia. (PgDn key for more text) * Overdose Toxicity: This section lists those actions that are usually seen only at doses or blood levels higher than the recommended therapeutic dose or level and are clearly un- desirable in all cases. For drugs with low therapeutic in- dices, this dose range may overlap the therapeutic range. Furthermore, for some drugs, the most serious effects are direct extensions of the therapeutic action being sought. In these cases, the sections on Adverse Effects and on Overdose Toxicity may be combined. Where specific treatment is pos- sible, eg, through the use of an antidote, information is provided on the management of overdose toxicity. For all cases of drug overdosage, the general rules of vital signs support, detoxification, and symptomatic therapy (``conserva- tive management,'' see Chapter 24) apply. * Interactions: This section provides information regarding the most common and most important interactions with other drugs. * Drugs of Special Importance, Drug Selection: A listing of most useful agents of the group. In some chapters, especially haz- ardous drugs and obsolete drugs are also mentioned here, so that they may be avoided. (PgDn key for more text) * Related Drugs: Members of other drug groups that are similar in some way, eg, chemical characteristics that result in cross allergenicity. * References: A listing of recent papers or book chapters that bear on the clinical choice of a drug for the disease. * Cost information: Unfortunately, the variability in the retail cost of drugs is so great that it is not practical to provide detailed cost predictions. Listings of average wholesale prices are available (Drug Topics RedBook), however, and for a few drug groups, such as antacids, anti-inflammatory agents, and certain antibiotics, in which relative cost can be of great importance in selecting a drug, the average wholesale price has been provided in the table of doses. It must be realized, however, that this information is subject to change and represents only the price to the pharmacy, not the patient. Before prescribing a large quantity of any drug, even one expected to be relatively cheap, the responsible prescriber will determine what the actual cost to the patient will be. (PgUp key to go to previous screen, Home to go to start)

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