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INTRODUCTION

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This chapter will be most useful after having a basic understanding of the material in Chapter 48, General Principles of Antimicrobial Therapy in Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 12th Edition. Neither Mechanisms of Action nor Clinical Summary Tables are included in this chapter because this information is provided in subsequent chapters.

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In addition to the material presented here, Chapter 48 of the 12th Edition contains:

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  • A detailed discussion of the pharmacokinetic basis for antimicrobial therapy

  • A thorough discussion of the types and goals of antimicrobial therapy

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LEARNING OBJECTIVES

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  • Describe the pharmacokinetic basis of antimicrobial therapy.

  • Identify the importance of susceptibility testing of antimicrobial agents.

  • Identify the factors that form the basis for selection of an antimicrobial dose and dosing schedule.

  • Describe the types and goals of antimicrobial therapy.

  • Identify the mechanisms of resistance to antimicrobial agents.

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CLASSIFICATION OF ANTIMICROBIAL AGENTS

  • The first broad classification of antimicrobial agents is according to the microorganisms they are active against: antibacterial, antiviral, antifungal, antiparasitic.

  • Further classification of an antibiotic is based on:

    • The class and spectrum of the microorganisms it kills

    • The biochemical pathway it interferes with

    • The chemical structure of its pharmacophore (the chemical moiety of the drug that binds to a microbial receptor)

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DRUGS INCLUDED IN THIS CHAPTER

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The pharmacology of specific drugs is not included in this chapter. The drugs presented in the cases are used as examples to illustrate various aspects of antimicrobial therapy; the specific pharmacology of these drugs is presented in the subsequent chapters of this section.

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CASE 34-1

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A 34-year-old woman has a diagnosis of pneumococcal meningitis. The pathogen is determined to be sensitive to penicillin and she is being treated with high-dose penicillin.

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  1. How does the chemical nature of a drug affect its penetration into various anatomic compartments such as the brain?

    An important factor is the drug’s lipid solubility or its octanol:water partition coefficient. The higher the octanol:water partition coefficient, the more likely it is to penetrate physical barriers erected by layers of cells. The more charged a drug molecule, and the larger it is, the poorer its penetration across physical barriers.

  2. What is unique about the brain in terms of drug penetration?

    The central nervous system (CNS) is guarded by the blood–brain barrier. The movement of antibiotics across the blood–brain barrier is restricted by tight junctions that connect endothelial cells of cerebral microvessels to one another in the brain parenchyma, as well as by protein transporters. Antimicrobial agents that are polar at physiological pH, such as penicillin G, generally penetrate poorly. Some drugs, such as penicillin G, are actively transported out of the cerebrospinal fluid. However, the integrity of the blood–brain barrier is diminished during active bacterial infection, such as pneumococcal meningitis, leading to an opening of the tight ...

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