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INTRODUCTION

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Overview

Most parasitic infections can be treated. Generally, drugs are effective against either protozoa or helminths, but not both. Some are well tolerated, while others are toxic or unpleasant for the patient. Antiparasitic resistance is a much more important issue in protozoan infections than helminth infections due to their more complex and slow life cycles. All providers should be familiar with the medications covered here.

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Parasites have been with us throughout human history, and the use of natural remedies to treat these infections date to ancient times. Indigenous people of the Amazon first used quinine-containing extracts of cinchona tree bark to treat malarious patients hundreds of years ago. In China, a recipe for malaria treatment using Qinghaosu tea was recorded by Ge Hong centuries earlier. Based on what we now know about the chemistry of these natural products, both remedies had a firm biochemical basis for their effectiveness. European investigators worked on creating new (and often highly toxic) treatments in the second half of the 19th century. By 1930, chemically synthesized drugs had been marketed for the treatment of malaria, trypanosomiasis, and schistosomiasis.

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Antiparasitic agents among first antimicrobials

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In spite of the introduction and explosive increase in the number and variety of antibacterials, antiparasitic medications have lagged far behind. Most antibacterials are ineffective against parasites, which share eukaryotic characteristics of their hosts. Because of the lack of safer alternatives, chemotherapeutics synthesized in the preantibiotic era remained critical elements of the parasitologist’s therapeutic armamentarium until very recently. Most required prolonged or parenteral administration. Their effectiveness was often restricted to particular disease stages, and their toxicity sometimes mandated that use be limited to very severe or life-threatening conditions. In time, newer antiparasitics were developed that overcame many of these problems. Their numbers are still limited, and only recently have their safety and efficacy begun to match those of their antibacterial equivalents.

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Newer antiparasitics have broader spectrum and are less toxic

Extreme need currently for more drugs

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Antiparasitic drug use and development has been shaped to a significant degree by the concentration of parasitic diseases in impoverished areas of the world. Community-based public health measures aimed at interrupting pathogen transmission—such as provision of sanitary facilities, clean water supplies, and insecticide-treated bed nets—are often beyond the means of tightly constrained local budgets. Consequently, the major burden of mitigating the impact of parasitic illnesses in endemic areas often falls on clinical officers or community health workers who, operating in remote and relatively under-resourced conditions, must examine, diagnose, and treat sick patients with whom they have only fleeting contact. Given these realities, optimal therapy for parasitic infections requires drugs that are effective in a single dose, easily administered, safe enough to be dispensed with limited medical supervision, sufficiently inexpensive to be widely used, and at low risk of accelerating drug resistance. Few such agents exist. Pharmaceutical companies, faced with the enormous costs ...

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