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INTRODUCTION

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 the worms’ more complex and slow life cycles. All providers should be familiar with the medications covered here.

Parasites have been with us throughout human history, and the use of natural remedies to treat these infections date to antiquity. Quinine-containing extracts of cinchona tree bark were used to treat malaria 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. By 1930, chemically synthesized drugs had been marketed for the treatment of malaria, trypanosomiasis, and schistosomiasis.

Antiparasitic agents among first antimicrobials

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. Most antiparasitics were only partially effective, toxic, and required prolonged or parenteral administration. 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.

Newer antiparasitics broader spectrum, less toxic

Antiparasitic drug use and development have 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 under-resourced conditions, must examine, diagnose, and treat sick patients with whom they may have only fleeting contact. Given these realities, optimal therapy for parasitic infections requires drugs that are effective in a single oral 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 of drug development and approval, have been reluctant to expend capital they are unlikely to recover. Public–private partnerships, cofinanced and operated by philanthropic organizations, industry, and academia, provide an exciting model that may yield the next wave of effective treatment for parasitic infections.

Treatment programs difficult in emerging economies

STRUCTURE AND ACTION

With few exceptions, antiparasitic agents have been synthesized de novo rather ...

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