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Chapter 53: Clinical Pharmacology of the Antihelminthic Drugs

A missionary from the United States is sent to work in a geographic region of a Central American country where Onchocerca volvulus is endemic. Infections resulting from this tissue nematode (onchocerciasis) are a cause of “river blindness,” because microfilariae migrate through subcutaneous tissues and concentrate in the eyes. Which drug should be used prophylactically to prevent onchocerciasis?

(A) Albendazole

(B) Diethylcarbamazine

(C) Ivermectin

(D) Oxamniquine

(E) Pyrantel pamoate

Ivermectin prevents onchocerciasis and is the drug of choice in the individual and mass treatment of the disease. The only other drug listed with any activity against Onchocerca volvulus is diethylcarbamazine. Suramin (not listed) also has activity against onchocerciasis, but like diethylcarbamazine, it is less effective and more toxic than ivermectin. The answer is C.

A nonindigenous person who develops onchocerciasis in an endemic region and receives drug treatment is likely to experience a severe reaction. Symptoms include headache, weakness, rash, muscle aches, hypotension, and peripheral edema. Which statement concerning this reaction is accurate?

(A) Extensive fluid replacement is essential

(B) Symptoms are more intense in indigenous adults than nonindigenous adults

(C) The reaction is due to treatment with suramin

(D) The reaction is due to killing of microfilariae

(E) The symptoms are characteristic of treatment with diethylcarbamazine

The symptoms described are those of the so-called Mazzotti reaction. They are due to the killing by ivermectin of microfilariae, and their intensity correlates with skin microfilaria load and is not a drug toxicity. The reaction occurs more frequently and with greater severity in nonindigenous persons than in the indigenous inhabitants of endemic areas. The answer is D.

Which statement about pyrantel pamoate is accurate?

(A) Acts as an antagonist at GABA receptors

(B) Equivalent in efficacy to niclosamide in the treatment of tapeworm infections

(C) Eradicates adult worms in the colon but not the eggs

(D) Hepatotoxicity is dose-limiting

(E) Synergistic with praziquantel in cestode infections

Pyrantel pamoate, an agonist at nicotinic receptors, is equivalent to albendazole and mebendazole in the treatment of common nematode infections. It acts on adult worms in the colon, but not on eggs. The drug ...

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