A parasite is an organism that lives in or on another organism (the host) without contributing to the survival or well-being of the host. Helminthiasis (invasion of the body by helminths [worms]), malaria (an infectious disease caused by a protozoan and transmitted to humans through a bite from an infected mosquito), and amebiasis (invasion of the body by the ameba Entamoeba histolytica) are worldwide health problems caused by parasites.Pinworm is a helminth infection that is universally common; most other helminth infections are predominantly found in countries or areas of the world that lack proper sanitary facilities. Malaria is rare in the United States, but it is sometimes seen in individuals who have traveled to or lived in areas where this disease is a health problem. The first antimalarial drug, quinine, is derived from the bark of the cinchona tree. Amebiasis is seen throughout the world, but it is less common in developed countries where sanitary facilities prevent the spread of the causative organism.
ANTHELMINTIC DRUGS
Anthelmintic (against helminths) drugs are used to treat helminthiasis. Roundworms, pinworms, whipworms,hookworms, and tapeworms are examples of helminths.
ACTION, USES, AND ADVERSE
REACTIONS
Although the actions of anthelmintic drugs vary, their prime purpose is to kill the parasite. Adverse reactions associated with the anthelmintic drugs, if they do occur, are usually mild when the drug is used in the recom-mended dosage.
Albendazole
Albendazole (Albenza) interferes with the synthesis of the parasite’s microtubules, resulting in death of sus-ceptible larva. This drug is used to treat larval forms of pork tapeworm and to treat liver, lung, and peritoneum disease caused by the dog tapeworm.
Mebendazole
Mebendazole (Vermox) blocks the uptake of glucose by the helminth, resulting in a depletion of the helminth’s own glycogen. Glycogen depletion results in a decreased formation of adenosine triphosphate, which is required by the helminth for reproduction and survival. This drug is used to treat whipworm, pinworm, roundworm,American hookworm, and the common hookworm.Treatment with mebendazole may cause transient abdominal pain and diarrhea.
Pyrantel
The activity of pyrantel (Antiminth) is probably due to its ability to paralyze the helminth. Paralysis causes the helminth to release its grip on the intestinal wall; it is then excreted in the feces. Pyrantel is used to treat round-worm and pinworm. Some patients receiving pyrantel may experience gastrointestinal side effects, such as nau-sea, vomiting, abdominal cramps, or diarrhea.
Thiabendazole
The exact mechanism of action of thiabendazole (Mintezol) is unknown. This drug appears to suppress egg or larval production and therefore may interrupt the life cycle of the helminth. Thiabendazole is used to treat threadworm. Thiabendazole may cause hypersensitivity reactions, drowsiness, and dizziness.
CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS
Albendazole
Albendazole is contraindicated in patients with known hypersensitivity to the drug and during pregnancy (Category C). The drug has exhibited embryotoxic and teratogenic effects in experimental animals. Albendazole is used cautiously in patients with hepatic impairment and during lactation. The effects of albendazole are increased with dexamethasone and cimetidine.
Mebendazole
Mebendazole is contraindicated in patients with known hypersensitivity. Mebendazole is also contraindicated during pregnancy (Category C). The drug, like albenda-
zole, has exhibited embryotoxic and teratogenic effects in experimental animals. Administration of mebenda-zole with the hydantoins and carbamazepine may
reduce plasma levels of mebendazole.
Pyrantel
Pyrantel is contraindicated in patients with known hypersensitivity. Pyrantel is used with caution in indi-viduals with liver dysfunction, malnutrition, or anemia. Pyrantel is a Pregnancy Category C drug and is used during pregnancy only if the potential benefit out-weighs the risk to the fetus. Pyrantel and piperazine are
antagonists and should not be given together.
Thiabendazole
Thiabendazole is contraindicated in patients with known hypersensitivity. Thiabendazole is used with caution in patients with hepatic or renal disease.
Thiabendazole is a Pregnancy Category C drug and is used during pregnancy only if the potential benefit out-weighs the risk to the fetus. When thiabendazole is administered with the xanthine derivatives, the plasma level of the xanthine may increase to toxic levels. It is important to monitor xanthine plasma levels closely in case a dosage reduction is necessary.
ANTIMALARIAL DRUGS
Malaria is transmitted from person to person by a cer tain species of the Anopheles mosquito. The four differ ent protozoans causing malaria are Plasmodium falci parum, P. malariae, P. ovale, and P. vivax. Drugs used to treat or prevent malaria are called antimalarial drugs Three antimalarial drugs arechloroquine, doxycycline, and quinine sulfate.
ACTIONS
The plasmodium causing malaria must enter the mos-quito to develop, reproduce, and be transmitted. When the mosquito bites a person infected with malaria, it ingests the male and female forms (gametocytes) of the plasmodium. The gametocytes mate in the mosquito’s stomach and ultimately form sporozoites (an animalreproductive cell) that make their way to the salivary glands of the mosquito. When the mosquito bites a noninfected person, the sporozoites enter the person’s bloodstream and lodge in the liver and other tissues.The sporozoites then undergo asexual cell division and reproduction and form merozoites (cells formed as a result of asexual reproduction). The merozoites then divide asexually and enter the red blood cells of the person, where they form the male and female forms of the plasmodium. The symptoms of malaria (shaking, chills,and fever) appear when the merozoites enter the indi
vidual’s red blood cells.Antimalarial drugs interfere with, or are active against, the life cycle of the plasmodium, primarily when it is present in the red blood cells. Destruction at this stage of the plasmodium life cycle prevents the development of the male and female forms of the plas-modium. This in turn keeps the mosquito (when the mosquito bites an infected individual) from ingesting the male and female forms of the plasmodium, thus effectively ending the plasmodium life cycle
USES
Two terms are used when discussing the uses of antimalarial drugs:
1. Suppression—the prevention of malaria
2. Treatment—the management of a malarial attack
Not all antimalarial drugs are effective in suppressing or treating all four of the Plasmodium species that cause malaria. In addition, resistant strains have developed,and some antimalarial drugs are no longer effective against some of these strains. The primary health care provider must select the antimalarial drug that reportedly is effective, at present, for the type of malaria the individual either has (treatment) or could be exposed to (prevention) in a specific area of the world.Chloroquine (Aralen) is also used in the treatment of extraintestinal amebiasis (see section on Amebicides).Doxycycline is also used to treat infections caused by Neisseria gonorrhoeae, Treponema pallidum, Listeria mono-cytogenes, Clostridium, and Bacillus anthracis when peni-cillin is contraindicated. Quinine also may be used for the prevention and treatment of nocturnal leg cramps.
ADVERSE REACTIONS
Chloroquine
The adverse reactions associated with the administra-tion of chloroquine (Aralen HCl and phosphate) and hydroxychloroquine include hypotension, electrocardiographic changes, visual disturbances, headache, nausea,vomiting, anorexia, diarrhea, and abdominal cramps.
Doxycycline
Doxycycline (Vibramycin) is an antibiotic belonging to the tetracycline group of antibiotics. and include photosensitivity, anorexia, nausea, and vomiting.
Quinine
The use of quinine can cause cinchonism at full thera-peutic doses. Cinchonism is a group of symptoms asso-ciated with quinine, including tinnitus, dizziness, headache, gastrointestinal disturbances, and visual dis-turbances. These symptoms usually disappear when the dosage is reduced. Other adverse reactions include hematologic changes, vertigo, and skin rash.
CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS
Chloroquine
Chloroquine is contraindicated in patients with known hypersensitivity. It is a good idea to use chloroquine cautiously in patients with hepatic disease or bone marrow depression and during pregnancy. Children are very sensitive to chloroquine, and the drug should be used with extreme caution in children.Because the effects of chloroquine during pregnancy (Pregnancy Category C) are unknown, this drug is given only when clearly needed and the potential benefits outweigh potential hazards to the fetus. There is an increased risk of hepatotoxicity when chloroquine is administered with other hepatotoxic drugs.Foods that acidify the urine (cranberries, plums,prunes, meats, cheeses, eggs, fish, and grains) may increase excretion and decrease the effectiveness of chloroquine.
Doxycycline
Doxycycline is contraindicated in patients with known hypersensitivity. Because the effects of doxycycline dur-ing pregnancy (Category D) are unknown, this drug is contraindicated during pregnancy. The drug is used cautiously in patients with renal or hepatic impairment and during lactation. There is a decreased absorption of the drug when administered with antacids or iron. There is a decrease of the therapeutic effects of doxycycline when the drug is administered with barbiturates,phenytoins, and carbamazepine. There is an increased risk of digoxin toxicity when digoxin is administered with doxycycline.
Quinine
Quinine is contraindicated in patients with known hyper-sensitivity. The drug is also contraindicated in pregnant women (Pregnancy Category X) and in patients with myasthenia gravis (may cause respiratory distress and dysphagia). Quinine absorption is delayed when adminis-tered with antacids containing aluminum. Plasma digitalis levels may increase when digitalis preparations and qui-nine are given concurrently. Plasma levels of warfarin are increased when administered with quinine.
AMEBICIDES
Amebicides (drugs that kill amebas) are used to treat amebiasis caused by the parasite E. histolytica. An ameba is a one-celled organism found in soil and water
ACTIONS AND USES
These drugs are amebicidal (ie, they kill amebas). There are two types of amebiasis: intestinal and extraintestinal.In the intestinal form, the ameba is confined to the intes-tine. In the extraintestinal form, the ameba is found outside of the intestine, such as in the liver. The extrain-testinal form of amebiasis is more difficult to treat.Iodoquinol (Yodoxin) and metronidazole (Flagyl) areused to treat intestinal amebiasis. Metronidazole is also used to treat infections caused by susceptible microorganismsan aminoglycoside with amebicidal activity and is used to treat intestinal amebiasis. Chloroquine hydrochloride (Aralen) is used to treat extraintestinal amebiasis.
ADVERSE REACTIONS
Chloroquine
Hypotension, electrocardiographic changes, headache,nausea, vomiting, anorexia, diarrhea, abdominal cramps,and psychic stimulation can occur with the use of chloroquine hydrochloride or phosphate.
Iodoquinol
Various types of skin eruptions, nausea, vomiting, fever,chills, abdominal cramps, vertigo, and diarrhea can occurwith administration of iodoquinol.
Metronidazole
Convulsive seizures, headache, nausea, and periphera neuropathy (numbness and tingling of the extremities)have been reported with the use of metronidazole.
Paromomycin
This drug has relatively few adverse reactions. The most common include nausea, vomiting, and diarrhea The more serious adverse reactions, although rare, are
nephrotoxicity and ototoxicity.
CONTRAINDICATIONS,
PRECAUTIONS, AND INTERACTIONS
Chloroquine
Chloroquine is contraindicated in patients with known hypersensitivity.
Iodoquinol
Iodoquinol is contraindicated in patients with known hypersensitivity. Iodoquinol is used with caution in patients with thyroid disease and during pregnancy and lactation. Iodoquinol may interfere with the results of thyroid function tests. This interference not only occurs during therapy, but may last as long as 6 months after
iodoquinol therapy is discontinued.
Metronidazole
Metronidazole is contraindicated in patients with known hypersensitivity. Metronidazole is contraindicated during the first trimester of pregnancy (Category B). Metronidazole is given during the second and third trimesters of pregnancy. Metronidazole is used cautiously in patients with blood dyscrasias, seizure disorders, and severe hepatic impairment. The patient must avoid alcohol while taking metronidazole.When metronidazole is administered with cimetidine, the metabolism of metronidazole is decreased;
when it is administered with phenobarbital, the metabolism is increased, possibly causing a decrease in the
effectiveness of metronidazole. Metronidazole increases the effects of warfarin.Paromomycin
Paromomycin is contraindicated in patients with knownhypersensitivity. Paromomycin is given with caution during pregnancy. Paromomycin is used with caution in patients with bowel disease. High doses and prolonged therapy are avoided because the drug may be absorbed in large amounts by patients with bowel disease, causing ototoxicity and renal impairment.
ANTHELMINTIC DRUGS
Anthelmintic (against helminths) drugs are used to treat helminthiasis. Roundworms, pinworms, whipworms,hookworms, and tapeworms are examples of helminths.
ACTION, USES, AND ADVERSE
REACTIONS
Although the actions of anthelmintic drugs vary, their prime purpose is to kill the parasite. Adverse reactions associated with the anthelmintic drugs, if they do occur, are usually mild when the drug is used in the recom-mended dosage.
Albendazole
Albendazole (Albenza) interferes with the synthesis of the parasite’s microtubules, resulting in death of sus-ceptible larva. This drug is used to treat larval forms of pork tapeworm and to treat liver, lung, and peritoneum disease caused by the dog tapeworm.
Mebendazole
Mebendazole (Vermox) blocks the uptake of glucose by the helminth, resulting in a depletion of the helminth’s own glycogen. Glycogen depletion results in a decreased formation of adenosine triphosphate, which is required by the helminth for reproduction and survival. This drug is used to treat whipworm, pinworm, roundworm,American hookworm, and the common hookworm.Treatment with mebendazole may cause transient abdominal pain and diarrhea.
Pyrantel
The activity of pyrantel (Antiminth) is probably due to its ability to paralyze the helminth. Paralysis causes the helminth to release its grip on the intestinal wall; it is then excreted in the feces. Pyrantel is used to treat round-worm and pinworm. Some patients receiving pyrantel may experience gastrointestinal side effects, such as nau-sea, vomiting, abdominal cramps, or diarrhea.
Thiabendazole
The exact mechanism of action of thiabendazole (Mintezol) is unknown. This drug appears to suppress egg or larval production and therefore may interrupt the life cycle of the helminth. Thiabendazole is used to treat threadworm. Thiabendazole may cause hypersensitivity reactions, drowsiness, and dizziness.
CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS
Albendazole
Albendazole is contraindicated in patients with known hypersensitivity to the drug and during pregnancy (Category C). The drug has exhibited embryotoxic and teratogenic effects in experimental animals. Albendazole is used cautiously in patients with hepatic impairment and during lactation. The effects of albendazole are increased with dexamethasone and cimetidine.
Mebendazole
Mebendazole is contraindicated in patients with known hypersensitivity. Mebendazole is also contraindicated during pregnancy (Category C). The drug, like albenda-
zole, has exhibited embryotoxic and teratogenic effects in experimental animals. Administration of mebenda-zole with the hydantoins and carbamazepine may
reduce plasma levels of mebendazole.
Pyrantel
Pyrantel is contraindicated in patients with known hypersensitivity. Pyrantel is used with caution in indi-viduals with liver dysfunction, malnutrition, or anemia. Pyrantel is a Pregnancy Category C drug and is used during pregnancy only if the potential benefit out-weighs the risk to the fetus. Pyrantel and piperazine are
antagonists and should not be given together.
Thiabendazole
Thiabendazole is contraindicated in patients with known hypersensitivity. Thiabendazole is used with caution in patients with hepatic or renal disease.
Thiabendazole is a Pregnancy Category C drug and is used during pregnancy only if the potential benefit out-weighs the risk to the fetus. When thiabendazole is administered with the xanthine derivatives, the plasma level of the xanthine may increase to toxic levels. It is important to monitor xanthine plasma levels closely in case a dosage reduction is necessary.
ANTIMALARIAL DRUGS
Malaria is transmitted from person to person by a cer tain species of the Anopheles mosquito. The four differ ent protozoans causing malaria are Plasmodium falci parum, P. malariae, P. ovale, and P. vivax. Drugs used to treat or prevent malaria are called antimalarial drugs Three antimalarial drugs arechloroquine, doxycycline, and quinine sulfate.
ACTIONS
The plasmodium causing malaria must enter the mos-quito to develop, reproduce, and be transmitted. When the mosquito bites a person infected with malaria, it ingests the male and female forms (gametocytes) of the plasmodium. The gametocytes mate in the mosquito’s stomach and ultimately form sporozoites (an animalreproductive cell) that make their way to the salivary glands of the mosquito. When the mosquito bites a noninfected person, the sporozoites enter the person’s bloodstream and lodge in the liver and other tissues.The sporozoites then undergo asexual cell division and reproduction and form merozoites (cells formed as a result of asexual reproduction). The merozoites then divide asexually and enter the red blood cells of the person, where they form the male and female forms of the plasmodium. The symptoms of malaria (shaking, chills,and fever) appear when the merozoites enter the indi
vidual’s red blood cells.Antimalarial drugs interfere with, or are active against, the life cycle of the plasmodium, primarily when it is present in the red blood cells. Destruction at this stage of the plasmodium life cycle prevents the development of the male and female forms of the plas-modium. This in turn keeps the mosquito (when the mosquito bites an infected individual) from ingesting the male and female forms of the plasmodium, thus effectively ending the plasmodium life cycleUSES
Two terms are used when discussing the uses of antimalarial drugs:
1. Suppression—the prevention of malaria
2. Treatment—the management of a malarial attack
Not all antimalarial drugs are effective in suppressing or treating all four of the Plasmodium species that cause malaria. In addition, resistant strains have developed,and some antimalarial drugs are no longer effective against some of these strains. The primary health care provider must select the antimalarial drug that reportedly is effective, at present, for the type of malaria the individual either has (treatment) or could be exposed to (prevention) in a specific area of the world.Chloroquine (Aralen) is also used in the treatment of extraintestinal amebiasis (see section on Amebicides).Doxycycline is also used to treat infections caused by Neisseria gonorrhoeae, Treponema pallidum, Listeria mono-cytogenes, Clostridium, and Bacillus anthracis when peni-cillin is contraindicated. Quinine also may be used for the prevention and treatment of nocturnal leg cramps.
ADVERSE REACTIONS
Chloroquine
The adverse reactions associated with the administra-tion of chloroquine (Aralen HCl and phosphate) and hydroxychloroquine include hypotension, electrocardiographic changes, visual disturbances, headache, nausea,vomiting, anorexia, diarrhea, and abdominal cramps.
Doxycycline
Doxycycline (Vibramycin) is an antibiotic belonging to the tetracycline group of antibiotics. and include photosensitivity, anorexia, nausea, and vomiting.
Quinine
The use of quinine can cause cinchonism at full thera-peutic doses. Cinchonism is a group of symptoms asso-ciated with quinine, including tinnitus, dizziness, headache, gastrointestinal disturbances, and visual dis-turbances. These symptoms usually disappear when the dosage is reduced. Other adverse reactions include hematologic changes, vertigo, and skin rash.
CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS
Chloroquine
Chloroquine is contraindicated in patients with known hypersensitivity. It is a good idea to use chloroquine cautiously in patients with hepatic disease or bone marrow depression and during pregnancy. Children are very sensitive to chloroquine, and the drug should be used with extreme caution in children.Because the effects of chloroquine during pregnancy (Pregnancy Category C) are unknown, this drug is given only when clearly needed and the potential benefits outweigh potential hazards to the fetus. There is an increased risk of hepatotoxicity when chloroquine is administered with other hepatotoxic drugs.Foods that acidify the urine (cranberries, plums,prunes, meats, cheeses, eggs, fish, and grains) may increase excretion and decrease the effectiveness of chloroquine.
Doxycycline
Doxycycline is contraindicated in patients with known hypersensitivity. Because the effects of doxycycline dur-ing pregnancy (Category D) are unknown, this drug is contraindicated during pregnancy. The drug is used cautiously in patients with renal or hepatic impairment and during lactation. There is a decreased absorption of the drug when administered with antacids or iron. There is a decrease of the therapeutic effects of doxycycline when the drug is administered with barbiturates,phenytoins, and carbamazepine. There is an increased risk of digoxin toxicity when digoxin is administered with doxycycline.
Quinine
Quinine is contraindicated in patients with known hyper-sensitivity. The drug is also contraindicated in pregnant women (Pregnancy Category X) and in patients with myasthenia gravis (may cause respiratory distress and dysphagia). Quinine absorption is delayed when adminis-tered with antacids containing aluminum. Plasma digitalis levels may increase when digitalis preparations and qui-nine are given concurrently. Plasma levels of warfarin are increased when administered with quinine.
AMEBICIDES
Amebicides (drugs that kill amebas) are used to treat amebiasis caused by the parasite E. histolytica. An ameba is a one-celled organism found in soil and water
ACTIONS AND USES
These drugs are amebicidal (ie, they kill amebas). There are two types of amebiasis: intestinal and extraintestinal.In the intestinal form, the ameba is confined to the intes-tine. In the extraintestinal form, the ameba is found outside of the intestine, such as in the liver. The extrain-testinal form of amebiasis is more difficult to treat.Iodoquinol (Yodoxin) and metronidazole (Flagyl) areused to treat intestinal amebiasis. Metronidazole is also used to treat infections caused by susceptible microorganismsan aminoglycoside with amebicidal activity and is used to treat intestinal amebiasis. Chloroquine hydrochloride (Aralen) is used to treat extraintestinal amebiasis.
ADVERSE REACTIONS
Chloroquine
Hypotension, electrocardiographic changes, headache,nausea, vomiting, anorexia, diarrhea, abdominal cramps,and psychic stimulation can occur with the use of chloroquine hydrochloride or phosphate.
Iodoquinol
Various types of skin eruptions, nausea, vomiting, fever,chills, abdominal cramps, vertigo, and diarrhea can occurwith administration of iodoquinol.
Metronidazole
Convulsive seizures, headache, nausea, and periphera neuropathy (numbness and tingling of the extremities)have been reported with the use of metronidazole.
Paromomycin
This drug has relatively few adverse reactions. The most common include nausea, vomiting, and diarrhea The more serious adverse reactions, although rare, are
nephrotoxicity and ototoxicity.
CONTRAINDICATIONS,
PRECAUTIONS, AND INTERACTIONS
Chloroquine
Chloroquine is contraindicated in patients with known hypersensitivity.
Iodoquinol
Iodoquinol is contraindicated in patients with known hypersensitivity. Iodoquinol is used with caution in patients with thyroid disease and during pregnancy and lactation. Iodoquinol may interfere with the results of thyroid function tests. This interference not only occurs during therapy, but may last as long as 6 months after
iodoquinol therapy is discontinued.
Metronidazole
Metronidazole is contraindicated in patients with known hypersensitivity. Metronidazole is contraindicated during the first trimester of pregnancy (Category B). Metronidazole is given during the second and third trimesters of pregnancy. Metronidazole is used cautiously in patients with blood dyscrasias, seizure disorders, and severe hepatic impairment. The patient must avoid alcohol while taking metronidazole.When metronidazole is administered with cimetidine, the metabolism of metronidazole is decreased;
when it is administered with phenobarbital, the metabolism is increased, possibly causing a decrease in the
effectiveness of metronidazole. Metronidazole increases the effects of warfarin.Paromomycin
Paromomycin is contraindicated in patients with knownhypersensitivity. Paromomycin is given with caution during pregnancy. Paromomycin is used with caution in patients with bowel disease. High doses and prolonged therapy are avoided because the drug may be absorbed in large amounts by patients with bowel disease, causing ototoxicity and renal impairment.
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