Blood schizonticides

Agents such as quinine, quinacrine, amodiaquine, and chloroquine suppress the symptoms of malaria by destroying the schizonts and merozoites in the erythrocytes. 

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Blood Schizonticides. These destroy the erythrocytic stages of the parasites and are useful for the clinical cure of falcipamm malaria or suppression of relapsing infections. 

The dmgs known as antifolates act as effective blood schizonticides. Unfortunately, the parasites readily develop resistance to them. Most antifolates show poor oral tolerance, absorption, and host toxicity. They fall into two types depending on the mechanisms by which they operate. 

Antimalarial therapy employs the same agents and is based on the same principles. The blood-schizonticidal halofantrine is reserved for therapy only. The pyrimethamine-sulfadoxine combination may be used for initial selftreatment. 

Mefloquine is also a 4-aminoquinoline. It is a blood schizonticide active against the asexual stages of all malaria parasites. Mefloquine is currently the prophylactic agent of choice for short-term travellers. Resistance of P. falciparum against mefloquine has occurred in South-East Asia. Only an oral... 

VI.a.2.2. Biguanides. Proguanil is a dihydrofolate reductase inhibitor. It is a slow acting blood schizonticide and not effective on its own. It has also a marked effect on the primary tissue stages of Plasmodium falciparum. It is used in combination with chloroquine for the prophylaxis of chloroquine-resistant Plasmodium falciparum. 

Quinine is the principal alkaloid derived from the bark of the cinchona tree. It has been used for malaria suppression for over 300 years. By 1959 it was superseded by other drugs, especially chloroquine. After widespread resistance to chloroquine became manifest quinine again became an important antimalarial. Its main uses are for the oral treatment of chloroquine-resistant falciparum malaria and for parenteral treatment of severe attacks of falciparum malaria. Quinine is a blood schizonticide with some gametocytocidal activity. It has no exoerythrocytic activity. Its mechanism of action is not well understood. It can interact with DNA, inhibiting strand separation and ultimately protein synthesis. Resistance of quinine has been increasing in South-East Asia. 

Halofantrine, a 9-phenanthrenemethanol derivative, is a blood schizonticide and is active against Plasmodium vivax and chloroquine sensitive as well as chloroquine resistant strains of Plasmodium falciparum. As no parenteral preparation is available it cannot be used for severely ill patients. Oral absorption is slow and incomplete and is increased by a fatty meal. 

Quinacrine, a 9-aminoacridine, is a blood schizonticide with activity against all four types of... 

While its detailed mechanism of action is unknown, it is an effective blood schizonticide that is, it acts against the form of the parasite responsible for chnical symptoms. Orally administered mefloquine is well absorbed and has an absorption half-hfe of about 2 hours the elimination half-hfe is 2 to 3 weeks. Among its side effects are vertigo, visual alterations, vomiting, and such CNS disturbances as psychosis, hallucinations, confusion, anxiety, and depression. It should not be used concurrently with compounds known to alter cardiac conduction or prophylactically in patients operating dangerous machinery. It should not used to treat severe malaria, as there is no intravenous formulation. 

Life cycle of malaria parasites. Only the asexual erythrocytic stage of infection causes clinical malaria. All effective antimalarial treatments are blood schizonticides that kill this stage. 

When not limited by resistance, chloroquine is a highly effective blood schizonticide. It is also moderately effective against gametocytes of P vivax, P ovale, and P malariae but not against those of P falciparum. Chloroquine is not active against liver stage parasites. 

Mefloquine has strong blood schizonticidal activity against P falciparum and P vivax, but it is not active against hepatic sta-ges or gametocytes. The mechanism of action of mefloquine is unknown. 

Answer No. This drug is a blood schizonticide and acts as a malarial suppressant for P. vivax. 

The recently introduced antimalanal halofantrine (6) is an orally active blood schizonticide reported to be more than 95% effective in the treatment of malaria [S] Mefloquine hydrochloride (7) contmues to be useful m the prophylaxis and treatment of malana [9]... 

Piperaquine is a sjmthetic 4-aminoquinoline with high blood schizonticidal activity, similar to that of chloro-quine (SEDA-13, 810). There is some evidence that piperaquine is active against chloroquine-resistant Plasmodium falciparum, but laboratory studies suggest a degree of cross-resistance. Piperaquine 600 mg/month... 

Drugs used to treat an acute attack. Blood schizonticides are used to suppress an acute attack, and the various drugs used include oral chloroquine, mefloquine or quinine plus pyrimethamine or doxycycline or halofantrine. 

The ethanolic extract of the fruit showed significant blood schizonticidal activity in Plasmodium berghei infected mice and anti inflammatory activity 114, 115). Nwiawu et al. 116) have reported on the anticonvulsant properties of the essential oil of the fruit. 

Chinese herbal medicine may have made a contribution to the treatment of malaria. The herb Quinghao (Artemisia annua), in use over a millennium, has finally yielded its active principle quinghaosu or artemisinine (Fig. 7-6), a sesquiterpene lactone containing a peroxide bridge. Clinical evaluation of it and several derivatives in the late 1970s was reported to have achieved successful treatment in over 2,000 patients, many with chloroquine-resis-tant falciparum. Their activity is blood schizonticidal. The mechanism does not appear to be antifolate or intercalation. The peroxide is essential, which raises a suspicion of free radical damage to the parasite. 

Mefloquine is an antimalarial preparation that acts as a blood schizonticide. It is indicated in the treatment of mild to moderate malaria caused by mefloquine-susceptible strains of Plasmodium falciparum or P. vivax and prevention of malaria caused by P. falciparum or P. vivax. Patients with acute P. vivax need subsequent treatment with 9-ami-noquinolone to prevent relapse. 

Pyrimethamine is a folic-acid antagonist its therapeutic action is based on differential requirements between host and parasite for nucleic acid precursors involved in growth as it selectively inhibits plasmodial dihydrofolate reductase. Pyrimethamine inhibits the enzyme dihydrofolate reductase that catalyzes the reduction of dihydrofolate to tetrahydro-folate. This activity is highly selective against plasmodia and Toxoplasma gondii. It does not destroy gametocytes but arrests sporogony in the mosquito. Pyrimethamine possesses a blood schizonticidal, and some tissue schizonticidal activity may be slower than that of 4-amino-quinoline compounds. 

Quinine, a cinchona alkaloid, acts primarily as a blood schizonticide. Qninine s antimalarial action is unclear. It was once believed to be dne to the intercalation of the qninoline moiety into the DNA of the parasite, thereby reducing the effectiveness of DNA to act as a template, as well as depression of the oxygen uptake and carbohydrate metabolism of the plasmodia. Recently it has been thonght that quinine s pH elevation in the intracellular organelles of the parasites plays a role in the mechanism. 

Artemisinin (qinghaosu) provides a more recent example of a plant-derived antimalarial agent. Based on the reputed antimalarial use of Artemisia annua in the Chinese system of traditional medicine, artemisinin was isolated from the plant as the active compound, developed as a drug, and released for clinical use as a blood schizonticide (66-68). Artemisinin is a... 

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