Antimalaria drugs
Life cycleLife cycle of malaria
• Hepatic cycle• Erythrocyte cycle
• Sexual form
Hepatic cycle
Sporozoites enter liver cells where they develop into schizonts, which form large numbers of merozoites which are released into the circulationPrimaquine, proguanil, and tetracyclines act at this site and are used for:
Radical cure (an attack on persisting hepatic forms (hypnozoites, i.e sleeping)
Preventing the initial hepatic cycle primaquine
Erythrocyte cycle
Merozoites enter red cells, where they develop into schizonts, which form more merozoites that ate released when the cells burst, giving rise to the features of the clinical attack. The merozoites re-enter red cells and the cycle is repeated.Chloroquine, quinine, mefloquine, halfantrine, proguanil, pyrimethamine and tetracyclines.
Erythrocyte cycle
Drugs that act at this stage in the cycle of the parasite may be used for:
Treatment of acute attacks of malaria
Prevention of attacks by early destruction of the erythrocytic forms
Sexual forms
Some merozoites differentiate into male and female gametocytes in the erythrocytes and can develop further only if they are ingested by a mosquito where they form sporozoites and complete the transmission cycle.Quinine, mefloquine, chloroquine, and primaquine.
Anti malaria individual drugs
ChloroquineIs concentrated within parasitised red cells and forms complexes with plasmodial DNA.
It is active against the blood forms and also gametocytes of plasmodium vivax, plasmodium ovale, and plasmodium malarae
Is ineffective against many strains of plasmodium falciparum.
Chloroquine
Adverse effectsCorneal deposits of chloroquine may be asymptomatic or may cause halos around lights or photophobia (this is not threat the vision and reverse when the drug is stopped
Retinal toxicity is more serious and may be irreversible
Other reactions include pruritis, headaches, gastrointestinal disturbance.
Halofantrine
Is active against the erythrocytic form of all four plasmodium species, especially plasmodium falciparum and plasmodium vivax and at the schizont stage, its mechanism of action is not fully understood.
Halofantrine
Halofantrine may cause gastrointestinal symptoms, symptoms, pruritus occurs but to a lesser extent than chloroquineIt prolongs the cardiac QT interval and may predispose to hazardous arrhythmia.
Mefloquine
Is similar in several respects to quinine is used in chemoprophylaxis and occasionally to treat uncomplicated plasmodium falciparum and chloroquine-resistant plasmodium vivax malairaMefloquine
Adverse effectsInclude nausea, dizziness, disturbance of balance, vomiting, abdominal pain, hallucinations, seizures and psychoses occur.
Primaquine
Act at several stages in the development of the plasmodial parasite, possibly by interfering with its mitochondrial function. Its unique effect is to eliminate the hepatic forms after standard chloroquine therapyAdverse effects include anorexia, nausea, abdominal cramps, methemoglobinemia and hemolytic anemia.
Proguanil
Inhibits dihydrofolate reductase which converts folic to folinic acid, deficiency of which inhibits plasmodial cell division.Adverse effects in prophylactic doses proguanil is well tolerated. Mouth ulcers and stomatitis have been reported
Pyrimethamine
Inhibits plasmodial dihydrofolate reductase for which it has a high affinity.
Adverse effects reported include anorexia abdominal cramps, vomiting , ataxia, tremor, seizures and megalobastic anemia.
Pyrimethamine with slufadoxine
Is now used with quinine to treat acute attacks of malaria caused by susceptible strains of plasmodium falciparum.Quinine
Is obtained from the bark of the south American cinchona tree. It binds to plasmodial DNA to prevent protein synthesis but its exact mode action remains uncertain. It is used to treat plasmodium falciparum malaria in areas of multiple dug resistance.Quinine
Adverse effectsInclude tinnitus, diminished auditory acuity, headache, blurred vision, nausea and diarrhea
Idiosyncratic reactions include pruritis, urticaria and rashes.