Antiprotozoal and anthelminthic therapy

44. Antiprotozoal and anthelminthic therapy




Questions


image Why is the choice of antiparasitic drugs limited?

image Which is the drug of choice for Echinococcus cysts?

image Which antiparasitic drug has activity against Cryptosporidium parvum?

Recent years have seen many advances in parasitology, particularly antimalarial agents. However, the treatment of many infections remains unsatisfactory. Effective therapeutic agents are limited and of disappointing activity for several reasons:


image similarities between parasite and humans cells can result in drug side-effects

image drugs may not be active against all biological forms of an organism (cyst and eggs are particularly resistant)

image parasites may be in sites that are harder for drugs to access

image drug resistance has limited the effectiveness of many agents, particularly in malaria.


Antimalarial agents


The choice of the correct agent to treat malaria is essential and is based on clinical history, symptoms and examination of blood films (see Ch. 33).


Quinine, a quinolinemethanol of the bark of the chinchoa tree, is active against the erythrocytic stages of Plasmdium falciparum, but not its gametocytes. It causes cinchoism (tinnitus, nausea and headaches), hypoglycaemia and sometimes arrhythmias. It has become the first-line treatment for falciparum malaria, because resistance is very rare.


Artemisins are extracts of the qinghaosu plant and are available as intravenous artesunate, intramuscular artemether and as an oral combination with lumefantrin. It is active against all stages of all plasmodial species and reduces parasite counts rapidly. It is used for patients with falciparum malaria in whom quinine is contraindicated.


Chloroquine, a 4-aminoquinoline, is active against trophozoites and gametocytes of all plasmodial species, but not against schizonts and hypnozoites. Resistance has developed in many holoendemic countries. It has also activity against Entamoeba histolytica.


Mefloquine, a 4-quinolinemethanol, is active against the erythrocytic stages of all plasmodial species. It has also antibacterial and antifungal activity. Chloroquine-resistant strains remain sensitive, whereas there is cross-resistance with quinine. Psychotropic side-effects are reported in 1:1500 treatments. It is used for malaria prophylaxis and also for cutaneous leishmaniasis.


Primaquine, an 8-aminoquinolone, is active against the hepatic stages of P. vivax and P. ovale and against gametocytes. It induces haemolysis in those with glucose-6-phosphate dehydrogenase deficiency. It is used in combination with chloroquine for non-falciparum malaria.


Atovaquone, a hydroxynaphthoquinone, is active against all stages of P. falciparum, Toxoplasma gondii, Babesia sp. and Pneumocystis jirovecii. It is used as third-line treatment for P. jirovecii pneumonia (was known as P. carinii and hence the pneumonia is referred to as PCP) and in combination with proguanil for malaria prophylaxis.

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Antiprotozoal and anthelminthic therapy

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