Proguanil is a prophylactic antimalarial drug, which works by stopping the malaria parasite, Plasmodium falciparum and Plasmodium vivax, from reproducing once it is in the red blood cells. Proguanil in combination with atovaquone are marked under the brand name malarone, which is indicated for the treatment of acute, uncomplicated P. falciparum malaria and for the prophylaxis of Plasmodium falciparum malaria, including in areas where chloroquine resistance has been reported. Atovaquone and proguanil, interfere with 2 different pathways involved in the biosynthesis of pyrimidines required for nucleic acid replication. Atovaquone is a selective inhibitor of parasite mitochondrial electron transport. Proguanil hydrochloride primarily exerts its effect by means of the metabolite cycloguanil, a dihydrofolate reductase inhibitor. Inhibition of dihydrofolate reductase in the malaria parasite disrupts deoxythymidylate synthesis. Recently were done experiments, which confirmed the hypothesis that proguanil might act on another target than dihydrofolate reductase. In addition, was made conclusion, that effectiveness of malarone was due to the synergism between atovaquone and proguanil and may not require the presence of cycloguanil.

Atovaquone is a chemical compound that belongs to the class of naphthoquinones; it is manufactured in the US in the liquid form, or oral suspension, under the brand name Mepron. Meron is used for the treatment or prevention of Pneumocystis carinii pneumonia in patients who are intolerant to trimethoprim-sulfamethoxazole (TMP-SMX). Also indicated for the acute oral treatment of mild to moderate PCP in patients who are intolerant to TMP-SMX. The mechanism of action against Pneumocystis jiroveci has not been fully elucidated. In Plasmodium species, the site of action appears to be the cytochrome bc1 complex (Complex III). Several metabolic enzymes are linked to the mitochondrial electron transport chain via ubiquinone. Inhibition of electron transport by atovaquone results in indirect inhibition of these enzymes. The ultimate metabolic effects of such blockade may include inhibition of nucleic acid and adenosine triphosphate (ATP) synthesis. Several laboratories, using different in vitro methodologies, have shown the IC50 (50% inhibitory concentration) of atovaquone against P. jiroveci to be 0.1 to 3.0 mcg/mL.

Primaquine is a oral medication used to treat and prevent malaria and to treat Pneumocystis pneumonia. Specifically it is used for malaria due to Plasmodium vivax and Plasmodium ovale along with other medications and for prevention if other options cannot be used. Primaquine is an alternative treatment for Pneumocystis pneumonia together with clindamycin. Primaquine is lethal to P. vivax and P. ovale in the liver stage, and also to P. vivax in the blood stage through its ability to do oxidative damage to the cell. However, the exact mechanism of action is not fully understood. Primaquine is well-absorbed in the gut and extensively distributed in the body without accumulating in red blood cells. Administration of primaquine with food or grapefruit juice increases its oral bioavailibity. In blood, about 20% of circulating primaquine is protein-bound, with preferential binding to the acute phase protein orosomucoid. With a half-life on the order of 6 hours, it is quickly metabolized by liver enzymes to carboxyprimaquine, which does not have anti-malarial activity. Common side effects of primaquine administration include nausea, vomiting, and stomach cramps. Primaquine phosphate is recommended only for the radical cure of vivax malaria, the prevention of relapse in vivax malaria, or following the termination of chloroquine phosphate suppressive therapy in an area where vivax malaria is endemic. Patients suffering from an attack of vivax malaria or having parasitized red blood cells should receive a course of chloroquine phosphate, which quickly destroys the erythrocytic parasites and terminates the paroxysm. Primaquine phosphate should be administered concurrently in order to eradicate the exoerythrocytic parasites in a dosage of 1 tablet (equivalent to 15 mg base) daily for 14 days.

4-Chloroaniline (4-ClA) is a chlorinated aromatic amine that is formed as an intermediate during the microbial decomposition of phenylurea and phenylcarbamate. The formation of various oligomers by polymerization of 4-ClA with guaiacol in an aqueous solution containing oxidoreductases has been reported. 4-Chloroaniline is used as an intermediate in the production of a number of products, including agricultural chemicals, azo dyes and pigments, cosmetics, and pharmaceutical products. Reactive metabolites of 4-Chloroaniline bind covalently to haemoglobin and to proteins of liver and kidney. In humans, haemoglobin adducts are detectable as early as 30 min after accidental exposure, with a maximum level at 3 h. Repeated exposure to 4-Chloroaniline leads to cyanosis and methaemoglobinaemia, followed by effects in blood, liver, spleen, and kidneys, manifested as changes in haematological parameters, splenomegaly, and moderate to heavy haemosiderosis in spleen, liver, and kidney, partially accompanied by extramedullary haematopoiesis. The marketing and use of products containing 4-Chloroaniline based azo dyes were banned by the European Union (EU) (EC, 2000).