ANTIMALARIAL – INTRODUCTION
Antimalarial drugs are medicines that prevent or treat malaria. A drug directed against malaria.
The original antimalarial agent was quinine which took its name from the Peruvian Indian word “kina” meaning “bark of the tree.” A large and complex molecule, quinine is the most important alkaloid found in cinchona bark. Until World War I, it was the only effective treatment for malaria. In fact, quinine was the first chemical compound to be successfully used to treat an infectious disease.
ANTIMALARIAL – INDICATION
Anti-malarial drugs have been used in various ways to prevent malaria in the resident populations of endemic areas for nearly 100 years. The primary aim of most early studies was to interrupt transmission. This was rarely achieved, but administration of anti-malarial drugs either through medication of salt or by mass administration frequently led to a marked reduction in the prevalence of malaria infection and in the incidence of clinical attacks. Chemoprophylaxis is highly effective in reducing mortality and morbidity from malaria in young children and pregnant women living in endemic areas, but is difficult to sustain and, in some studies, has impaired the development of naturally acquired immunity. Intermittent preventive treatment, in which full therapeutic doses of a drug are given at defined intervals, has the potential to provide some of the benefits of sustained chemoprophylaxis in pregnant women and young children without some of its drawbacks and is a promising new approach to malaria control.
ANTIMALARIAL – INFORMATION
Various drugs are widely used in the prophylaxis and treatment of malaria. In the prevention of malaria in travellers, a careful risk-benefit analysis is required to balance the risk of acquiring potentially serious malaria against the risk of harm from the prophylactic agent. Unfortunately, the information needed to perform accurate analyses of this type is not available for most antimalarials. In the prophylaxis of malaria, chloroquine and proguanil have an excellent safety record, being very rarely associated with severe adverse reactions in the recommended dosages. However, in many parts of the world they are no longer effective prophylactic agents. Pyrimethamine-dapsone (Maloprim) is associated with agranulocytosis, especially if the recommended dose is exceeded, and should be reserved as a second-line agent for travellers to high risk areas. Pyrimethamine-sulfadoxine (Fansidar) and amodiaquine are associated with a relatively high incidence of potentially fatal reactions, and are no longer recommended for prophylaxis. Mefloquine, a relative newcomer, may provoke severe neuropsychiatric reactions with a frequency of 1 in 15,000 to 20,000 users at the prophylactic dosage. In the treatment of Plasmodium falciparum malaria, which has a high mortality if untreated, a greater risk of adverse reactions to antimalarial drugs is acceptable. As chloroquine resistance has become widespread, alternative agents including quinine, mefloquine, pyrimethamine-sulfadoxine, tetracyclines, halofantrine and artemisinin (qinghaosu) and its derivatives may be used in treatment regimens. The therapeutic ratios for chloroquine, quinine and mefloquine are narrow and toxicity is frequent when recommended treatment dosages are exceeded; parenteral administration above the recommended dose range is especially associated with the hazards of cardiac and neurological toxicity.
Minor side effects such as stomach upset and blurred vision occur frequently. These can lessened by taking tablets with food, or taking half the dose on 2 occasions each week. They are safe in pregnant women and children in correct doses. Pruritus (itch) in dark skin individuals is common. . If you have had generalised psoriasis, chloroquine and other chloroquine-like drugs, including primaquine, quinidine and proguanil should be avoided. Retinal changes including eye damage and blindness may occur after prolonged use but on the usual 300mg per week dose it would take 6-7 years.
a combination of atovaquone and proguanil in a single tablet, is a new addition for malaria prevention. Its use has been approved for treatment and prevention of malaria (TGA-Australia) since November 2001. It is particularly useful where malaria is resistant to chloroquine and mefloquine (Larium). On evidence to date, it appears to be very safe and effective, but is expensive.
For prevention of malaria, Malarone is taken once a day, starting 1 day before entering malarial risk area and continuing for 1 week after leaving the malarious area. It should be taken with food or milk. This regime is simple and suited to business & frequent travellers. Nb. When Malarone is used for malaria prevention, side effects are uncommon . However, nausea, vomiting, abdominal pain, and diarrhoea occur when higher doses of the drug are used for treatment. Convulsions and rash have rarely been reported.
It is an alternative to mefloquine for short-term travellers. Doxycycline at 100 mg/day is approved for a period of up to 8 weeks only (NHMRC 1994) but is probably safe for longer use. Side Effects include thrush, stomach & bowel upsets, (particularly if medication is taken on an empty stomach) and sunlight sensitivity. The exaggerated sunburn reaction may be minimised by avoidance of sunlight, using sunscreen and taking the drug in the evening. Drinking copious quantities of water after swallowing the drug is recommended to reduce heartburn. Using Doxycycline may make the Contraceptive pill unreliable. The Therapeutic guidelines 2002 states that: “A second form of contraception is not necessary, but may be offered.” & “Women who develop breakthrough bleeding might consider using barrier methods for the duration of antibiotic therapy”. Discuss this matter with your doctor.
Mefloquine: Side-effects (‘Lariam’) Minor side effects such as nausea, vomiting, heartburn and loose stools occur in about 20% of users, but this is no more frequent than with other antimalarials and usually subside with continued use. Taking ½ tab twice a week with food, and drinking copious water with medication will help reduce these.