Menikos,
Unfortunately Plasmodium falciparum is constantly evolving and developing resistance to many of the older anti-malarial drugs, especially Chloroquine.
Most of Africa and certainly nearly all tropical countries in Africa, with the exception of Botwswana, Mauritania and Namibia have chloroquine (trade name Paludrine in UK) resistant malaria and taking Paludrine will give very little protection. Paludrine, anyway must always be taken with a weekly dose of Nivaquine. Side effects of these two drugs are stomach irritation, nausea and mouth ulcers. If you are going to an area where you can take Chloroqine (Nivaquine or Avloclor) and Proguanil (Paludrine), the recommended regime is to start taking one week before travelling and continue for 4 weeks after returning. If you are travelling to any of the tropical countries in Africa, the WHO and most tropical medical centres now recommend either one Malarone tablet daily (starting 2 days before you travel and continuing for one week after you return) or one 100mg capsule of Doxycycline daily ((starting 2 days before you travel and continuing for 4 weeks after you return).
Check up on a regular basis what the recommended regime is for the country you're visiting as new drugs are being developed all the time as resistance to old ones is built up. If you're a pilot definitely avoid Mefloquine (Larium) as it can cause depression, anxiety and paranoia in a some people. Definitely stay away from Halofantrine (Halofan) as it has been known to cause irregular heartbeats, even resulting in death.