Although amodiaquine is an older malaria treatment, little was known about how safe it is in pregnant women.

But researchers at the London School of Hygiene and Tropical Medicine who treated 900 pregnant women in Ghana with the drug found it eliminated the malaria parasite without causing any serious side effects.

"Previous studies had already found amodiaquine alone or in combination with sulphadoxine-pyrimethamine (SP) to be an effective treatment of malaria in children in west Africa, but our research confirms that this is also true for pregnant women," said Professor Brian Greenwood who reported the findings in The Lancet medical journal.

Malaria, a parasitic disease transmitted by mosquitoes, kills more than a million people a year, mostly young children in Africa.

Chloroquine had been the standard treatment against the disease. But the malaria parasite has become increasingly resistant to chloroquine and SP.

The World Health Organisation (WHO) has urged African nations to switch to artemisinin-based combination drugs known as ACTs but doctors have been concerned about the effects of the treatment on the developing foetus.

The researchers said weakness, vomiting, dizziness and nausea were the most commonly reported side effects.

"Amodiaquine is safe if it is used properly and it is one of the drugs that is available for us to use in Africa," said Dr Harry Tagbor, a co-author of the study from St Theresa's Hospital in Nkoranza in Ghana.