After a year of taking antiretrovirals (ARVs), more than a third of the patients surveyed in a study of Nigeria's treatment programme were not responding adequately to the medication, raising concerns about resistance.
The research, conducted at 12 government ARV sites, recorded a treatment success rate of 82 percent after six months, but when a year had passed, it was found that only 65 percent of the patients had an undetectable viral load.
Those who still had a detectable viral load after six to 12 months of treatment were considered as 'not responding adequately' to the drugs, and more likely to experience treatment failure.
Researchers subsequently investigated resistance levels among the 119 patients who still had detectable viral load levels after 12 months on treatment.
According to Dr Oni Idigbe, head of the Committee on ARV Resistance, which undertook the study, 27 of the 119 patients showed resistance to the three drugs being administered, while 30 showed resistance to two of the drugs and possible resistance to the third.
This was the first research on levels of resistance developed to ARVs, and was requested by the country's health minister in order to evaluate the impact of successive interruptions in the supply of ARV drugs during 2003.
Nigeria has the third highest caseload of people living with HIV/AIDS in the world, after India and South Africa.
In its report, released last month, the committee admitted that the fall in the treatment success rate was significant enough for health authorities to make immediate efforts to address the problem and search for its causes.
"The level of adherence to the treatment has a direct and significant effect on its efficiency," said Idigbe, who also heads the Nigerian Institute of Medical Research.
Nevertheless, he stressed that while measures had to be taken, there was no reason to be alarmed, as the levels of resistance to the life-prolonging medication were still controllable and most patients were still responding positively to treatment.
Although some patients have shown a gradual increase in their resistance to anti-AIDS drugs, Idigbe pointed out that the cause could also be the result of a particularly slow metabolic reaction by the patient to the treatment.
The committee recommended that health officials ensure the availability of sufficient stocks of ARVs and avoid any interruption in treatment to reduce the rate of treatment failure.