Nelfinavir (Viracept) is available in a powder form for children. It is safe and effective, and is approved for use in children aged three years and over^[1]. Children over 13 years should take nelfinavir tablets rather than the powder.

Each gram of the powder contains 50mg of nelfinavir. The recommended dose is 50 to 55mg/kg twice daily or 25 to 30mg/kg three times daily. Children over 13 years of age should take the adult dose of nelfinavir tablets.

The powder can be mixed with water, milk, jam or milk-based desserts, but mixing with fruit juice creates a bad taste. The PENTA 5 study found that most children did not like nelfinavir powder, which produces a lumpy consistency when mixed with milk or food^[2]. In that study and in PENTA 7, many children switched to nelfinavir tablets, which were crumbled and mixed with food or drinks^[3]. As nelfinavir powder contains aspartame, it is not suitable for patients with phenylketonuria.

Therapeutic drug monitoring can be conducted to check drug levels in the blood. One study has shown that maintaining drug concentrations above 0.8mg/l in children improves the likelihood of virological success^[4]. Children with a genetic polymorphism in the gene for poly-glycoprotein have higher blood levels of nelfinavir and are more likely to suppress viral loads^[5].

As in adults, the mutations D30N and L90M are associated with resistance to nelfinavir in children. However, younger children seem more likely to develop L90M, particularly if they have higher viral loads^[6].

Although nelfinavir has not been approved for use in children below three years of age, two recent studies have demonstrated that the following combinations are effective in infants below three months of age:

• Nelfinavir, d4T (stavudine, Zerit) and ddI (didanosine, Videx / VidexEC), although this has a high rate of virological failure^[7].
• Nelfinavir, d4T, 3TC (lamivudine, Epivir) and nevirapine (Viramune). This combination can bring about viral suppression for up to four years in the majority of infants treated^[8].

One small study has investigated the use of anti-HIV combinations including nelfinavir at 40mg/kg twice a day or 10mg/kg three times a day in infants aged less than six weeks. Although these doses were well tolerated, the doses were often too low to produce adequate blood levels of the drug^[9].