Objective Limited data from pharmacokinetic studies in underweight and severely malnourished children have indicated an impaired activity of their hepatic enzymes. We used the caffeine breath test to assess the metabolising activity of cytochrome P450 1A2 (CYP1A2) enzyme in underweight children.

Methods Underweight children from the paediatric outpatient clinic, Lagos State University Teaching Hospital, Ikeja in Nigeria, were studied. After an overnight fast, 15 underweight children took 3 mg/kg labelled caffeine orally. Breath samples were collected in duplicate at −20, −10 and −1 min and at 15 min intervals for 2 h. The mean cumulative per cent dose recovered (CPDR) of labelled caffeine in the expired carbon dioxide was determined over the study period. This was repeated after 2–6 weeks of nutritional rehabilitation.

Results The mean areas under the enrichment-time curve before and after nutritional rehabilitation were 0.539±0.320 and 0.620±0.322 atom per cent excess minute, respectively. The difference between the two values was not statistically significant (p=0.528). The mean CPDR in the exhaled carbon dioxide of the underweight children over a period of 2 h was 7.56±4.01% and 7.95±3.68% before and after nutritional rehabilitation, respectively, and there was no significant difference in the mean values (p=0.603).

Conclusions The metabolism of caffeine was not significantly affected in underweight children compared with after 2–6 weeks of nutritional rehabilitation. This suggests that hepatic CYP1A2-metabolising activity was not significantly impaired in underweight children.