Dosing errors of liquid AZT "exceedingly" common and related to poorer HIV health literacy

Dosing errors are “exceedingly” common when adults are preparing paediatric doses of liquid antiretrovirals, results of research published in the online journal of AIDS show. The cross-sectional study involved 316 HIV-positive adult patients, all taking combination HIV therapy. They were asked to prepare 2.5ml doses of liquid AZT (zidovudine, Retrovir) using both a cup and a syringe with appropriate dose markings. Approximately 50% of doses were incorrectly prepared. Higher HIV-related health literacy was associated with a reduced risk of dosing errors.

“Dosing errors were exceedingly common and were associated significantly with lower HIV health literacy,” write the authors. “Our study highlights serious concern as to an adult’s ability to accurately dose infants for PTMCT [prevention of mother-to-child transmission] or child cART [combination antiretroviral therapy], even adults who are receiving cART for their own care.”

Liquid antiretroviral formulations are used for both the prevention of HIV infections in infants and also for paediatric HIV therapy. However, little is known about the ability of caregivers in low- and middle-income settings to accurately administer liquid antiretroviral doses to children. An international team of investigators therefore designed a study to determine the frequency of such errors. They hypothesised that lower health literacy would be related with an increased risk of errors.

The study was conducted in Maputo Province, Mozambique. The population comprised a convenience sample of HIV-positive adults aged between 18 and 49 years. All had been taking combination antiretroviral treatment for at least three months.

Participants were asked to measure a theoretical 2.5ml dose of liquid AZT using both a cup and syringe. The cup had etched marks at intervals of 2.5ml. The syringe had marks at each millilitre interval. A dosing error was a dose that was 20% above or below the 2.5ml dose; a major dosing error was incorrect by a margin of 40% or greater.

HIV health literacy was assessed using a test of literacy and numeracy applied to an HIV care context. The test was marked on a scale of 0 to 16 with higher scores indicating greater literacy.

Data were gathered regarding the participants’ age and education. They were also asked if there were children in their household, and if any were under the age of five years – the age group most likely to require liquid antiretroviral formulations.

The mean age was 35 years and 90% of participants had one or more child in their household, with approximately half having at least one child under the age of five in their home.

Overall HIV health literacy was poor, the median score just 6.7. Scores were strongly correlated with general numeracy and literacy and level of education.

With both the cup and the syringe, 50% of participants made a dosing error, including 28% making a major dosing error. Approximately 90% of errors using the cup involved over-dosing, whereas 58% of errors with the syringe were under-dosing errors.

Higher HIV health literacy scores were associated with reduced odds of any dosing error with a cup (p = 0.03) or syringe  (p < 0.001) and also a major dosing error using both these implements (p = 0.001, p = 0.01, respectively).

The results were similar when the investigators focused on people caring for children aged less than five years.

“Our findings suggest targeted interventions to improve instructions about paediatric liquid ARV dosing are needed to improve paediatric ARV adherence, particularly in settings dependent on liquid formulations,” state the researchers. They suggest the assessment of HIV-related health literacy “could be used in clinic settings to identify caregivers of HIV-exposed/infected children who may benefit from additional dosing instructions or counselling strategies”.