Background Medication errors are known to be a widespread problem affecting patient safety and treatment efficacy. We were approached by a Guatemalan clinic interested in piloting an app to aid their junior clinicians in correctly calculating medication dosages.

Methods We programmed a medication-dosing app using CommCare. In a prospective study among junior physicians at a small high-throughput clinic, we primarily assessed the app's dosing accuracy and efficiency. Secondarily, we measured the app's usability and effect on patient-centredness.

Results Six clinicians aged 21–24 tested the app. Among 366 prescriptions, dosages were 40% more likely to be correct when calculated using the app (relative risk: 1.39; 95% CI 1.16 to 1.68; p=0.0005). Accuracy improved from 64.7% (N=156) to 92.4% (N=210). Using the app in a time-constrained context improved clinician efficiency by over 20% with a decrease in average consultation time of 1.5 min (p<0.0001) to 5.23 min on average (N=178). However, questionnaires revealed most clinicians did not believe the app improved efficiency, and none thought its recommendations were ‘always accurate’. No change in patient-centredness was observed (N=167).

Conclusions The app was shown to be safe and efficient. Making this app available to junior physicians may significantly improve patient safety by enhancing dosing accuracy. This study demonstrates that dosing apps can be an efficacious means of decreasing medication errors in developing countries. We found that different strategies to introduce novel apps to providers might improve providers’ trust in the technologies and thereby make apps more efficacious.