Most participants claimed that they needed an mobile health application for drug dosage calculations and that this application would save time and increase accuracy in calculations. Based on needs assessment of nurses, features such as choosing and searching the drug name, calculation result display, application user help, update and formula display were selected to develop prototype of the mobile health application. Think aloud usability test identified the prototype usability problems; after redevelopment based on usability results, usability problems of the mobile health application were significantly reduced. Then these problems were fixed in development of the final version.
More than half of the participants found it useful to use the mobile health application in patient care. Martinez et al. also found that mobile health interventions were often helpful. This could be due to the ease of use, mobility and cost-effectiveness of mobile health applications. These mobile health applications can also be useful for a number of reasons, such as enhancing user skills, motivation, and trust as well as supporting clinical staff activities[37–39].
Contrary to previous studies[20, 25, 40] that show drug calculation error in actual performance of nurses, in the present study more than half of nurses believed that they rarely made mistake in drug dosage calculations. However, since more than half of people felt the need to have an mobile health application to perform drug dose calculations, the reason for people not reporting errors may be the difference between abstract ideas and their actual performance.
The majority of participants in this study believed that error in calculating drug dosage is harmful to patients. Various studies[13, 15, 41] have shown that drug dosage calculation mobile health application has been able to prevent drug error by people. Mobile health Applications for drug dosage calculation can be used to maintain patient safety and prevent drug errors. Most nurses participating in this study believed that development of a drug dosage calculation mobile health application could increase accuracy of drug dosage calculations. This finding is consistent with a previous study, which pointed to improved accuracy and reduced error in patient care using medication calculation tools.
Studies[43, 44] have shown that if a technology is not useful, users are less likely to use it. Therefore, it is better to utilize the features desired by users in technology development. Using a user-centered design approach in mobile health application development can meet the needs of users and lead to creation of a user-friendly interface. Implementing user needs tailored to their level of technical literacy also facilitates successful access to and acceptance of mobile health.
At the request of more than half of the nurses, references used and links to scientific references related to drug dosage were used in mobile health application development. In this regard, Ownby et al.  showed that mobile health application can contribute to improvement of knowledge about health of people. Since access to scientific references leads to greater knowledge acquisition by users, linking to scientific references can remind nurses of the knowledge they had learned a long time ago. In addition, these features can be useful in lifelong learning to update clinical information to prevent errors in medical system and to improve the quality of patient care. Most of the nurses participating in this study found it necessary to use the mobile health application help. In this regard, Khajouei et al reported that users were dissatisfied with the lack of help in the system. This may be because help provides a description of how to use it and allows for answers to important user questions. Many nurses consider the ability to update the mobile health application an important feature in app development. In their study, Seed et al. showed that failure to update medical application can lead to information being deprecated and consequently misuse of the application. With the advances in knowledge and the possibility of adding new drugs with sophisticated pharmaceutical computing in this area, the mobile health application seems to be able to cover this new information. In this study, personalization was one of the features that lesser proportion of nurses needed to have in the mobile health application. Anastasiadou showed that patients have different needs and characteristics and that mobile health applications need to be personalized. Contrary to Anastasiadou's findings, the reason that fewer nurses request this feature in the present study could be the relative similarity of nursing activities in the intensive care unit. Since user participation in provision of information content provides immediate and rapid access to this information by users, this study conducted a need assessment to list the needed medications. User need assessment not only identifies information needs, it can also be effective in determining how this information is displayed in the system based on user needs. In the present study, the identified drugs which were required by nurses and ICU specialists were classified according to the formula as well as the medication form in the application and approved by the experts when developing the prototype.
A user-friendly mobile health application can also improve the health outcomes of people. Therefore, this study developed the mobile health application based on user needs and evaluated usability of the mobile health application. Among the methods used to evaluate system usability, the methods that involve present users in the real world provide a better understanding of system usability. Previous studies[54–57] have shown that think aloud method identifies many problems related to usability and identifies the root cause of the problems. Thus, this study used think aloud method to evaluate the application and the identified usability problems were solved. According to usability test results, participants had difficulty selecting some options because of the small font size in the mobile health application. In this regard, Moradian et al.  showed that a larger font size in the system could attract more attention to screen elements. There was also some ambiguity in the name and performance of some buttons, which was identified in the usability test. In this regard, Ehrler et al showed that appropriate labeling for items can improve the ease of use of the mobile health application. In addition, Klingberg et al.  found that changes in button design were effective in improving their performance.
This study had Three limitations. First, the questionnaire was distributed only to all nurses working in General ICUs in three teaching hospitals in Kerman. Future studies could provide more accurate results in a broader context, including other intensive care units such as trauma, stroke, intoxication, heart and surgery. However, given that the medications used in all ICUs are often the same, the study in other wards seems to achieve the same results. Second, some of the user needs may not be covered due to the use of questionnaire in determining user needs. In each case, different features were compiled for this questionnaire by reviewing different mobile health applications and expert opinions, and an open question was added to add those that were not considered. Third, following the U.S. sanctions against Iran and an embargo on iOS products, apple removed Iranian apps from its app store. Hence, in this study we could develop the application only for Android. However, most people use the Android operating system.
Application of findings
The results of this study can be used for hospital presidents and policymakers to plan for the use of drug calculator applications in different wards. Drug Dosage Calculator application can be used as a template for developing similar applications for all nursing groups to increase accuracy and reduce error in drug dosage calculation and ultimately patient safety. Moreover, the method used in this study can be used by health program developers to produce usable mobile health applications with appropriate information content and in accordance with needs of their users.