Evaluation of Drug Dose Calculation Ability of Nursing Students: An Interventional Study

Background: Incorrect drug dose calculations by nursing students can cause drug errors and harm patients. Their ability to calculate the correct dosage of drugs consistently need to be evaluated regularly. The objective of the study was to evaluate the drug dose calculation ability of nursing students. Methods: A pre-post interventional study was conducted among 99 undergraduate nursing students studying in 2nd, 3rd and 4th year. Pre-test was conducted using a 20-item self-administered questionnaire on drug dose calculation test followed by a 30 minute lecture on the methods of drug dose calculation. Post-test was conducted using the same questionnaire after a washout period of six weeks. Mean score, standard deviation, frequency and percentage were calculated. Student t test, one way ANOVA and McNemar Test were used for statistical analysis using SPSS version 11.5 at P-value of 0.05. Results: Pre-test and post-test mean score were 10.59 ± 3.00 and 15.36 ± 2.46 respectively. There was 45.04% increase in mean score in the post-test after the intervention and it was statistically signi�cant (P-value < 0.05). None of students scored more than 90% of mastery level in the pretest and 42 students (42.4%) scored more than 90% of mastery level in the post-test. The mean score was highest for third year students in both pre-test and post-test; however, it was statistically not signi�cant (P-value > 0.05). Conclusions: Drug dose calculation ability of the students was poor in the pre-test and it signi�cantly improved after the intervention. The study �ndings highlight the need for regular continuing mathematical and drug dose calculation practice among the students.


Background
Errors in drug dose calculation can be detrimental and costly to patients.Drug dose calculation and basic mathematical skills play a major role in the safe administration of medicines to the patients.Errors in drug dose calculation account for more than 15% of medication errors [1].Studies conducted among doctors, nurses and paramedics have reported that many healthcare providers are not su ciently competent in drug dose calculation [2][3][4][5][6].Poor understanding of the drug concentration expressed in different ways, dose calculation errors and drug administration errors are some of the common incompetence in nurses and other health care workers [7,8].
Nurses play a vital role in different phases of a patient's medication process.Being one of the essential skill, they need adequate competency in drug doses calculation to for administration of medicines safely.
They need to calculate drug dose with complete accuracy and con dence [9].However, they may face di culties in converting ratio, mass concentration and percentage during drug dose calculation.The increased workload, time constraints, distracting environments, lack of resources and inadequate training have signi cant in uence on the process of drug dose calculation among them [10].The medicines are also available in various strengths like percentage and ratio which further complicate the process.
Research has focused primarily on the numbers and types of errors being made by nurses.There is paucity of data on evaluation of drug doses calculation ability among nursing students.A basic knowledge of performing drug calculations would help to design training modules by educators for the nursing students that ultimately leads to safe medication administration.The aim of the study was to evaluate the ability of drug dose calculation among nursing students studying at a tertiary hospital.

Methods
A pre-post interventional study was conducted at College of Nursing, B.P. Koirala Institute of Health Sciences (BPKIHS), Dharan, Nepal from March-May 2019.The study populations was students studying Bachelor of Nursing.The students who gave consent to participate and studying in 2nd, 3rd and 4th year were enrolled.Data were collected using a pre-tested and pre-validated semi-structured questionnaire prepared after reviewing the literature [7,11,12].It consisted of two parts; the rst part contained questions on sociodemographic pro le.The second part of the questionnaire comprised of a 20-items on drug-dose calculation; the rst two questions were for assessing the awareness of the students regarding drug dose calculation and rest of the questions for evaluating their ability to calculate drug doses (Appendix 1).The questionnaire was again tested and validated in 10% of the study sample to make it more reliable and suitable to the study population and those study sample were not be used in the study.
The sample size was calculated to be 99 using formula n = z 2 *p*q/L 2 for nite population where p was 50% at 95% con dence interval and 80% power [13].Total population enumeration sampling method was used.The purpose of the study was explained to the participants and written consent was taken.Pre-test was conducted using the self-administered semi-structured questionnaire.A one hour interactive lecture on drug dose calculation was conducted immediately after the pretest in the Lecture Theater at College of Nursing, BPKIHS.The lecture consisted of theoretical as well as practical demonstration of drug dose calculations related to various dosage forms like syrup, suspension, tablets, injections and various concentrations like percent and ratio.After washout period of six weeks, post-test was conducted using the same questionnaire used for pretesting.The survey was anonymous, calculator was permitted and 30 minutes were given to ll the questionnaire although 20 minutes time was su cient.The students were informed to maintain anonymity in the lling of the questionnaire.The con dentiality of students was maintained.One mark was given for the correct answer and zero for the incorrect and missing answers.
The total score was 18.
The data were coded and entered into Microsoft Excel 2010.The number of correct and incorrect answers were summated.Their scores were converted into percentage and also categorized into less than 90% and more than 90%.Descriptive statistics mean, standard deviation, percentage and frequency were calculated.Student t-test was used to determine statistically signi cant differences between or within groups for continuous data and one way ANOVA test and McNemar Test for categorical data.All the statistical analysis were conducted using SPSS version 11.5.P-value less than 0.05 was considered statistically signi cant.

Results
All study participants were female.Mean age of the students was 21.70 ± 1.311 years.Most of the students (39, 39.4%) were studying in 2nd year (Table 1).score; however, it was statistically not signi cant (P value > 0.05).Those students who have completed their schooling from government school scored higher both in pre-and post-test than those who had completed their schooling from boarding school; however, it was statistically not signi cant (P value > 0.05).The students having 50-75% mark in their higher secondary had got less mean score in the pretest than those with more than 75% mark.After the intervention the mean score of both these group of students increased in the post-test; however, it was statistically not signi cant (P value > 0.05) (Table 2).

Discussion
The ability of undergraduate nursing students to calculate the drug dose correctly and consistently has been a concern for a long time.This was a pre-post interventional study that had evaluated the ability of nursing students to calculate drug dose at a tertiary teaching hospital in Eastern Nepal.Findings from this study con rm that more than most of the nursing students were unable to perform drug dose calculations competently in the pre-test and after the intervention, there was signi cant increase in the ability.
There was statistically signi cant improvement in their awareness regarding importance of double checking of own drug dose calculations and the necessity to check the calculated dose with a second person during the dose calculation.The increased awareness certainly enhances the accuracy in drug dose calculation and help to prevent dug dose related errors.It is of utmost importance to inculcate such culture at the beginning of the nursing education so that they can practice it for rest of their professional career.
Our study showed that the mean score of the students was more than 50% both in pre-test and post-test.Brown found similar results in which the mean score was 75% [14].No one achieved 100% score in pretest and only one-fth of the students scored 100% in post-test.Similar ndings were also reported in other studies [6,15].Errors in drug dose calculation occur either because of the numerical inability of the students to perform basic functions such as addition, subtraction, multiplication, division and use of decimals and fractions or due to their inability to conceptually extract the correct information from the drug dose calculation problems in order to set up the mathematical calculations needed [16].The students who perform poorly on the written tests on drug dose calculations are assumed to have poor skills in practice.Therefore, the nurse educationist should also focus on the education of nursing students regarding accurate drug dose calculations.
Drug dose calculation ability of the students was poor in the pretest in our study which improved in the post-test after the intervention.Other researches also showed that the ability of drug dose calculation of nursing students was poor [16,17].Similarly majority of the nursing students failed on drug calculation test at a 90% pass level in other researches as well [18,19].The students who scored less than 90% may bene t from frequent education and skill test on drug dose calculation that might help to improve their skills in the area and to decrease the potential patient safety issues.Frequent and mandatory drug calculation modules, both practical and theoretical, should be included in the nursing curriculum from 1st to 4th year which will reinforce the knowledge and skill and make them more competent.Higher secondary education with marks more than 75% was associated with better score among the students in our study.Similar ndings were also reported by Grandell-Niemi et al [19].Therefore previous knowledge and experience on mathematical skills should be considered before planning and implementing effective modules on drug dose calculation ability among nursing students.
The educationist should address mathematical skills and concepts, linking numeracy competency with meaning and context and teaching drug calculation formulae and practical calculation examples should be provided for developing the competency in drug dose calculations [20,21].We have to revise effective teaching and learning strategies to support and facilitate nursing students to learn this skill and make them competent [21].Perhaps there is a need for collaboration between the Nursing Council of Nepal and other relevant authority to establish a core set of competencies and good nursing practice for clinical education of nursing health care professionals.It would be more practical to include drug dose calculation related objective problems during service entry examination of nurses.Researches need to be conducted frequently to check the competencies in drug dose calculation of the nursing students as well as nursing personals.With the advent of more accessible and affordable computer and mobile technology, more use of online materials should be encouraged to enhance mathematical skills among nurses.
Our study had some limitations also.The sample size of the study was small.The arithmetical, conceptual and computational errors were not evaluated.Being a single-center study, the ndings may not be generalized to other nursing students studying at different institutions.

Table 1
Socio-demographic characteristics of the participants (n = 99) -test and post-test mean score were 10.59 ± 3.00 and 15.36 ± 2.46 respectively.Both mean pre-test and post-test score were highest for 3rd year students.There was 45.04% increase in mean score of the students in the post-test after the intervention which was statistically signi cant (P < 0.05, Paired sample T test).None of students scored more than 90% of mastery level in the pretest whereas 42 students Before the intervention, only 85 (85.8%) students agreed that it is necessary to double check our own drug dose calculations; however, after intervention 95 (95.9%) students agreed to this statement which was statistically signi cant (P value < 0.05).Similarly before intervention, only 50 (50.5%)studentsagreedthat it is necessary to check the dose with a second person during drug dose calculation and after intervention 65 (65.6%)students agreed to the statement which was statistically signi cant (P value < 0.05, McNemar Test).Pre-test and post-test score of the students ranged from 4-16 and 8-18 respectively.No one scored maximum score in pre-test; however, only 18 students (18.2%) achieved maximum score in the post-test (Fig.1).

Table 2
Correlation between baseline variables and mean score obtained by the students (n = 99) *One way ANOVA test; $ Student t test