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Issue: 2020, December, Volume 14, No 4
issue id: 2020_12_14_4
article id: 2020_12_14_4_8

Original Research

Evaluation of Potential Drug-drug Interactions in the Prescriptions in Outpatient Settings

Evaluation of Potential Drug-drug Interactions in the Prescriptions in Outpatient Settings


Ayaktan Tedavi Edilen Hasta Reçetelerinde Potansiyel İlaç-ilaç Etkileşimlerinin Değerlendirilmesi


Seçkin Engin*1, Elif Nur Barut1, F. Sena Sezen1,2, Ersin Yarış3




Introduction: Drug-drug interactions (DDIs) are an important component of drug-related adverse events, leading to morbidity and mortality worldwide. The aim of the present study was to evaluate the frequency and severity of potential DDIs (pDDIs) in the prescriptions written in outpatient primary care clinics in Trabzon, Turkey. Material and Methods: A retrospective descriptive study was carried out in 169 prescriptions from 15 primary care clinics. pDDIs were identified by using Lexi-Interact™ software program. Results: A total of 169 prescriptions involving 506 drugs were analyzed, of which 59 had at least one pDDI. The prevalence of pDDIs was 34.91%. The mean number of drugs per prescription was 2.99±1.08. A total of 124 pDDIs were identified with mean of 0.73±1.45 per each prescription. Hydrochlorothiazide was the most frequently prescribed drug involved in pDDIs (n=15, 12.10%). The most common pDDIs was between hydrochlorothiazide and metformin (n=4, 3.22%). The number of pDDIs are positively correlated with increasing age (r=0.33 p<0.01) and the number of prescribed drugs (r=0.41, p<0.01). The majority of pDDIs (n=96, 77.42%) were in the risk category C (monitor therapy).  Conclusion: Our findings indicate that polypharmacy and age were associated with the risk of having pDDIs. Physicians and pharmacists should be aware of pDDIs to improve drug safety, patient compliance and, prevent adverse drug reactions. Analyzing of DDIs with softwares should be effective for management of risks associated with pDDIs.


Key words: family practice, interaction, polypharmacy, primary care,  prescription





Giriş:İlaç-ilaç etkileşimleri, dünya çapında morbidite ve mortaliteye yolaçan ilaçlarla ilgili advers olayların önemli bir bileşenidir. Bu çalışmada, Trabzon'da aile sağlığı merkezlerinde ayakta tedavi gören hastalara ait reçetelerdeki potansiyel ilaç-ilaç etkileşimlerinin yaygınlığını ve ciddiyetini değerlendirmek amaçlandı. Materyal ve Metot: Trabzon'da bulunan 15 farklı aile sağlığı merkezinden çıkmış olan 169 reçetede retrospektif tanımlayıcı bir çalışma yapıldı. Potansiyel ilaç-ilaç etkileşimleri Lexi-Interact™ programı kullanılarak analiz edildi. Bulgular: Beş yüz altı adet ilaç içeren toplam 169 reçetenin 59  tanesinde en az bir potansiyel etkileşim saptandı. Potansiyel ilaç-ilaç etkileşimi prevalansı %34.91 ve reçete başına düşen ortalama ilaç sayısı 2.99 ± 1.08 idi. Reçete başına ortalama 0.73±1.45 adet olmak üzere toplam 124 potansiyel etkileşim tanımlandı. Hidroklorotiyazid potansiyel ilaç etkileşimlerinde en fazla yer alan ilaçtı (n = 15,% 12.10). En yaygın potansiyel ilaç-ilaç etkileşimi hidroklorotiyazid  ve metformin arasındaydı (n = 4,% 3.22). Potansiyel etkileşim sayısı ile  hastaların yaşı (r = 0.33, p <0.01) ve ilaç sayısı (r = 0.41, p <0.01) arasında pozitif korelasyon mevcuttu. Etkileşimlerin büyük çoğunluğu C grubu (n=96, 77.42%) risk kategorisine aitti. Sonuç: Bulgularımıza göre polifarmasi ve ileri yaş, potansiyel ilaç-ilaç etkileşim riskini artırmaktadır. Hekimler ve eczacılar ilaç güvenliği ve hasta uyumunu iyileştirmek, ve olumsuz ilaç reaksiyonlarını önlemek için potansiyel etkileşimlerin farkında olmalıdır. İlaç-ilaç etkileşimlerinin yazılımlarla analiz edilmesi, potansiyel etkileşimlere ilişkili risklerin yönetimi için etkili olabilir.


Anahtar kelimeler: aile hekimliği, etkileşim, polifarmasi, birincil  bakım, reçete


Received / Geliş tarihi: 01.04.2020, Accepted / Kabul tarihi: 06.08.2020


1 Department of Pharmacology, Faculty of Pharmacy, Karadeniz Technical University, Trabzon, TURKEY.

2 Drug and Pharmaceutical Technology Application and Research Center, Karadeniz Technical University, Trabzon, TURKEY.

3Department of  Medical Pharmacology, Faculty of Medicine, Karadeniz Technical University, Trabzon, TURKEY.


*Address for Correspondence / Yazışma Adresi: Seckin Engin, Department of Pharmacology, Faculty of Pharmacy, Karadeniz Technical University P.O:61080, Trabzon-TURKEY.

E-mail: seckinengin@ktu.edu.tr

Seckin E, Barut EN, Sezen FS, Yarıs E. Evaluation of Potential Drug-drug Interactions in the Prescriptions in Outpatient Settings. TJFMPC, 2020;14(4): 564-571.


DOI: 10.21763/tjfmpc.713208





Drug-drug interactions (DDIs) defined as an altered response of one drug by concurrent use of another drug,  is a major concern in pharmacotherapy. DDIs may result in adverse drug reactions (ADRs) and decreased or increased efficacy of drugs leading to increased rate of hospitalization, prolonged hospital stay, morbidity, mortality and higher healthcare expenditures. DDIs is one of the most common drug-related problems causing poor patient compliance and decreased quality of patients’ life.1,2


Numerous studies have been conducted to determine DDIs, possible risk factors and potential clinical outcomes. It is well established that age (commonly elderly), number of drugs, duration of combination therapy, drugs with narrow therapeutic index and underlying diseases are the main risk factors for DDIs. Elderly patients are considered to be more prone to develop DDIs due to age-related physiological changes and co-morbid conditions.3,4,5 It has been also reported that the incidence of potential DDIs (pDDIs) is about 40% in patients receiving 5 drugs and 80 % in patients receiving 7 or more medications.6 The incidence of DDIs-related hospital admissions has been estimated to range from 2.8% to 23%.5,7 DDIs are considerable cause of ADRs, accounting for 5-41% of all ADRs.8,9 Therefore, identification of pDDIs could help to prevent ADRs and improve quality of medical care by increasing knowledge and awareness of clinicians.


Many studies based on primary care reports have revealed the prevalence for pDDIs range from 12% to 80%.11 The variations in outcomes of these studies are attributed to experimental design, patient characteristics and DDI software programs.10,11 However, limited data is available on the evaluation of pDDIs in the outpatient settings.  The purpose of this study was to analyze the frequency  and severity of pDDI in prescriptions of outpatients from a selected region in Turkey.





Study Design and Setting


This is a retrospective descriptive study that was designed to evaluate pDDIs in prescriptions randomly reported by the pharmacy students who were doing an internship in fifteen family practice centers in the city of Trabzon, Turkey two half days per week as a part of their mandatory pharmaceutical care course during February to May 2016. Data on patients’ demographic information (age and gender), prescription details and the number of additional drug use (co-administreted drugs out of reported prescriptions) were recorded by the students during that period. A total of 169 prescriptions were analyzed in this study. Prescribed drugs were classified into groups according to Anatomical Therapeutic Chemical Classification (ATC Code) as recommended by World Health Organization.12 pDDIs were analyzed by using Lexi-Interact™, an online software program available on the website www.uptodate.com and pDDIs were also categorized into risk categories named as A (no known interaction), B (no action needed),  C (monitor therapy), D (consider therapy modification) and X (avoid combination) according to the  software.13 For a medicine that contains two or more active substances, each active substance was considered for pDDIs separately. All data were recorded in Microsoft Excel v.2010 spread sheet® and analyzed using  GraphPad Prism 5.0 (GraphPad Software, Inc., San Diego, CA). Data were tested for normality using the Shapiro-Wilk test and presented as mean±standard deviation (SD) or percentage of case. Data were compared by Mann– Whitney U test for continuous variables and the chi-square test for categorical variables when appropriate. Spearman correlation coefficient was used to determine the relationship between two variables.  p<0.05 was considered statistically significant.





Demographic Profile of Patients


A total of 169 patients were included in the study, of which 101 (59.76%) were female and 68 (40.24%) were male. The patients were classified into three age groups as  0-14 years, 15-64 years, and ≥65 years. The mean age of the patients was 42.10±25.20 years and the majority of patients’ age was between 15-64 years old. The age distribution of patients was 0-14 years (n=37, 21.90%), 15-64 years (n=96, 56.80%) and ≥65 years (n=36, 21.30%).


Drug Prescription Details


Totally 506 drugs were prescribed for 169 patients. The mean  number of drugs per prescription was 2.99±1.08, 101 of prescriptions (59.76%) contained at least two drugs, 10 (5.92%) of prescriptions contained only one drug. Three-drug containing prescriptions were the most prevalent (n=63, 37.28%). The highest number of drugs prescribed in a single prescription was 8 (Table 1).







Respiratory system drugs were the most frequently prescribed (n = 78, 15.42 %), followed by the drugs effecting the alimentary tract and metabolism (n=77, 15.22%), and cardiovascular system drugs (n=70, 13.83%). Musculoskeletal system drugs were the most frequently prescribed group for the female patients whereas cardiovascular system drugs were most common in the prescriptions of male patients (Table 2). 







The mean numbers of drugs were for female and male patients were 3.15±0.14 and 2.88±0.09, respectively (Figure 1). No significant difference was found between male and female patients regarding the mean number of drugs per prescription (p>0.05). A weak positive correlation was observed between patients’ age  and the number of prescribed drugs (Spearman correlation coefficient r=0.26, p<0.01).








Drug Interactions


The total of 124 pDDIs were  identified including the additional drugs (drugs were taken by patients, which were out of analyzed prescriptions). Seventeen of total pDDIs were between the additional drugs and currently prescribed drugs. The mean number of pDDIs per prescription was 0.73±1.45. Among 169 prescriptions, 59 had pDDIs ranging from 1 to 11. Thirty (17.75%) of prescriptions had one pDDI. Highest number of pDDIs in a single prescription was 11(Table 3).








The prevalences of pDDIs in prescriptions of females and males were 53.23% and 46.77%, respectively  Prescriptions with one pDDI was common for both genders (Table 4).








The most common drugs involved in pDDIs were hydrochlorothiazide (n=5, 12.10%) followed by metformin (n=14, 11.29%), acetylsalicylic acid (n=12, 9.68%) (Table 5).








The most frequent combinations with a risk of pDDI were hydrochlorothiazide-metformin (n=4, 3.22%), followed by acetylsalicylic acid-ibuprofen (n=3, 2.42%), clarithromycin-salbutamol (n=3, 2.42%) and metformin-ramipril (n=3, 2.42%). The most frequent drug pairs involved in pDDIs  and their potential risk were presented in Table 6.








Based on severity scale, 96 (77.42%) were in the risk category C, 18  (14.52%) were in the risk category B, 9 (7.25%)  in the risk category  D, 1 (0.81%) was in  the risk category X. The only pDDI reported in the risk category X was between dexketoprofen and flurbiprofen. Most of pDDIs (n=80, 64.52%) were identified in prescriptions of the patients aged between 15-64 years (Table 7).








Number of pDDIs was moderately positively correlated with increasing age (Spearman correlation coefficient r=0.33, p<0.01) and number of drugs prescribed (Spearman correlation coefficient r=0.41, p<0.01). Gender was not associated with increased risk of pDDIs (p>0.05, Mann–Whitney U test).





In the present study, we critically evaluated the prescriptions of outpatients of primary care clinics. Our results showed that pDDIs identified in the risk category C is more common in outpatient settings and polypharmacy and increased age are risk factors for pDDIs.


In this study, the mean number of drugs per prescription was 2.99±1.08, which was lower in comparison with previous studies.14,15 In many studies investigating pDDIs, prescriptions with a single  drug were excluded. However, we included one drug containing prescriptions (n=10) in order to analyze pDDIs with patient reported drug use that is not concurrently included in the prescriptions. We found a positive correlation between patients’ age and the number of prescribed drugs, which is consistent with earlier studies.14,15 Based on our results, drugs affecting respiratory system, alimentary tract and metabolism and cardiovascular  system were widely prescribed therapeutic groups accounting for 44.47% of overall prescribed drugs, which is similar to the results of previous studies.16,17


In our study, 59 of total prescriptions had at least one pDDI and the prevalence of pDDIs was 34.91%.  The prevalence of pDDIs in previous studies has been documented in patients ranging from 12% to 80%, which might vary due to sample size, study design, analysis methods of pDDIs and characteristics of the population.10 In prescriptions for female outpatients the prevalence of pDDIs was higher when compared to that of males, which is consistent with the previous study conducted in hospitalized patients.5


In our study, the most prevalent drug involved in pDDIs was hydrochlorothiazide (n=15, 12.10%) that was also reported as one of the most common drugs causing pDDIs in previous studies.18,19 Moreover, the most common pDDIs  identified in this study was between hydrochlorothiazide and metformin (n=4, 3.22%), followed by acetylsalycilic acid and ibuprofen (n=3, 2.42). Hydrochlorothiazide is a thiazide diuretic that is associated with  hypokalemia and hyperglycemia. Therefore, hydrochlorothiazide may reduce the efficacy of  anti-hyperglycemic  drugs  like metformin, which  may require the dose of  anti-hyperglycemic  drugs to be increased. Concurrent use of  hydrochlorothiazide  with certain drugs such as steroids and  beta agonists can also potentiate  hypokalemia or electrocardiography changes.20,21 Acetylsalicylic acid is a member of non-steroidal anti-inflammatory drugs (NSAIDs) that exert anti-inflammatory, analgesic and antipyretic effects by inhibiting cyclo-oxygenase (COX), an enzyme responsible for  prostaglandin synthesis. Co-administration of acetylsalicylic acid and other NSAIDs like ibuprofen could increase the risk of serious gastrointestinal adverse events.22 In many cases of prescriptions we analyzed, acetylsalicylic acid was prescribed for the prophylaxis of cardiovascular and cerebro-vascular events. Acetylsalicylic acid is considered to have less potential risk for DDIs when used at lower doses for the prophylaxis.22 On the other hand, if acetylsalicylic acid and ibuprofen are taken together, both  drugs  can compete for the acetylation site of COX-1 in platelets, resulting in  the blockade of irreversible inhibition of COX by acetylsalicylic acid and thus decrease in the anti-platelet efficacy of acetylsalicylic acid.  FDA recommends that  ibuprofen should be taken at least 30 minutes after aspirin  or at least 8 hours before aspirin to avoid  any potential interaction.23


We found that the majority of pDDIs was in risk category C (monitor therapy), accounting for 77.42% of all. A moderate positive correlation between the number of pDDIs and age was observed. Moreover, a positive correlation was also found between number of  pDDIs and the number of drugs prescribed.  There was no significant difference between genders for the number of pDDIs, which is in agreement with other studies.8,24


We identified only one pDDI between dexketoprofen-flurbiprofen was in risk category X, which means to be this combination to be avoided. Like dexketoprofen and flurbiprofen, concomitant use of  two or more  NSAIDs could increase the probability of GI bleeding.22


DDIs associated with increased risk for hospitalization and ADRs are growing concern in patients receiving multiple medications. Physicians and pharmacists should be aware of the pDDIs to improve patient compliance and drug safety. DDIs should be also included in the continuous vocational education and training programs to increase awareness and knowledge level. The introduction of software analyzing DDIs or lists in hospitals and pharmacies would help to reduce the risks related to DDIs.


We acknowledge several limitations of our study such as short duration, using only one DDI screening tool and small population. Further studies are required with a larger sample population, planning a longer data collection period and using more DDI databases, while increasing the clinical knowledge level and experience and inducing awareness; overall which will help to improve quality and effectiveness of medical care.





In the present study, we reported that the majority of pDDIs was in risk category C (monitor therapy). Moreover, polypharmacy and age were found to be associated with the risk of having  pDDIs. This study now provides preliminary evidence to emphasize the importance of pDDIs in the prescriptions of outpatients in family practice centers. Physicians and pharmacists should be aware of pDDIs to improve drug safety and patient compliance, and prevent adverse drug reactions.





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