Apart from antidiabetic medications, the most prescribed drug category was antidyslipidaemia medications (75.7%), followed by antihypertensives (69.3%) and antiplatelets (52%). Within the antihypertensives category, angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs) were the most common (78.2%). However, 6.9% of patients who received ACEI/ARB drugs were not hypertensive, with these medications instead prescribed due to their renal protective effects. Atorvastatin (58.7%) was the most frequently prescribed antidyslipidaemia medication, followed by rosuvastatin (39.4%) and simvastatin (1.9%). Of the 155 patients who were prescribed antidyslipidaemia medications, 22 patients (14.2%) were prescribed these drugs for secondary prevention purposes.

There was a significantly higher rate of polypharmacy according to T2DM duration, with patients diagnosed 10 years previously or more having a greater frequency of polypharmacy compared to those diagnosed 5–9 and <5 years previously (62% versus 23.3% and 14.7%, respectively; P = 0.005). Additionally, there was a significantly higher polypharmacy rate among patients aged ≥60 years compared to those aged 50–59 and <50 years (90.1% versus 82.4% and 69%, respectively; P <0.001). Age was also significantly related to the number of comorbidities, with 41.3% of patients aged ≥60 years old having three or more comorbidities compared to 19.1% of patients aged <60 years (P = 0.001). Although women had a higher polypharmacy rate compared to men, this difference was not statistically significant (86.8% versus 78.2%; P = 0.104). However, women did have a significantly higher rate of hyperpolypharmacy (59.3% versus 40.7%; P = 0.011). The likelihood of polypharmacy increased with the coexistence of both hypertension and dyslipidemia (odds ratio = 2.964, 95% confidence interval = 1.395–6.298).

In terms of their self-rated health, 92% of patients perceived themselves to be in good-to-excellent health, with only 8% believing themselves to be in fair-to-poor health. The relationship between polypharmacy and self-related health was not statistically significant (P = 0.233). However, the relationship between self-rated health and the number of co-existing comorbidities was significant, with a higher number of comorbidities associated with poorer health perceptions (P = 0.036). High, medium, and low levels of treatment adherence were reported by 65%, 29.9%, and 5.1% of patients, respectively. Overall, 64.2% of the patients in the polypharmacy group reported high adherence to treatment compared to 67.6% of patients taking fewer medications, with no significant relationship between polypharmacy and adherence to treatment (P = 0.088).

Essentially, pharmacological interventions aim to treat medical conditions using the most appropriate drug. However, polypharmacy can increase the risk of hospitalization, adverse drug events, drug-drug interactions, medication errors, and duplication of therapy, as well as negatively affect the quality of life and healthcare costs [1, 3, 13, 17]. Previous research has revealed that a unit increase in the number of drugs prescribed increases the incidence of drug-related problems by 8.6% [18]. In particular, polypharmacy can endanger the elderly due to impaired renal and hepatic function [2]. Despite these risks, patients still require treatment for coexisting health conditions; moreover, the use of multiple drugs in some cases can be more beneficial than monotherapy [11]. As such, there is some debate over what constitutes appropriate pharmacotherapy for quality assurance monitoring purposes [3].

In the current study, the rate of polypharmacy was high (83.1%) among a sample of T2DM patients attending a family medicine clinic at SQUH. Reported polypharmacy rates in diabetic adults range widely from 54–84%, which may be potentially due in part to the use of different criteria to define polypharmacy [1, 8, 19-21]. Furthermore, various sociodemographic and clinical factors have been associated with polypharmacy, including age, number of comorbidities, and socioeconomic status [3-5, 22]. In particular, older adults (i.e. those aged 60 years or more) have been reported to have higher rates of polypharmacy compared to younger individuals [8, 13-15]. In the present study, polypharmacy was similarly found to increase significantly with age.

Comorbidities play a major role in the number of medications prescribed to diabetic patients [3, 13, 14]. As such, one possible explanation for the association between age and polypharmacy is the greater likelihood of comorbidities within older age groups. Indeed, approximately two-thirds of the T2DM patients in the present study had two or more coexisting chronic health conditions, while just under half were 60 years or older. Similar results have been reported elsewhere in the published literature [13, 23, 24]. For example, Iglay et al. noted that 97.5% of the adult T2DM population in the USA had at least one coexisting chronic disease, with 88.5% suffering from two diseases or more; moreover, up to 82.1% were hypertensive [21].

Another study observed that the prevalence of comorbidities increases with diabetes duration [25]. In contrast, the mean T2DM duration in the present study was very similar in the polypharmacy group compared to the total population. However, this is understandable given the high rate of polypharmacy affecting the vast majority of the total population. Moreover, as health services and drug prescriptions for local citizens are usually free or heavily subsidized in Oman, this may have affected the rate of polypharmacy, with several studies showing that individuals receiving free or inexpensive medical aid are at greater risk of polypharmacy [7, 14].

In the current study, BMI was not found to be significantly related to polypharmacy. While weight increases are associated with polypharmacy, obesity per se is an intermediate confounder and thus cannot be directly related to polypharmacy due to its potential link with other chronic diseases [26]. Moreover, while diabetic women in the present study had a higher rate of polypharmacy compared to men, this association lacked statistical significance. Conflicting results have been published in the literature regarding the effect of gender on polypharmacy [6, 7, 13, 26, 27]. These inconsistent findings may be due to the influence of other factors, such as age, comorbidities, and education level.

In the present study, the most frequent categories of medication administered to T2DM patients were lipid-regulating drugs, antihypertensive and antiplatelet medications. Previous studies have confirmed that these medications are commonly prescribed to diabetic individuals, alongside others like proton-pump inhibitors and nonsteroidal anti-inflammatory drugs [13, 26]. Polypharmacy can result in suboptimal therapeutic effectiveness and poor disease control due to high levels of medication non-adherence [28]. In contrast, the current study observed a relatively high rate of medication adherence (65%) according to the Morisky-Green-Levine score. Using the same tool, Cárdenas-Valladolid et al. observed that 65.7% of homebound elderly patients with polypharmacy were highly adherent to treatment [29]. Other studies evaluating compliance and polypharmacy have used a myriad of tools to assess medication adherence, such as telephone interviews, the Haynes-Sackett test, pill counts, and value judgments [28].

In the present study, the vast majority of T2DM patients (92%) perceived themselves to be in good-to-excellent health. However, a review of the existing literature revealed a dearth of comparable studies evaluating self-rated health in adult diabetic patients with polypharmacy. According to Badawi et al., 78% of diabetic adults in a Canadian community sample rated their health as either good, very good, or excellent, while the remaining 22% perceived themselves to be in poor-to-fair health; however, the polypharmacy status of the population was not assessed.²⁷ In turn, Bazargan et al. studied associations between polypharmacy and self-rated health in a non-diabetes-specific sample of older adults and found that polypharmacy was associated with poor self-rated health and depression [30]. However, it is worth noting that various confounders may play a role in self-perceived health ratings [30, 31].

This study had several strengths, such as the mixed methodology which involved several means of data collection, including a review of patient electronic records as well as face-to-face interviews. This allowed for the inclusion of other medications that the patients may have been taking, including those prescribed by other health institutes or over-the-counter purchases which might not otherwise have been noted in the patients’ medical records. Moreover, assessment of the level of medication compliance and the patients’ self-rated health provided a more holistic picture regarding the effect of polypharmacy on this population.

However, there were certain limitations. Firstly, the study did not include herbal treatments within the criteria for polypharmacy, despite such remedies being widely used in this region [32]. Secondly, the exact clinical indication for each medication was beyond the scope of the study. This would have helped to determine whether polypharmacy was appropriate on a case-by-case basis. Thirdly, the prevalence of medication-related side-effects and drug-drug interactions was not assessed; further studies are recommended to determine how and whether such adverse consequences of polypharmacy affect this population. Fourthly, polypharmacy was considered only if the patient had been taking the drug for over six months; as such, short-term drug use was not evaluated. This may have affected the number of medications used by patients and the overall prevalence of polypharmacy. Finally, actual drug consumption was difficult to measure as the methods used to assess polypharmacy were subjective.

CONCLUSION

Polypharmacy was very common among a sample of T2DM patients at a family medicine clinic in Oman, with both age and diabetes duration found to be significantly associated with this phenomenon. Furthermore, hypertension and dyslipidemia were the most common coexisting chronic conditions and significant predictors of polypharmacy risk. Further research is needed to explore the causal relationship between these variables and polypharmacy. Moreover, additional research assessing the prevalence of drug-drug interactions and adverse drug reactions among T2DM patients is recommended. These findings may be of help to healthcare providers when making prescribing decisions.

ACKNOWLEDGMENTS: The authors wish to thank the original researchers for granting permission to use the Morisky-Green-Levine score in this study.

CONFLICT OF INTEREST: None

FINANCIAL SUPPORT: None

ETHICS STATEMENT: Ethical approval was granted by the Medical Research Ethics Committee (MREC), College of Medicine & Health Sciences, Sultan Qaboos University (MREC approval #1968).