Demographic characteristics

Prescription charts of 250 geriatric patients, 60 years and older, were reviewed for this research study. The demographic information obtained from the reviewed prescription charts included age, gender, and type of prescriber contact, i.e., primary patient contact with either a level 2 prescriber (regional hospital doctor) or a level 3 hospital doctor (specialist prescriber). Other demographic information such as educational status, employment history, income, and patient’s race could not be ascertained or verified as the research study was retrospective and did not include patient contact or interviews.

The average (SD) age in years of sampled geriatric patients was 69.72 ± 7.22. The majority of the sample population were female, 67.6% (n = 169), with males comprising 32.4% (n = 81). This resulted in a female to male ratio of 2:1 and a potential limitation for the differences in results between females and males observed in this research study.

Furthermore, with regards to the type of prescriber contact and reviewed patient population, 74.8% (n = 187) of reviewed prescription charts contained medications ordered primarily by level 2 prescribers, while 25.2% (n = 63) of reviewed prescription charts contained medications ordered by level 3 or specialist prescribers.

The demographic characteristics of the study population are presented in Table 1.

Table 1 Summary of demographics and clinical variables

Prescription chart variables

The variables extracted from reviewed prescription charts included the following: the number of diagnosed clinical problems (acute and chronic), the number of prescribed medications, and the number of potential drug–drug interactions identified according to the clinical severity and mechanism of actions.

The number of diagnosed clinical problems

The prescription charts of sampled geriatric patients, 60 years and older, produced 844 diagnosed clinical problems with an average (SD) of 3.54 ± 1.26. Hypertension (n = 223; 25.2%), diabetes mellitus (n = 146; 16.5%) and dyslipidemia (n = 97; 10.9%), accounted for the most diagnosed clinical problems.

The data presented in Table 2 represents the total number of diagnosed clinical problems identified in this research study per age category and gender.

Table 2 Total number of diagnosed clinical problems per age category and gender

The number of prescribed medicines

One hundred and thirty-six (136) medicines classified by pharmaceutical preparation was prescribed for the geriatric patient population reviewed for this research study. These medicines consisted of varied combinations of oral tablets, topical preparations, inhalants (e.g., nasal sprays and nebulizers), parenteral formulations (e.g., Insulin), liquid preparation, and ophthalmological formulations. Figure 1 represents the distribution of prescribed medicines by pharmaceutical formulation.

Fig. 1
figure1

Prescribed medicines by pharmaceutical formulation

The total number of prescribed medicines for this research study was 3032 with an average (SD) of 12.13 ± 4.25. Female geriatric patients were prescribed an average (SD) of 12.45 ± 4.51, while the male geriatric patients received on average (SD) 11.46 ± 3.58 prescribed medicines.

The number of potential drug–drug interactions

According to the data extracted from reviewed prescription charts, 63.9% (n = 87) of prescribed medicines classified by pharmaceutical formulations were oral tablet formulations, equivalent to 78.9% (n = 2394) of all prescribed medicines. The oral tablet formulations were subsequently analysed for the occurrence of potential drug–drug interactions, PDDIs, using the free online multidrug interaction checkers, Epocrates, for clinical severity of action due to a large medicine reference database [30]. These interactions are described as minor (caution advised), moderate (monitor or modify treatment), major (avoid or use alternative), and contraindicated interactions [30, 31]. Medscape drug interaction checker was used for the analysis of the mechanism of action, i.e., pharmacodynamic, pharmacokinetic, and unknown interactions, due to a definite indication for the type of mechanism of action compared to Epocrates.

The analysis for potential drug interactions per prescription chart produced 2570 PDDIs with an average (SD) of 10.30 ± 7.48 per patient from 95.4% (n = 83) of oral tablet formulations. One liquid preparation was included in the analysis due to the active ingredient in the preparation, morphine sulphate.

The most-prescribed oral tablet formulation for this research study was paracetamol, appearing on 73.6% (n = 184) of prescription charts with a frequency of 210 involvements in PDDIs. However, aspirin was responsible for the most PDDIs (n = 559) although the medicine was prescribed 157 times (62.8%) compared to paracetamol, 184 times (73.6%) (Fig. 2).

Fig. 2
figure2

Prescribed oral tablet formulations and the number of involvements in PDDIs

Potential drug interactions by severity and mechanism of action

The total number of PDDIs identified in this research study was 2570. Potential interactions by clinical severity of action produced minor (n = 350; 13.6%), moderate (n = 1863; 72.5%), major (n = 349; 13.6%) and contraindicated interactions (n = 8; 0.3%), while PDDIs by mechanism of action produced pharmacokinetic (n = 604; 23.5%), pharmacodynamic (n = 1882; 73.2%) and unknown interactions (n = 84; 3.3%).

A summary of interacting drug pairs identified in this research study with a probability of clinical significance (i.e., major interactions, which is described as drug interactions that require routine clinical intervention or therapeutic dose monitoring to minimize or prevent adverse effects that may be fatal or detrimental to a patient’s overall health and contraindicated interactions, which is described as drug interactions which produce clinically significant drug interactions and are discouraged in clinical practice due to the potential for severe adverse reactions) is presented in Table 3.

Table 3 Summary of interacting drug pairs with a potential for clinical significance—major and contraindicated drug interactions

Reviewed associations between variables

Polypharmacy and geriatric patients

The level of polypharmacy for this research study was determined by the average number of medicines prescribed within a particular age category. Geriatric patients within the age-categories, 60–64 (12.39; n = 954; 31.5%) and 70–74 (11.97; n = 766; 25.2%) years of age had the highest levels of polypharmacy compared to the other age-categories reviewed in this research study. The level of polypharmacy was also determined to be highest among the female geriatric population with females receiving an average of 12.45 prescribed medicines (n = 2104; 69.4%) compared to males, 11.45 (928; 30.6%).

A chi-square analysis (p < 0.05) between the variables, gender and polypharmacy was considered statistically significant, χ2 (1, n = 250) = 6.177, p = 0.013. Therefore, a significant relationship was confirmed between gender (females) and the occurrence of polypharmacy according to the results of this research study.

The number of prescribed medications and potential drug–drug interactions

Two hundred and forty-one (241) prescription charts reviewed produced at least one PDDI with an average of 10.30 (SD ± 7.48) potential interactions.

A chi-square statistical analysis (p < 0.05) to determine a potential relationship between the number of prescribed medicines and the occurrence of PDDIs was determined to be statistically significant, χ2 (1, n = 250) = 14.42, p < 0.05, therefore, confirming a positive relationship between the number of prescribed medicines and the occurrence of PDDIs according to the results of this research study.

The number of prescribed medications, potential drug–drug interactions, and type of prescriber contact

The prescription charts sampled for this research study with medications ordered primarily by level 2 prescribers (n = 187) produced 2193 prescribed medicines with an average (SD) of 11.44 ± 4.08 and 1771 PDDIs with an average (SD) of 9.19 ± 7.05. Geriatric prescription charts with medications ordered by specialist or level 3 prescribers (n = 63) produced 893 prescribed medicines with an average (SD) of 14.17 ± 4.14 and 853 PDDIs with an average of 13.57 ± 7.82.

A chi-square analysis (p < 0.05) to determine potential associations between prescriber contact and the number of prescribed medicines, χ2 (1, n = 250) = 11.62, p < 0.05 as well as prescriber contact and the number of PDDIs, χ2 (1, n = 250) = 5.99, p < 0.014, was statistically significant. Therefore, a positive bivariate relationship was confirmed between the type of prescriber contact (i.e., level 3 or specialist prescriber) and the number of prescribed medicines as well as the occurrence of PDDIs.

Multivariate test of associations between variables

A summary of significant results from the chi-square test of associations (chi-square, p < 0.05) between the reviewed variables is presented in Table 4.

Table 4 Summary of results from chi-square tests to determine significant relationships

According to the results of the statistical tests presented in Table 4, significant associations were confirmed between variables; the number of prescribed medicines, type of prescriber contact, and the outcome variable, i.e., the occurrence of PDDIs. Therefore, to determine the existence of a significant multivariate relationship between the dependent variables, i.e., the type of prescriber contact and the number of prescribed medicines towards the outcome variable, i.e., the occurrence of PDDIs among the sampled geriatric patient population, a multiple regression analysis was conducted and the results are presented in Table 5.

Table 5 Model summary from multiple regression analysis of variables

The results in Table 5 show that the number of prescribed medicines together with the type of prescriber contact significantly predicts the occurrence of PDDIs, F (2, 249) = 68.057, p < 0.05, therefore, confirming a mutual multivariate association between polypharmacy, type of prescriber contact, and occurrence of PDDIs.

However, further analysis to determine the relative strength or contribution towards this mutual association as co-variables, showed that the number of prescribed medicines or polypharmacy was the strongest contributor towards the occurrence of PDDIs with a standardized coefficient beta of 0.583 (statistically significant, p < 0.05). The type of prescriber contact was statistically insignificant (p value = 0.467), providing a weaker contribution as a co-variable towards the occurrence of a PDDI according to the results of this research study.

The summary of the analysis showing the relative contribution of the variables; the number of prescribed medicines (polypharmacy) and the type of prescriber contact towards the occurrence of PDDIs are presented in Table 6.

Table 6 Relative contribution of significant variables towards the occurrence of PDDIs

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