We assessed the effects of medication knowledge on medication adherence in hypertensive patients at Matero level-1 hospital, in Lusaka City Zambia. We found that hypertensive patients had low level of medication adherence and poor knowledge about antihypertensive drugs. Uncontrolled high blood pressure (BP) was found to be significantly associated with adherence to medication.
The effectiveness to treatment is lowered due to non-adherence to medication and places a significant cost burden on healthcare systems[11, 12].Therefore, non-adherence to medication is a problem in the management of patients with long-lasting diseases such hypertension requiring long‑term treatments [13, 14].
In this study, only 37.5% of patients adhered to their antihypertensive medications. The proportion of adherence to antihypertensive medications in this study was lower than those reported in Pakistan 62.5%[15],Ghana 41.4% [16], Egypt 73.2%[6] , Ethiopia 67% [14], 65.1% China[17] and England 79% [18].The lower level of adherence in our study could be probably attributed to low level of education and old age among the participants as more than half had only attained primary level and above 60 years. Some studies have reported that insufficient patient education influenced medication compliance especially in older patients [19].However, contrary to this study, other studies have reported much lower levels of adherence. For example, in France 33.6%[20], Ethiopia 31.4%[21],China 27.5%[22] and Cameroon 32.3% [23]. Although we cannot offer a plausible explanation for such a finding, it is surprising that France and China which are developed countries and expected to have more educated people had lower levels compared to this study.
This study reviewed that most of the participants had good medication knowledge about the purpose of medication but had poor medication knowledge regarding side effects. This is supported by three previous studies that were conducted in Denmark, USA and Jordan which also reported similar findings [24-26]. Additionally, our study observed that less than half (42.5%) of the participants correctly named their medication. This is conflicting to the finding of a previous study which reported more than half (69.5%) of respondent named their medications correctly[6].The difference in study findings regarding correctly naming the medication could be attributed to the age because the majority of the participants in our study were elderly patients who could easily forget the name of the medicines. Additionally, level of education could have contributed as the majority of participants in our study had attained only primary education.
Generally, our study found that only 8% of the participants had adequate medication knowledge. The medication knowledge score in this study was very poor when compared to medication knowledge reported in Jordan (62.3%) [26] and Turkey (64.5%)[27].The high medication knowledge levels observed in the previous two studies done in Jordan and Turkey could be ascribed to high literate levels of participants as most of them had attained high education as well as relatively young age. High literate levels as well as relatively young age have been reported in some studies to significantly predict the medication knowledge [26-28].
Our study also assessed the independent valuables associated with medication adherence. In the adjusted logistic regression analysis, Individuals with uncontrolled high BP were significantly more likely to have lower medication adherence. This finding is in keeping with other studies [8, 29].In this study, the age, education level and gender were not associated with medication adherence. This is in contrast with some studies which reported that individuals with younger age [8, 30] , high education level [26, 31] and male patients [6] are more likely to adhere to medication. However, some studies have reported that advanced age [13, 32] and female patients [28] are more likely to adhere to medication .
This study found no association between medication knowledge and medication adherence. In disagreement to this study, some studies have found increased medication knowledge to be associated with medication adherence[26, 28]. Regarding the contents of medication knowledge, a study that was conducted in Turkey reported that patients who knew the names, the purpose and side effects of their medications were likely to adhere to treatment [27]. Also, Karaeren et al. (2009) reported that knowing the duration and the purpose of medicine significantly increased the adherence rates while knowing the side effects of medicine reduced the adherence to medication [33] . The findings of the above studies regarding the contents of medication knowledge does not support the findings of the present study in which we found no association between contents of medication knowledge and medication adherence.
The nature of our study may have encountered several study limitations. The inherent nature of the cross-sectional studies are prone to social desirability bias[34]. However, we assured the participants that their responses were not going to be tied to them and the questionnaire was self-administered. The nature of our study may also be predisposed to recall bias and subsequently affect true adherent level[35] . Nevertheless, we adopted the widely accepted Morisky Medication Adherence Scale of measuring adherence which contains carefully selected questions.