Background Although it can result in serious complications due to its narrow therapeutic index, warfarin is widely used in the treatment and prevention of thromboembolic disorders. However, patients' adherence and knowledge are determinants of therapeutic success. Objective We sought to validate instruments to provide a reliable means of identifying gaps in patient understanding and nonadherence to inform targeted pharmacists' interventions to improve these measures. Methods A cross-sectional survey was conducted. Patients' knowledge about warfarin was rated using an Arabic-language tool. Medication adherence was assessed using the eight-item Morisky Medication Adherence Scale (MMAS-8). The international normalized ratio (INR) control was quantified by the Rosendaal Method. Setting At the Security Forces hospital anticoagulant clinic (ACC), Riyadh. Main outcome measure Validity of a Knowledge and adherence tool. Results Totally, 101 patients completed the questionnaires. Interestingly, the knowledge tool demonstrated good internal consistency (total Cronbach's alpha = 0.75) and significant concurrent validity with adherence levels. Fifty-two patients were classified as having unsatisfactory knowledge. Deficiency in knowledge was most obvious with respect to the consequences of missing a dose and when to seek immediate medical attention. The MMAS-8 had moderate reliability (Cronbach's alpha = 0.65); however, its concurrent validity with good INR control was not demonstrated. Conclusions This study revealed high prevalence of nonadherence and poor knowledge in the population visiting the ACC. Given that available knowledge and adherence tools seemed to have little validity in predicting clinical outcomes, structured tools should be designed, considering progression in clinical outcomes with future pharmacists' interventions.

Pharmacists can no longer ignore the medication use problems encountered by the blind people. This study may serve as an initial step for planning improvements in pharmaceutical services provided to blind patients. The government, pharmaceutical companies and pharmacists must work in collaboration to address the special needs of the blind.

This study provides evidence in favor of the reliability and validity of the Arabic version of TSQM 1.4 as a useful measure of satisfaction with anticoagulant therapy in patients visiting ACCs. The TSQM subscales in this patient setting seem to detect a clinically meaningful change over time, enhancing the potential of their use in routine practice.