Actual drug-drug interactions in elderly patients discharged from internal medicine clinic: a prospective observational study.

PURPOSE: The aim of the study was to evaluate the incidence and type of actual drug-drug interactions (DDIs) that result in adverse drug reactions (ADRs) or diminished therapeutic effect in elderly patients within 30 days of discharge from an internal medicine clinic. METHODS: A prospective observational study was conducted at the Internal Medicine Clinic of University Hospital Dubrava, Zagreb, Croatia, between October and December 2011. Patients aged ≥ 65 years discharged from the Internal Medicine Clinic during the study period with a prescription for two or more medications were eligible for inclusion in the study. A total of 222 patients were ultimately enrolled in the study. For each patient, potential DDIs were identified using Lexi-Interact software. The follow-up visit was scheduled approximately 30 days after discharge. Causality between DDIs and ADRs or diminished therapeutic effect of drugs was assessed by two independent clinicians. RESULTS: Potential DDIs were identified in 190 (85.6 %) patients. Actual DDIs were detected in 21 (9.5 %) patients. In 19 patients, DDIs resulted in an ADR. Diminished therapeutic effect resulting from DDIs was detected in two patients. Angiotensin-converting enzyme inhibitors were the drug class most frequently associated with DDI-related ADRs. CONCLUSIONS: A significant incidence of actual DDIs suggests that DDIs play an important role in patient safety. Drug therapy should be initiated if absolutely necessary, and the number of drugs used to treat elderly patients should be minimized to reduce the incidence of DDI-related adverse patient outcomes.

Enhanced anticoagulant effect of warfarin in a patient treated with cloxacillin.

OBJECTIVE: To present the case of warfarin-cloxacillin interaction that resulted in an increased international normalized ratio (INR). CASE SUMMARY: A 70-year-old man had been treated with warfarin for atrial fibrillation. He was hospitalized because of superficial thrombophlebitis of the left median cubital vein, which developed after venipuncture. An antibiotic therapy with cloxacillin was initiated immediately after the admission. Two days later, INR value increased from baseline 1.9 to 4.6. Anticoagulation therapy was discontinued and INR value was measured daily. His INR remained high for the entire duration of antibiotic therapy. Three days after the cloxacillin therapy was discontinued, the INR decreased to the baseline value. DISCUSSION: In the presented case, the temporal relationship between the administration of cloxacillin and increased INR suggests that the cloxacillin was responsible for the enhanced warfarin activity. According to the Drug Interaction Probability Scale, a causal relationship between the warfarin-cloxacillin interaction and increased INR value was rated "probable". CONCLUSION: Interactions between warfarin and cloxacillin can result in serious adverse reactions. INR value should be closely monitored when patients are prescribed this combination of drugs.

The incidence of potential drug-drug interactions in elderly patients with arterial hypertension.

OBJECTIVE: To assess the incidence and type of potential, clinically significant drug-drug interactions in elderly outpatients with arterial hypertension. SETTING: Three community pharmacies in Croatia. METHOD: Eligible patients were aged 65 or older, treated for arterial hypertension and received 2 or more drugs. Potential interactions were identified by Lexi-Interact software. The software categorized each potential interaction according to clinical significance in five groups: (A) No known interaction; (B) Specified agents may interact, but there is little to no evidence of clinical concern; (C) Specified agents may interact in a clinically significant manner. Monitoring therapy is suggested; (D) The two medications may interact in a clinically significant manner. Modification of therapy is suggested; (X) Contraindicated combination. Interactions of level C, D and X were considered clinically significant. MAIN OUTCOME MEASURE: The incidence and type of potential drug-drug interactions. RESULTS: There were 265 patients included in the study. Potential, clinically significant drug interactions were identified in 240 (90.6%) patients, out of which 97.9% had interactions with clinical significance C, 20.4% D, and 0.8% X. The median number of drug interactions per patient was 4. We identified 215 drug combinations with the potential to cause clinically significant interaction, out of which 83.3% had clinical significance C, 16.3% clinical significance D, and 0.4% clinical significance X. CONCLUSION: Drug-drug interactions are common in elderly hypertensive patients. Computer-based screening could help pharmacists and physicians to recognize potential, clinically significant interactions.

The effect of pharmacotherapeutic counseling on readmissions and emergency department visits.

OBJECTIVE: To evaluate the impact of pharmacotherapeutic counseling on the rates and causes of 30-day post-discharge hospital readmissions and emergency department visits. SETTING: The study was conducted at the Medical Clinic of University Hospital Dubrava, Zagreb, Croatia. METHODS: The study included elderly patients prescribed with two or more medications for the treatment of chronic diseases. The patients randomized into the intervention group received pre-discharge counseling by the clinical pharmacologist about each prescribed medication. The control group received no counseling. MAIN OUTCOME MEASURES: The rates and causes of 30-day postdischarge hospital readmissions and emergency department visits. Medication compliance was also evaluated, using the pill count method. RESULTS: A total of 160 patients were randomly selected for the study. No significant difference was found in the readmission and emergency department visit rates between the intervention and control groups (p = 0.224). There were 34.9 % more compliant patients in the intervention group. Significantly more non-compliant patients in the control group were readmitted or visited emergency department because of the disease progression (p = 0.031). In the intervention group, significantly more patients were readmitted or visited emergency department because of an adverse drug reaction (p = 0.022). CONCLUSION: Pharmacotherapeutic counseling can reduce readmission and emergency department visit rates for disease progression. Improved patient knowledge about adverse drug reactions could be the reason for increased rates of readmissions and emergency department visits due to adverse drug reactions in the intervention group.