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Table 2 List of major drug–drug interactions with their potential risks

From: Potential drug–drug interactions among elderly patients admitted to medical ward of Ayder Referral Hospital, Northern Ethiopia: a cross sectional study

Interacting drugs Number of patients Documentationa Potential risks
Anti TB(HRZ) + phenytoin 2 Good Decreased phenytoin and/or rifampin exposure
Aspirin + cimetidine 1 ND  
Aspirin + clopidogrel 5 Fair Increased risk of bleeding
Aspirin + enoxaparin 2 Good Increased risk of bleeding
Aspirin + fluoxetine 1 Good Increased risk of bleeding
Aspirin + omeprazole 1 ND  
Ciprofloxacin + amitriptyline 1 Fair Increased risk of QT interval prolongation
Ciprofloxacin + doxorubicin 1 Fair Increased doxorubicin exposure
Clarithromycin + amitriptyline 1 Fair Increased risk of QT-interval prolongation
Clarithromycin + amlodipine 1 Excellent Increased amlodipine exposure
Clarithromycin + digoxin 2 Excellent Digoxin toxicity (nausea, vomiting, arrhythmias)
Clarithromycin + nifedipine 1 Moderate fair Increased nifedipine plasma concentrations
Clarithromycin + tramadol 3 Fair Increased risk for seizures, serotonin syndrome, and opioid-related toxicity
Clarithromycin + atorvastatin 1 Good Increased risk of myopathy or rhabdomyolysis
Clopidogrel + cimetidine 3 Fair Reduction in clinical efficacy of clopidogrel
Clopidogrel + diclofenac 1 Excellent An increased risk of bleeding
Clopidogrel + omeprazole 1 Excellent Reduction in clinical efficacy of clopidogrel and increased risk for thrombosis
Cyclophosphamide + allopurinol 3 Good Cyclophosphamide toxicity (bone marrow suppression, nausea, vomiting)
Cyclophosphamide + doxorubicin 3 Fair Increased risk of cardiomyopathy
Heparin + aspirin 14 Fair Increased risk of bleeding
Heparin + enoxaparin 1 Fair Increased risk of bleeding
Heparin + clopidogrel 4 Fair Increased risk of bleeding
Heparin + diclofenac 1 Fair Increased risk of gastrointestinal bleeding
Heparin + indomethacin 3 Excellent Increased risk of gastrointestinal bleeding; reduced effectiveness of indomethacin for the treatment of patent ductus arteriosus
Hydralazine + metformin 1 ND  
Hydralazine + norfloxacin 1 ND  
Insulin + norfloxacin 2 Fair Changes in blood glucose and increased risk of hypoglycemia or hyperglycemia
Insulin + ciprofloxacin 2 Fair Changes in blood glucose and increased risk of hypoglycemia or hyperglycemia
Potassium chloride + enalapril 2 Good Hyperkalemia
Simvastatin + azithromycin 2 Good An increased risk of rhabdomyolysis
Simvastatin + ciprofloxacin 2 Good Increased risk of myopathy or rhabdomyolysis
Spironolactone + digoxin 2 Good Increased digoxin exposure
Spironolactone + enalapril 10 Good Hyperkalemia
Spironolactone + potassium chloride 4 Fair Hyperkalemia
Tramadol + chlorpromazine 2 Fair Increased risk of seizures
Tramadol + amitriptyline 1 Fair Increased risk of seizures, serotonin syndrome (hypertension, hyperthermia, myoclonus, mental status changes), opioid toxicity, and increased concentrations of tramadol and decreased concentrations of tramadol active metabolite
Warfarin + aspirin 3 Fair Increased risk of bleeding
Warfarin + azithromycin 2 Good Increased risk of bleeding
Warfarin + ciprofloxacin 3 Good Increased risk of bleeding
Warfarin + clarithromycin 3 Good Increased risk of bleeding
Warfarin + metronidazole 6 Good Increased risk of bleeding
Total 105   
  1. a Documentation based on available studies or reports: excellent, the interaction has been clearly demonstrated in well-controlled studies; good, studies strongly suggest that the interaction exists except proof of well-controlled studies; fair, available evidences are poor, but the interaction is suspected on the basis of pharmacologic considerations; or, evidences are good for an interaction of pharmacologically similar drug [24]
  2. ND not documented, Anti TB (HRZ) anti tuberculosis (isoniazid/rifampicin/pyrazinamide)