Table 5.

Top 20 QT drug-drug interaction (QT-DDI) along with their levels, therapeutic class and TdP risks of drugs involved in QT-DDIs

QT-DDIs	Therapeutic class		TdP riska		Levels of QT-DDIsb		Frequency
	Drug 1	Drug 2	Drug 1	Drug 2	Severity	Documentation	QT-DDIs: n (%)c
Ondansetron-Prochlorperazine	Antiemetic	Antipsychotic	Known risk of TdP	Not included in listsd	Major	Fair	88 (30.6)
Ciprofloxacin-Ondansetron	Antimicrobial	Antiemetic	Known risk of TdP	Known risk of TdP	Major	Fair	71 (24.7)
Ciprofloxacin-Prochlorperazine	Antimicrobial	Antipsychotic	Known risk of TdP	Not included in lists	Major	Fair	64 (22.2)
Ciprofloxacin-Metronidazole	Antimicrobial	Antimicrobial	Known risk of TdP	Conditional risk of TdP	Major	Fair	10 (3.5)
Ciprofloxacin-Dolasetron	Antimicrobial	Antiemetic	Known risk of TdP	Possible risk of TdP	Major	Fair	6 (2.1)
Dolasetron -Ondansetron	Antiemetic	Antiemetic	Possible risk of TdP	Known risk of TdP	Major	Fair	5 (1.7)
Dolasetron-Metronidazole	Antiemetic	Antimicrobial	Possible risk of TdP	Conditional risk of TdP	Major	Fair	5 (1.7)
Metronidazole-Ondansetron	Antimicrobial	Antiemetic	Conditional risk of TdP	Known risk of TdP	Major	Fair	4 (1.4)
Fluconazole-Metronidazole	Antimicrobial	Antimicrobial	Known risk of TdP	Conditional risk of TdP	Major	Fair	3 (1)
Prochlorperazine-Promethazine	Antipsychotic	Antiemetic	Not included in lists	Possible risk of TdP	Major	Fair	2 (0.7)
Ondansetron-Promethazine	Antiemetic	Antiemetic	Known risk of TdP	Conditional risk of TdP	Major	Fair	2 (0.7)
Metronidazole-Nilotinib	Antimicrobial	Kinase inhibitor	Conditional risk of TdP	Conditional risk of TdP	Major	Fair	2 (0.7)
Dolasetron-Octreotide	Antiemetic	Antidiarrheal	Possible risk of TdP	Not included in lists	Major	Fair	2 (0.7)
Clarithromycin-Ondansetron	Antimicrobial	Antiemetic	Known risk of TdP	Known risk of TdP	Major	Fair	2 (0.7)
Ciprofloxacin-Ketoconazole	Antimicrobial	Antimicrobial	Known risk of TdP	Conditional risk of TdP	Major	Fair	2 (0.7)
Ciprofloxacin-Fluconazole	Antimicrobial	Antimicrobial	Known risk of TdP	Known risk of TdP	Major	Fair	2 (0.7)
Prochlorperazine-Trimethoprim	Antipsychotic	Antimicrobial	Not included in lists	Not included in lists	Major	Fair	1 (0.3)
Prochlorperazine-Sulfamethoxazole	Antipsychotic	Antimicrobial	Not included in lists	Not included in lists	Major	Fair	1 (0.3)
Ondansetron-Tizanidine	Antiemetic	Muscle relaxant	Known risk of TdP	Not included in lists	Major	Fair	1 (0.3)
Nilotinib-Tizanidine	Kinase inhibitor	Muscle relaxant	Conditional risk of TdP	Not included in lists	Major	Fair	1 (0.3)
Metronidazole-Tizanidine	Antimicrobial	Muscle relaxant	Conditional risk of TdP	Not included in lists	Major	Fair	1 (0.3)
Metronidazole-Prochlorperazine	Antimicrobial	Antipsychotic	Conditional risk of TdP	Not included in lists	Major	Fair	1 (0.3)
Metronidazole-Norfloxacin	Antimicrobial	Antimicrobial	Conditional risk of TdP	Possible risk of TdP	Major	Fair	1 (0.3)

AZCERT Arizona Center for Education and Research on Therapeutics, TdP torsades de pointes, QT DDIs QT prolonging drug-drug interactions

^aTdP risk was based on AZCERT QT drugs list

^bLevels i.e., severity and documentation were based on Micromedex DrugReax® classification

^cPercentage calculated in total number of QT-DDIs i.e., 288

^dDrugs involved in QT-DDIs were not included in the AZCERT QT drugs lists