en psychiatry psychiatry Original Article Original Article <span style="font-size: 14px;"><span style="font-family: times new roman;"><span style="color: rgb(0, 0, 255);"><strong><em>Background:</em></strong></span> Major depressive disorder is a severe, heterogeneous, common medical illness and a leading cause of disability throughout the world that poses a significant public health issue. Previous studies have shown rapid antidepressant effects following a single administration of ketamine. This study aimed to assess the impact of route of administration and dose of ketamine for the reduction of depressive symptoms and compare the effects of different doses and methods.<br> <span style="color: rgb(0, 0, 255);"><strong><em>Methods</em></strong><em>:</em></span> A double-blind clinical controlled trial was done on 100 patients with a primary diagnosis of major depressive disorder who were assigned into two groups of 50 subjects at a dose of 0.5 mg/kg and 0.75 mg/kg ketamine and each group was divided into two groups of 25 subjects following a single dose of intravenous bolus and infusion of ketamine. The patient&rsquo;s severity of depression was evaluated with Hamillton Depression Rating Scale and Beck Depression Inventory scores after 2 days, 7 days, 30 days and 60 days of ketamine administration, then the results were compared between groups.<br> <span style="color: rgb(0, 0, 255);"><strong><em>Results:</em></strong> </span>According to Hamilton and Beck score, the treatment response in investigated patients was 64% and 60%, respectively.<br> <span style="color: rgb(0, 0, 255);"><strong><em>Conclusions:</em></strong></span> These data suggest that ketamine effect is related to drug dose and type of administration. The dose of 0.75 mg/kg of ketamine is more effective than 0.5 mg/kg and a bolus injection of low-dose ketamine (0.5 mg/kg) is more effective than infusion and in high-dose ketamine (0.75 mg/kg), there was no difference between the methods of drug administration.</span></span><br> <p></p> Ketamine, Major depressive disorder, Bolus, Infusion 220 227 http://caspjim.com/browse.php?a_code=A-10-748-1&slc_lang=en&sid=1 Farzan Kheirkhah drfarzankh@yahoo.com 100319475328460013539 100319475328460013539 No Social Determinants of Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Gooya Tayyebi g.tayyebi@yahoo.com 100319475328460013540 100319475328460013540 Yes Student Research Committee, Babol University of Medical Sciences, Babol, Iran Seyed Mozaffar Rabiee 100319475328460013541 100319475328460013541 No Cancer Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Ali-Akbar Moghadamnia 100319475328460013542 100319475328460013542 No Cellular and Molecular Biology Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Ali Bijani 100319475328460013543 100319475328460013543 No Non-Communicable Pediatric Diseases Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran