pharmacological monitoring of clozapine is extensive as compared to any other psychiatric medication due to its side - effects . most fatal side - effect of clozapine is agranulocytosis , but the prevalence of this complication is around 0.91% . sometimes fatal complication such as hypertension , pericarditis , tachyarrhythmia , and st wave changes mimicking myocardial infarction have also been reported . many of the adverse effects are dose dependent , are associated with speed of titration and tend to be more common at the beginning of therapy . we report a case of a 45-year - old male who developed clozapine induced supraventricular tachycardia ( svt ) during dose titration , which was successfully treated with verapamil . k , a 45-year - old male with no significant past or family history presented with 8 years continuous illness characterized by delusions of persecution , reference , third person auditory hallucinations , and severe socio - occupational dysfunction . there was history of a suicidal attempt 4 years ago in response to distress caused by the auditory hallucinations . on clinical evaluation , he fulfilled diagnostic criterion for paranoid schizophrenia ( international classification of disease-10 ) . he had failed adequate trials of antipsychotics trifluoperazine and risperidone and a course of nine modified electroconvulsive therapies . in view of the treatment resistance , baseline investigations prior to initiation of clozapine inclusive of complete hemogram , fasting blood glucose , lipid profile , liver and renal functions , electrocardiogram ( ecg ) , and electroencephalogram were within normal limits . there was no history of comorbid medical disorders except bronchial asthma without any recent exacerbation . clozapine was initiated at 25 mg with daily increase in dose by 25 mg until a dose of 100 mg with daily monitoring for adverse events . as he was tolerating clozapine well the dose was increased thereafter by 50 mg daily and a dose of 250 mg was reached on the 7 day . at this dose , he developed sudden chills , rigors , fever , and tachycardia on the 8 day of initiation of clozapine . ecg was suggestive of svt with a heart rate of 207 beats / min and echocardiography was normal . verapamil was preferred to beta blockers in view of comorbid bronchial asthma and he was started on 120 mg / day . clozapine was withheld ; however , he had relapse of psychotic symptoms , which necessitated re - initiation of clozapine . patient is on regular follow - up and is in remission on a combination of clozapine and verapamil . patients may develop svt or sinus tachycardia when on clozapine due to its vagolytic property . persistent tachycardia can cause cardiomyopathy or it could be a feature of an underlying myocarditis . cardiac side - effects with clozapine have been described to be associated with speed of dose titration . in a study by ronaldson et al . ( 2012 ) , doses higher than 250 mg in the first 9 days was associated with higher risk of myocarditis . in our case , the patient was tolerating clozapine well until dose of 250 mg was reached on the 7 day . hence , rapid dose titration could be an important factor associated with cardiovascular adverse events with clozapine . drugs of choice in treating svt include adenosine , calcium channel blockers like verapamil and beta blockers . verapamil was preferred to beta blockers in this case due to the presence of comorbid asthma . an earlier report has also described successful treatment of clozapine related persistent sinus tachycardia with verapamil . verapamil may also have an augmenting role in the treatment of schizophrenia , especially when prominent negative symptoms and affective disturbances are present . this case highlights the importance of slow titration of clozapine to prevent cardiovascular adverse effects and potential role of verapamil in treating clozapine - induced svt and its possible augmenting effect on clozapine .
clozapine is known to be an effective antipsychotic for schizophrenia . 
 cardiovascular complications associated with initiation of clozapine include tachycardia , postural hypotension , and myocarditis . 
 factors associated with development of cardiovascular adverse events are not clearly known , and dose titration has been described to be one among the associated risk factors . 
 we report a case of a 45-year - old man with treatment resistant schizophrenia who developed supraventricular tachycardia during initiation of clozapine and discuss the role of verapamil in its successful management .