How to ShowToast duration parameter not working in Salesforce Lightning Web Component?

handleToast(){
if(this.showToast){
//console.log('calling case comments');
getCaseComment({caseId: this.recordId})
.then(result => {
if(result){
this.dispatchEvent(
showToast('Info','pester', 'Latest Case Comment', result, 75000)
);
}
})
.catch(error => {
console.log('Error occured in showing case comments'+error);
});
}
}

/**
* showtoast event
* @param variant
* @param mode
* @param title
* @param message
* @returns {ShowToastEvent}
*/
const showToast = (variant = 'info', toastMode = 'dismissable', title, message, toastduration) => {
//console.log('dutaion receved >>'+toastduration);
const event = new ShowToastEvent({
title: title,
duration : toastduration,
message: message,
variant: variant,
mode : toastMode
});
return event;
}