The growth of human population results more and more medical waste generated by healthcare activities. Typically, if the disposal of the medical waste is done by a medical waste disposal company, a medical waste vehicle visits the healthcare to collect the waste periodically. To minimize the cost, healthcare facilities tend to prefer a low frequency of visits, i.e., until the inventory level reaches the maximum of its capacity, or the age of the waste is at nearly maximum allowance. If some of all healthcare facilities request a visit at a same time, this preference could make some problems for the medical waste disposal company, such as overcapacity or delayed visits to other healthcare facilities because of limited number of available vehicles. In this paper, we integrate Vendor-Managed Inventory (VMI) concept into an inventory routing model to make an optimized medical waste vehicle schedules and routes, whereas the medical waste disposal company has flexibilities to decide the visit schedule and the number of medical waste bags to be carried, as long there is no overcapacity problem and no medical waste aged more than allowed in all healthcare facilities. From the numerical experiments, it shows that by forcing the medical waste disposal company to pick up all medical waste in the inventory for every visit, i.e., reduce flexibility, there is a probability that overcapacity may occurs at the waste disposal facility. Additionally, the total cost is may increased when the flexibility is reduced.