MEDICINE INVETORY CONTROL BY CONSIDERING EXPIRY PERIODS AND PRODUCT RETURNS USING THE ALWAYS BETTER CONTROL (ABC) ANALYSIS AND THE HANDLEY WITHIN MODEL OF ECONOMIC ORDER QUALITY (EOQ) AT PHARMACIES IN INDONESIA

This study aims to control medicine inventories by considering the expiration period and the product return using The Always Better Control (ABC) analysis and The handley within model of Economic Order Quantity (EOQ). The results of this study indicate that there are 21% of medicines or 22 types of medicines belonging to group A with the use of 74.64%. for group B there were 25% drugs or 28 types of drugs with a budget use of 15.31% of all medicines. Meanwhile, there are 55% of medicines or 60 types of medicines belonging to group C with the use of a budget of 10.05% of the total medicines and the calculation using the EOQ method by considering the expiration period and product returns in this research has a more optimal order size compared to the previous method so that it can minimize expired medicines and estimate which medicines will expire at the end of the cycle so that the total cost of supplies at the pharmacy is more optimal.


INTRODUCTION AND LITERATURE REVIEW
The development of increasingly modern science and technology has made competition between companies tighter, along with the many new companies that have sprung up in the same industry. The pharmaceutical industry is one of the industries that continues to grow with intense competition, namely the pharmacy. the tight competition of pharmacies so that good operational management is needed to keep the business running. Good management by carrying out an efficient, effective, and economical inventory planning. Pharmacy is included in the category of trading companies because its main activity is to purchase drug supplies from drug distributors or suppliers to be resold to consumers without changing the form or function of the goods. So that the role of supply is an important component in pharmacy operational activities (Rachmawati, Syafirullah, & Faiz, 2020). According to (Apriyani & Muhsin, 2017) Inventory control is an activity in managing inventory to suit your needs and remain stable.
And currently drug checks are carried out every day by the pharmacy and it is known that the demand for generic drugs in pharmacies is quite high, but it is not balanced with good inventory control so that inventory control is not optimal. To place an order, the pharmacy only looks at previous medicine consumption and orders are made when the medicine has reached a supply crisis limit. And because medicine is a perishable product category where the value of the product will decrease over time or cannot be used again if it has passed its expiration date. So if there is a medicine that has passed the expiration limit or damage will cause high inventory costs. And medicines that are not in demand until a certain time limit will be returned with several conditions from the distributor. If the requirements for return are not met, the medicine cannot be returned so that the medcine will be destroyed with the cost of destruction being borne by the pharmacy which results in losses for the pharmacy. The above problems can be avoided if the pharmacy manages to control medicine supplies properly. So far, pharmacies have not carried out inventory control calculations by considering product expiration and returns. to find out the types of medicines that require close supervision in terms of inventory, the size of the order that should be made and the right time to reorder so as to minimize the total cost of supplies.
Several previous studies on medicines supply control are (Nafisah, Puryani, & Lukito, 2011) where in that study developed an EOQ model for pharmaceutical products by considering the expiration period and product returns. And research (Buwono, Priyandari, & Jauhari, 2014), (Hermanto, Indrajaya, & Suhendar, 2018) which only developed the EOQ method in their research so that it was developed again by (Resmana & Rukmayadi, 2019), (Ulfa, Said Salim Dahda, & Widyaningrum, 2018). For research (Dyatmika & Krisnadewara, 2017) by adding the ABC method to classify goods based on investment. From the limitations of previous studies, researchers finally developed it again (Alfanda, Pujotomo, & Wp, 2018) using the EOQ and ABC methods by considering the expiration period and product returns.

RESEARCH OBJECTIVES
The purpose of this study is to classify medicinal products based on the level of importance and size of investment, determine the optimal order size and estimate the medicines that will expire at the end of the cycle so as to reduce the total cost of supplies by using the ABC analysis and Economy Order Quantity (EOQ).

RESEARCH METHODOLOGY AND DATA ANALYSIS
This research begins with a preliminary study, namely a field study, conducting interviews with the person in charge and employees at the pharmacy to obtain information and data needed in the study. Then identify the problem and determine the purpose of the research, then collect data that will be used in the research, then proceed with processing the data that has been developed and then carry out analysis, finding and interpretation.

Model Formulation
Based on previous research (Alfanda et al., 2018), researchers will perform data processing with different case studies, where in this study a probabilistic EOQ model for pharmaceutical products was developed by considering the expiration period and product returns so as to prove that the method used can minimize inventory costs. The assumptions used in this study are as follows: 1.
Demand is probabilistic because disease cannot be predicted 2.
Constant order size for each order, ordering is only made when inventory reaches reorder point (r).

3.
Constant price of goods (P) both to the quantity of goods ordered and time.

4.
Shortage of inventory is calculated by backorder.

5.
Order charge (A) is constant for each order regardless of the quantity ordered. 6.
The cost of holding is proportional to the amount of inventory. 7.
The expiration period is known. 8.
Drugs that have expired cannot be resold. 9.
Medicines that can be returned to suppliers before the expiration date 10. The medcines returned will be replaced with the same drug with a longer expiration period. 11. If the medicine is less than one lot, the drug cannot be returned to the supplier. 12. Medicines that have expired will be worth Rp. 0.,

Grouping Medicine Based on ABC Analysis
This method is an analysis that is used solely to sort the number of uses, then classify the types of goods in an effort to find out the types of goods in an effort to find out the types of medcines movement which include various types, lots of quantities and different patterns of need (Assauri, 2004). The steps in processing medcines grouping data based on ABC analysis are as follows: The steps are : 1.
Determine the number of items for each type of item 2.
Determine the price per item for each type of item 3.
Multiplying the price per item by the number of units to determine the total investment value of each type of item 4.
Arrange the order of the types of goods according to the amount of the total investment value, where the largest total investment value is in the first order.

5.
Calculate the cumulative percentage of goods from the many types of goods 6.
Calculate the cumulative percentage of the investment value of goods from the total investment value.

7.
Grouping classes based on the percentage of goods and the percentage of the investment value of goods.

Handley Within Economy Order Quantity model
Economic Order Quantity (EOQ) is a number of inventory items that can be ordered during a period for the purpose of minimizing the cost of these goods (Sabarguna, 2004). According to (Sukanta, 2017) to determine the value of q) * and r *, it is searched using Handley Within model with lost sales using iteration. The first step that must be taken is to calculate the q value with the Wilson formula, as follows: The values for f (Zɑ) and ψ (Zα) are obtained from the Standard Normal Deviation table. Then the value of q * 2 is obtained, so the value of r * 2 can be determined with the same steps. After the r * 1 and r * 2 values are obtained, the two values can be compared, if the two values do not have a significant difference and are almost the same then the shrimp paste is finished. Conversely, if the value is significantly different, the processing is continued with the next iteration with the same rate. r here is denoted by the reorder point. Where the reorder point according to (Rangkutty, 2017) is the limit or point of the number of reordering including the demand desired or needed during the grace period follows:

Expected Amount of Expired Products at the end of the cycle (ER)
= ℎ (ℎ+ ) (7)

Number of Product Returns
Product returns can be made if there are still s products, where s is the quantity of the product per lot. w is the number of lots that can be returned and w is a positive integer. Since w is the unit of return, only the ER that can be calculated is as follows:

Medicines Grouping Based on ABC Analysis
Medicines group Furthermore, the EOQ analysis was carried out. The data used in the EOQ calculation are ordering costs which include telephone costs, quota costs, paper costs. So that the total of each message in this study is Rp. 10,860. For a saving cost of 20% of the purchase price for one drug item. Where the saving cost is the cost that arises when the company stores the product in a warehouse storage area (Vrat, 2014 According to (Heizer, 2010), along with the increase in the quantity of goods ordered, the number of orders per year will decrease but the storage cost will increase because the amount of inventory that must be taken care of is more. And based on the results of the above calculations, it is known that for the example Herbesser CD 200mg the order interval is 0.066 years or 24 days. The optimal order lot for this item is as in equation (1) and an example of calculating the optimal ordering quantity on Herbesser CD 200mg with 1200 requests is 79 items.
Tabel 3 of the period for all generic medicine groups starting from 2 -344 items. Then the drug that will expire can be returned to the supplier with a maximum of 10 items. and by calculating using EOQ can reduce the total cost of inventory by 9.6% or Rp. 57.547.587,-