Stockouts occur when an entity runs out of inventory or when the customer cannot find the product at the point of sale. There is a lot of research that focuses on solving stockout problems in different industries; however, the amount of such research is very limited with respect to SMEs in the pharmaceutical sector. The purpose of this study was to analyze the main reasons for the existence of inventory problems in pharmaceutical SMEs and to develop a model to avoid them. The study unit was an SME dedicated to the commercialization of retail pharmaceutical products, which had an inventory availability of 76.5%, well below the industry average of 93%. Tools based on Lean Healthcare, EOQ and ABC-VED were used to reduce stockouts. As a result, inventory availability was increased to 87.7%, thus increasing the probability of benefits for the entity and the customer. This encourages to implement the tools in similar cases to improve inventory availability in the pharmaceutical industry, especially in SMEs.