A PAR level in pharmacy is the preset minimum and maximum quantity of a medication that should be kept in stock at any given time. PAR stands for Periodic Automatic Replenishment. When inventory drops to the minimum PAR level, it triggers a restock order. The maximum PAR level prevents over-ordering. Together, these two numbers keep shelves stocked without tying up money in excess inventory.
How PAR Levels Work in Practice
Every medication in a pharmacy gets assigned two numbers: a minimum and a maximum. The minimum is the lowest quantity you can have on the shelf before you risk running out before the next delivery arrives. The maximum is the most you should have on hand, accounting for shelf space, expiration dates, and budget.
When stock of a particular drug falls to or below the minimum, it’s time to reorder. The order quantity is typically the difference between what’s currently on the shelf and the maximum PAR level. So if your maximum for a common antibiotic is 200 tablets and you’re down to 50, you’d order 150. This keeps the cycle simple and repeatable, which matters when a pharmacy manages hundreds or even thousands of different products.
The Basic PAR Level Formula
The most common way to calculate a PAR level uses three variables:
PAR Level = (Average Daily Usage × Lead Time) + Safety Stock
- Average daily usage is how many units of a medication you dispense on a typical day, based on historical data.
- Lead time is the number of days between placing an order and receiving it from your supplier.
- Safety stock is an extra cushion of units to cover unexpected demand spikes or supplier delays.
For example, say your pharmacy dispenses 20 tablets of a blood pressure medication per day, your wholesaler delivers in 2 days, and you want a 1-day safety buffer. Your minimum PAR level would be (20 × 2) + 20 = 60 tablets. You’d want to reorder before inventory dips below 60.
A second approach works better for pharmacies that receive deliveries on a fixed schedule. That formula divides weekly usage plus safety stock by the number of deliveries per week. If you use 140 tablets a week, keep 40 as safety stock, and get two deliveries per week, each delivery should bring you back up to (140 + 40) / 2 = 90 tablets.
PAR Levels vs. Reorder Points
These terms get used interchangeably, but they describe slightly different systems. A reorder point is simply a trigger: when stock drops below a certain number, you place an order. It doesn’t define how much stock you should have after restocking, and it doesn’t depend on a set delivery schedule.
A PAR level goes further. It defines the ideal stock level to maintain after each restocking cycle, and it works best when deliveries happen on a consistent schedule. In practice, most pharmacies use PAR levels because they do receive regular deliveries from wholesalers, often daily or several times a week. The PAR system fits naturally into that rhythm.
How Automated Dispensing Cabinets Use PAR Levels
In hospital pharmacies, medications are often stored in automated dispensing cabinets (ADCs) on patient care floors rather than being dispensed from a central pharmacy for every dose. These cabinets rely entirely on PAR levels to stay stocked. Each medication pocket in the cabinet has a programmed minimum. When nurses pull enough doses to hit that minimum, the cabinet automatically sends a refill request to the central pharmacy.
A study at a large academic medical center examined this workflow across ten dispensing cabinets on internal medicine and medical-surgical floors. The calculated PAR levels were manually programmed into the cabinet software, and each medication was assigned to a specific drawer location based on its quantity and physical size. When stock hit the minimum threshold, a signal went to the central pharmacy, and a technician restocked the cabinet on the next scheduled delivery run. This system reduces the chance of a nurse reaching for a medication and finding an empty pocket, which can delay patient care.
Factors That Affect PAR Level Settings
PAR levels aren’t static numbers. Several factors push them up or down over time:
- Seasonal demand: Flu season drives up usage of antivirals and fever reducers. Allergy season increases demand for antihistamines. PAR levels for these medications should rise during peak months and fall afterward.
- Drug shortages: When a manufacturer reports a supply disruption, lead times become unpredictable. Increasing safety stock for affected medications helps avoid gaps.
- Delivery frequency: A pharmacy receiving daily deliveries can keep lower PAR levels than one receiving shipments twice a week. More frequent deliveries mean less inventory sitting on the shelf.
- Prescribing patterns: If a new physician joins a nearby clinic and frequently prescribes a particular medication, demand shifts. A new treatment guideline can do the same across an entire drug class.
- Expiration risk: Setting PAR levels too high for slow-moving medications leads to waste. If a specialty drug only gets dispensed a few times a month, keeping a large stock means units may expire before they’re used.
How Often to Review PAR Levels
Setting PAR levels once and forgetting them is one of the most common inventory mistakes in pharmacy. Usage patterns shift with seasons, new drug launches, formulary changes, and patient population trends. Most well-managed pharmacies review PAR levels at least quarterly, with more frequent checks for high-volume or high-cost medications.
The review process typically involves pulling dispensing data for a set period, comparing actual usage to the current PAR settings, and adjusting up or down. In hospitals using automated dispensing cabinets, the cabinet software tracks every transaction, making it straightforward to spot medications that are being restocked too frequently (PAR set too low) or sitting untouched between deliveries (PAR set too high). Retail pharmacies often rely on their dispensing software’s inventory reports to do the same analysis.
Getting PAR levels right has a direct financial impact. Overstocking ties up cash in inventory that could be used elsewhere and increases the risk of expired product. Understocking leads to emergency orders, which often come with rush delivery fees, and can result in patients leaving without their medication. The goal is a narrow window between minimum and maximum that matches your pharmacy’s actual dispensing rhythm as closely as possible.