Factors that influence choice and quantity of drugs include:

• Population which the health institution serves,
• Disease pattern,
• Seasonal variation in disease pattern,
• Monthly (rate of) drug consumption,
• Knowledge of quantity of each dosage form that is regularly consumed,
• Delivery (lead) time,
• Time lag between placing orders and receiving the orders,
• Request indicator (re-order level):
• Quantity of drug product that serves as a signal for re-ordering.

The maximum quantity of drugs held in stock is determined by:

• Distance from the central health services area or regional medical store,
• Size of the health centre store,
• Number of clients (patients) visiting the health centre.

In this section, three factors-delivery (lead) time, monthly consumption and request indicator-are considered as the basis for calculating the appropriate quantity of a particular drug to be ordered.