Antibiotic Formulary SelectionOVERVIEW

As with antibiotic resistance, containing the cost of antibiotics is everyone’s responsibility. The main objective is to select antimicrobial agents that provide effective therapy at a reasonable cost. The expenditures for antimicrobial therapy are variable and depend on several factors:

  • acquisition costs of the drug
  • the route and frequency of administration
  • combination therapy
  • the need for monitoring and adjunctive therapy
  • potential side effects and resistance
  • therapy failure

The study of drug costs and their implications is termed pharmacoeconomics. The successful application of pharmaco-economic principles to antimicrobial therapy requires maximizing therapeutic effectiveness while minimizing costs, with the primary emphasis on pharmacokinetic considerations. This article reviews the various pharmacoeconomic factors that affect antibiotic costs in relation to patients and institutions.


The acquisition cost refers to the unit price of an antibiotic to the institution and applies to both orally and parenterally administered antimicrobials. These costs vary considerably from region to region. Considerable differences in expenses within a region are common and vary according to wholesalers’ costs, the quantity purchased, buying group arrangements, and rebate programs based on volume.

Because of the great variability of acquisition costs, I have often referred to the average wholesale prices (AWPs) as published in Red Book. Although many hospitals do not purchase antibiotics at the AWP, this publication is nonetheless a good source of antimicrobial cost comparisons.

In general, older drugs, particularly when their patents have elapsed, are less costly to acquire on a per-unit basis than drugs that are still protected by a patent. On the whole, most antibiotics are considerably less expensive as oral (PO) formulations than as intravenous (IV) preparations. For example, 400 mg of IV gatifloxacin (, Bristol-Myers Squibb) costs approximately $16, but a 400-mg oral tablet costs about $6.