Some may argue that more drugs are being developed in areas where the benefits to the society are maximized whereas others may claim that the direction is led to where the economic incentive for the pharmaceutical industry is higher [2]–[5]. A third reason may be a mounting social pressure from rising prevalence and incidence of certain health problems. Other reasons, which may influence drug development, may include the failure of current medications to solve existing health problems or the identification of new diseases such as the highlighted example of AIDS. The problem of new drugs–usually more expensive - substituting for older ones with similar chemical structure, which are loosing patent privileges, is thought to be one of the factors contributing to the increasing annual drug expenditure around the world.

The problem of shortage of new anti-microbial agents has been well described in the medical literature [6]. This disturbing fact is occurring despite the gradually increasing prevalence of microbial resistance to existing antibiotics in various parts of the word [7]–[9]. A significant reduction (56%) of new approvals of antibacterial agents occurred during the period 1998–2002 compared to the period 1983–1987. In addition, the fact that only 6 out of 506 drugs disclosed in the development programs of the largest pharmaceutical and biotechnology companies are antibacterial agents is really distressing [10].

In order to conduct our analysis, we classified each new drug in one of sixteen main therapeutic categories. However, four therapeutic categories were excluded from further analysis because of the small number of new drugs developed in each category. The excluded categories were: contrast agents [including 3 new drugs (Tc-99m depreotide, Tc-99m apcitide, and human albumin microspheres)], antidotes [including 1 new drug (fomepizole)], ear, nose and throat drugs [including 1 new drug (cevimeline)], and anesthesiology drugs (there was no new medication in this category during the study period). In addition, urea C-14 was not included in the gastrointestinal category since it is used exclusively for diagnostic purposes.

The median drug cost of a ten-day treatment of an antineoplastic agent was actually more than 6 times higher than the respective value in the category of antimicrobial agents; the difference is even more pronounced if someone excludes from the category of new antimicrobials, the drugs for the management of HIV infection. In fact, anti-neoplastic agents are given in prolonged cycles of chemotherapy and it is, therefore, reasonable to assume that our analysis actually underestimated the true drug cost of treatment for anti-neoplastic agents.

Although, we did not make an attempt to study the differences in the cost of pre-marketing development of new drugs in different therapeutic categories, we postulate that the observed differences in drug-treatment cost, and subsequently the drug sales revenue, may play a role in the decision making process for the introduction of new drugs. It may also be one of the factors that has led to a relative shortage of new antibiotics. It should be emphasized that the pre-marketing cost of development of new chemical entities has been found to be higher for anti-infective agents compared to several other categories of drugs, including cardiovascular and neuro-pharmacological agents [1].

Our study has several limitations. First, we had to measure the drug cost of a defined period of treatment (ten-day treatment) in order to provide some comparative estimates of treatment cost with new drugs in different therapeutic categories. The selection of any time period (e.g. one-day, one-week, one-month, etc) for our comparative analysis would have its own advantages and disadvantages given that the duration of treatment differs considerably for the numerous acute, sub-acute, and chronic diseases. Second, we calculated only the drug-treatment cost without taking into consideration other important factors that influence the cost of medical care, including cost related to the administration of parenteral medications. Third, we did not take into account data about the effectiveness and safety of new drugs in order to perform a comparative assessment of the cost-effectiveness of new agents in different therapeutic categories.

In addition, we did not examine the reasons for the considerable differences in the drug-treatment cost of with newly approved agents. Several factors may contribute to the observed differences in the cost; including the cost of development, production, and introduction of new drugs into the clinical practice [13]. Specifically, the cost of the infrastructure necessary for the development of new drugs may differ for different therapeutic categories. Furthermore, the cost of clinical trials, required for the approval of new drugs, may be also be different for the various therapeutic categories [14], [15]. For example, a longer follow up period of observation is necessary for the determination of the outcome in clinical trials studying anti-neoplastic compared to antibacterial agents. Moreover, differences in the failure rate of new drugs to successfully complete phases I to IV of clinical trials, may contribute to the increased cost of production of new anti-neoplastic and immunosuppressive drugs.