Inappropriate use of antibiotics needlessly increases drug expenditures, enhances the emergence of antimicrobial resistance in hospitals and heightens the risk of toxicity, especially in elderly patients. This population is very sensitive to inappropriate drug treatment because of pharmacological and pharmacokinetic changes, reduced homeostatic functional reserve, multiple underlying diseases (e.g. renal failure) and polypharmacy (leading to drug interactions and side effects). To assess antibiotic prescription in a geriatric university hospital with a restrictive drug formulary, we analyzed data extracted from the Drug Kardex (a standardized synthesis of all prescribed medicines) during 4 cross-sectional drug utilization studies, carried out in 1996 on all hospitalized patients. RESULTS: 1138 patients' Kardex have been analyzed. 20% of these patients received one or more antibiotic treatments. In total 268 antibiotic treatments (AB) were prescribed, 84 in March, 44 in June, 71 in September and 66 in December. 21 different AB were used, the five most frequently prescribed AB being amoxycillin-clavulanic acid, ceftriaxone, ciprofloxacin, metronidazole, co-trimoxazole and representing 69% of all AB. Most of the AB were given in an oral form (63%) and in one standard dose. Dose adjustments in these very old patients with a high percentage of renal failure were apparently rarely done. The choice of rather broad spectrum AB may be due to the fact that obtaining an appropriate bacteriological culture from elderly patients with respiratory tract infections is difficult, but was also due to a lack of diagnostic subcategorization of the infection. Undesirable effects of the restrictive drug formulary were also noted: large utilization of ciprofloxacine (only fluoroquinolone on the hospital's drug list) for urinary tract infections instead of other more appropriate antibiotics. CONCLUSION: It is important to individualize antibiotic drug therapy with respect to underlying diseases, site of infection and antibiotic sensitivity patterns, especially in elderly patients. Restrictive hospital drug formularies are not sufficient to assure rational drug use, but should be associated with broader educative measures.