Background : The purpose of this study was to develop, implement and evaluate the pharmacist intervention program designed to identify and correctly adjust the dosage of $H_2$-receptor antagonists ($H_2RA$) in renally impaired patients and promote timely conversion of $H_2RA$ from IV to PO therapy. Methods : The study population consisted of renally impaired patients who received $H_2RA$ therapy from April 9 to May 8, 2001 at Hallym Medical Center. Each morning a specifically developed software program identified patients with serum creatinine (Scr) greater than 1.2 mg/dl or age greater than 65 years. The pharmacist, then screened the pharmacy profiles of the identified patients to determine if the patient was on $H_2RA$. For these patients on $H_2RA$ with renal impairement the creatinine clearance (CrCl) was calculated using Cockroft & Gault equation. The pharmacist determined the proper dosage for each identified patients based on the calculated CrCl and the oral dosage that would be appropriate for whom IV therapy was no longer indicated. Result : A total of 149 cases (101 patients) were monitored during the study period. The dosage was inappropriately prescribed for renal function in 61 of 149 cases (41%), and of those, pharmacist made recommendations for 58 cases of which 33 cases (57%) were accepted by the physicians. The administration route of H2RA was inappropriately used as IV in 22 of 53 cases (42%), and pharmacist made recommendations for those 22 cases of which 15 cases (68%) were accepted. Conclusion : Monitoring of patients with renal dysfunction by a pharmacist improved the dosing of $H_2RA$ and a dosing program of patients with renal impairment would be of benefit to other clinicians and institutions seeking to optimize patient care.