LETTERS
Hj-antagonist dosing in the elderly based on renal function
TOTIlEEDITOR: The age-relateddecline in renal function indicates that many geriatric patients have mild to moderate renal insufficiency.' The dosage, dosage interval,or both of renally eliminated medications, such as ranitidineand cimetidine,can be adjusted without compromisingefficacy (serum concentrations) when a patient has renal impairment.' Although guidelines for dosage adjustment in patients with renal insufficiency are available, they are not commonly applied in clinical practice. Renal impairment predisposes geriatric patients to central nervous system (CNS) toxicity from histamine Hj-antagorusts. Dosage adjustment would increase the safety margin in this regard. We chose to study the impactof renal function-based dosing of parenteralranitidineand cimetidine in our hospitalized geriatric population. Such dosage adjustment lends itself to continued efficacy, a greater margin of safety for patients, and economic benefitsfor the institution. During a 16-month period, parenteral cimetidine and ranitidine regimens for patients aged 62 years and older were evaluated by pharmacists. Renal function for each patient taking an Hj-antagonistwas evaluated by measured creatinine clearance or calculated creatinine clearance using the Cockcroftand Gault formula.' Pharmacistsrecommendeda change in Hj-antagonistdosing intervals based on renal function from modified literature guidelines (Table 1).3,. The final recommendation included consideration of the patient's clinical condition via chart review and/or communication with the physician. A recommendation was entered in the progress notes by pharmacists with suggested dosing alterations. Dosage adjustments were not recommended for patients with pancreatitisor active gastrointestinal bleeding, per agreementwith staff gastroenterologists. The patient data collected included Hj-antagonist, dosing regimen, age, height,weight,and serum creatinineconcentration. The costs recorded were those of the drugs and piggyback bags saved with intervention. Monthlycomputerizedspreadsheets were programmedto calculate creatinineclearanceor incorporate the measuredvalue, when available. Daily cost avoidancewas calculatedby multiplyingthe cost items by the number of doses saved per day. During the study period, 326 courses of Hj-antagonist therapy were monitored. The average age of the study population was 70.7 years (range 62-96). Pharmacists were responsible for altering 74 courses of therapy,resulting in $1728.48cost avoidance. This represented 10.3percent of the total expenditures for parenteral Hj-anragonists during the study. Pharmacist interventions not accepted were 61 for a total of 135 potential intervention courses. The reasons offered for interventionsnot acceptedincludedthe physicianoverlookingthe pharmacist's note or disagreeing with the suggesteddosing alteration.No documented therapeutic failures attributableto dosage alteration were observed. Additionally, no CNS toxicityor other toxicitieswere noted during the study period. Private sector hospitals may view this approach as undesirable because of a loss of charges. However, when consideringthis age group, to which the interventions typically will be applied, it becomes apparent Table I. RecommendedHj-Antagonist Dosage IntervalChanges CREATININE CLEARANCE VALUES (mL/min) DRUG
>60
30--60
Hj-antagonist dosing in the elderly based on renal function
TOTIlEEDITOR: The age-relateddecline in renal function indicates that many geriatric patients have mild to moderate renal insufficiency.' The dosage, dosage interval,or both of renally eliminated medications, such as ranitidineand cimetidine,can be adjusted without compromisingefficacy (serum concentrations) when a patient has renal impairment.' Although guidelines for dosage adjustment in patients with renal insufficiency are available, they are not commonly applied in clinical practice. Renal impairment predisposes geriatric patients to central nervous system (CNS) toxicity from histamine Hj-antagorusts. Dosage adjustment would increase the safety margin in this regard. We chose to study the impactof renal function-based dosing of parenteralranitidineand cimetidine in our hospitalized geriatric population. Such dosage adjustment lends itself to continued efficacy, a greater margin of safety for patients, and economic benefitsfor the institution. During a 16-month period, parenteral cimetidine and ranitidine regimens for patients aged 62 years and older were evaluated by pharmacists. Renal function for each patient taking an Hj-antagonistwas evaluated by measured creatinine clearance or calculated creatinine clearance using the Cockcroftand Gault formula.' Pharmacistsrecommendeda change in Hj-antagonistdosing intervals based on renal function from modified literature guidelines (Table 1).3,. The final recommendation included consideration of the patient's clinical condition via chart review and/or communication with the physician. A recommendation was entered in the progress notes by pharmacists with suggested dosing alterations. Dosage adjustments were not recommended for patients with pancreatitisor active gastrointestinal bleeding, per agreementwith staff gastroenterologists. The patient data collected included Hj-antagonist, dosing regimen, age, height,weight,and serum creatinineconcentration. The costs recorded were those of the drugs and piggyback bags saved with intervention. Monthlycomputerizedspreadsheets were programmedto calculate creatinineclearanceor incorporate the measuredvalue, when available. Daily cost avoidancewas calculatedby multiplyingthe cost items by the number of doses saved per day. During the study period, 326 courses of Hj-antagonist therapy were monitored. The average age of the study population was 70.7 years (range 62-96). Pharmacists were responsible for altering 74 courses of therapy,resulting in $1728.48cost avoidance. This represented 10.3percent of the total expenditures for parenteral Hj-anragonists during the study. Pharmacist interventions not accepted were 61 for a total of 135 potential intervention courses. The reasons offered for interventionsnot acceptedincludedthe physicianoverlookingthe pharmacist's note or disagreeing with the suggesteddosing alteration.No documented therapeutic failures attributableto dosage alteration were observed. Additionally, no CNS toxicityor other toxicitieswere noted during the study period. Private sector hospitals may view this approach as undesirable because of a loss of charges. However, when consideringthis age group, to which the interventions typically will be applied, it becomes apparent Table I. RecommendedHj-Antagonist Dosage IntervalChanges CREATININE CLEARANCE VALUES (mL/min) DRUG
>60
30--60
