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Starting a pharmacokinetic dosing service.

New microcomputer programs and economical drug monitoring tests have enabled many more hospitals to fine-tune drug doses.

Special chemistry has just processed another batch of drug monitoring specimens, and there still are as many toxic and subtherapeutic levels as therapeutic levels. The doctors keep blaming the laboratory for these unusual results, but the controls and instruments check out fine.

Lab personnel wonder if the nurses administered the medicine at the right time; the nurses wonder if the pharmacist dispensed the proper dose; and the pharmacist wonders if the lab knows how to perform the test. And everyone wonders how doctors can regulate therapy with so much potential for error.

What's the solution to all this therapeutic drug monitoring confusion? It may be time for the laboratory to start a pharmacokinetic dosing service. That once may have been considered farfetched at community hospitals, but such services are now spreading out from their traditional place in large university medical centers.

The current growth of pharmacokinetic dosing is due to the recent availability of microcomputers able to handle mathematically complex kinetic programs and to improvements in TDM that have resulted in rapid, relatively inexpensive drug level testing. That dosing services can improve therapy and help shorten hospital stays hasn't been overlooked by alert laboratorians and administrators, either.

A successful dosing service has two vital components-a computer system and a team of dedicated individuals. The first component comes in a wide range of complexity and prices. Fifty or more computer programs are now available for TDM services. A small system can consist of only a programmable calculator and a free program copied from medical or pharmaceutical journals. A medium-size system uses a 64-256K microcomputer coupled with an appropriate algorithm. The largest system may include a computer with hard disk capability, printers, and thousands of dollars' worth of software.

If your laboratory already has access to a standard 64-256K microcomputer, such as an Apple 11 or IBM PC, all you need to test the pharmacokinetic waters is a dosing program. A list of programs, some ranging as low as $100 to $600, can be found in the April 1986 issue of MLO.

Although a dependable computer system is important, the second component of a smoothly running dosing service-its human element-is more critical. Once the team is selected, the areas of responsibility for members must be delineated, and their activities have to be coordinated into a smoothly working system, a key part of which is a daily meeting. One of the team's first jobs is to design formats for report forms.

The dosing team often consists of a pharmacist, one or more representatives from the laboratory (commonly from microbiology or chemistry), a nurse, and a physician, who on some teams is a pathologist. After the team discusses the results and receives any further input from the team doctor, the patient's physician is contacted with the recommended dosage changes, if any have been found necessary.

The individual team members bring unique skills and insights to the dosing service. For example, the nursing member insures prompt and proper administration of medication, notifies the laboratory of the precise time for specimen collection, and provides the patient data needed to recommend an initial dose to the attending physician.

The pharmacist contributes information on cost-effective drug dosage, on frequency of administration, and on other drugs that may interact with the drug in question. The laboratory is responsible for timely, accurate therapeutic drug monitoring determinations and may provide ancillary information, suchas the minimum inhibitory concentration of an aminoglycoside antibiotic. The entire team usually meets at the computer workstation to update information on patients before the common early afternoon changeover of IV bags.

Let's examine how a dosing service operates. Suppose a 61-year-old woman hospitalized for bacterial pneumonia begins a standard intravenous gentamicin dose of 60 mg every eight hours. Three days later, her pneumonia worsens, and the physician asks the dosing service to recommend a new dosage. The service swings into action and collects specimens at different times for peak and trough concentrations of gentamicin, beginning with the next dose.

Peak and trough values of 3.9 Kg/ml and 2. 1 Kg/ml are returned by the laboratory. The dosing team next consults the computer by entering the name of the drug, the dosage, the site of infection, and measured levels, along with such patient data as gender, age, height, weight, and serum creatinine level.

The program calculates the patient's volume of drug distribution, creatinine clearance, and elimination rate constant. It also reminds the team that optimal gentamicin therapy for pneumonia usually requires serum peaks that are above 6 Kg/ml and troughs below 2 Kg/ml.

As shown in Figure 1, the program then gives three choices of new dosage (with predicted peaks/troughs): 150 mg gentamicin every 14 hours (6.6/1.7), 160 mg every 16 hours (6.6/1.4), or 160 mg every 18 hours (6.3/ 1.1).

The pharmacist recommends a 160 mg dose, since gentamicin comes prepackaged in cost-saving units of 80 mg. That still leaves the interval of administration open: 16 or 18 hours. The nurse on the team supports the former because it fits in with the hospital's routine times for medication, every eight hours.

These suggestions are then passed on to the physician for ordering. The computer also alerts the dosing team that the physician should order a repeat creatinine and urinalysis. Gentamicin is considered very nephrotoxic, and rising creatinine levels or abnormal urine results could signal kidney damage. The computer recommends another peak/trough concentration measurement in three days to verify that the dose has been appropriate.

By the time the laboratory reports the next peak and trough concentrations-6.9 Kg/ml and 1.5 Kg/ml, respectively-the patient's fever is already down, and she is rapidly improving.

This example illustrates how the team's members, using their individual skills, successfully interact. A computerized pharmacokinetic dosing service can optimize patient care in the least expensive, most efficient manner. Such a service may be just what your hospital needs to put a "byte" into TDM.

1. Baer, D.M. Tips on Technology. MLO 18(4):11-14, April 1986

The author is pathologist at Palms of Pasadena Hospital in South Pasadena/St. Petersburg, Fla
COPYRIGHT 1987 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1987 Gale, Cengage Learning. All rights reserved.

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Author:Barton, Thomas K.
Publication:Medical Laboratory Observer
Date:Nov 1, 1987
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