Printer Friendly

Monitoring drug therapy via clinical laboratory tests.

Monitoring drug therapy via clinical laboratory tests

Monitoring drug levels has in recent years become a significant tool in the safe maintenance of patients on long-term drug therapy. Repeated studies indicate, however, that inadequate or excessive drug dosages are not uncommon with or without serum drug levels. Therefore, laboratory tests other than drug concentration measurements are also needed.

A number of drugs produce abnormal findings in the blood and/or urine. This may reflect direct toxicity or adverse pharmacologic reaction with other drugs. Many such reactions occur idiosyncratically and may be difficult to predict. Often, such reactions occur when drug levels are within the recommended therapeutic range.

In many instances, serum drug levels are unavailable, such as for antihypertensive diuretics, methyldopa, many cardiac agents, anticoagulants, H.sub.2 inhibitors, thyroid replacements, oral contraceptives, and estrogen therapy. Even in cases where drug assays are available, adverse reactions may be complicated by the presence of active and potentially toxic/active metabolites. Such is the case with procainamide where the full effect of the drug cannot be assessed without measuring for its metabolite N-acetyl procainamide.

Pharmaceutical companies have long recognized the necessity of periodic monitoring of electrolyte status, renal functioon, bone marrow, and hepatic function in connection with certain therapeutic regimens. A failure to follow these pharmaceutical guidelines may lead to serious or life-threatening situations, as in the case of a patient receiving diuretics who is seen in the emergency room with a potassium level of 2.0 mEq/L or a patient on long-term lithium therapy presenting with renal failure. Such situations could and should be avoided by adherence to proper schedules of periodic laboratory testing and monitoring of critical analytes.

Table I provides the clinician and the clinical laboratory with a ready reference to laboratory tests, other than actual serum drug levels, that can be used to minimize adverse drug reaction--both exaggerated primary effects, such as hemorrhaging in a patient on warfarin, and side effects, such as hepatic failure or thrombocytopenia in a patient on valproic acid. The medications in Table I are commonly used in outpatient settings and frequently require long-term administration. Drug levels are routinely ordered for a number of them on an outpatient basis.

The suggested frequency for laboratory tests used to monitor the safety of these drugs is based upon experience and published data. The decision to modify therapy should be based upon clinical necessity and interpretation, rather than a reflex response to an individual laboratory value, but the use of a regular testing schedule will often alert the clinician to possible impending toxic side effects.

If an untoward effect does develop, it is up to the clinician to assess the benefits/risk ratio and determine whether the therapy should be continue. Examples of such untoward effects are a positive Coombs test for a patient on methyldopa or a positive ANA for a patient on procainamide therapy.

In some instances, laboratory tests are needed to establish maintenance dosage, such as T.sub.4 and TSH for determining euthyroid status in patients on thyroid replacement therapy.

Modifications in the suggested schedule may be needed based upon results of therapeutic drug levels and clinical judgment. Additional information may be found in the specific references cited below.
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.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:reference table for tests, other than actual drug levels, that monitor drug therapy
Author:Assarian, Gary S.; Fitter, William M.
Publication:Medical Laboratory Observer
Date:Mar 1, 1987
Previous Article:Could your lab deal with a nuclear accident?
Next Article:Quality control in the new environment: lab testing near the patient.

Related Articles
A lab-pharmacy push to cut drug therapy costs.
Quality control in the new environment: ligand assay and TDM; part II.
The lab's role in cholesterol management.
Future challenges for the clinical immunology laboratory.
Clinical trials: a golden opportunity for laboratories?
Clinical trials: A golden opportunity for laboratories?
Nevirapine (VIRAMUNE [R]) Strengthens Warning on Liver, Skin Toxicities.
The role of esoteric reference laboratory as a partner for growth.
Point-of-care testing in oral anticoagulation: what is the point?

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters