Elevated serum creatinine levels in three patients treated with phenacemide

A rise in plasma creatinine that is not a sign of renal failure: which drugs can be responsible?

This is a review of the available information about drugs which cause an increase in plasma creatinine concentration without decreasing glomerular filtration rate (GFR). The GFR is the main, but not the single, determinant of the plasma creatinine levels. Several drugs, such as cimetidine, trimethoprim, corticosteroids, pyrimethamine, phenacemide, salicylates and active vitamin D metabolites, have been reported to increase plasma creatinine without influencing its glomerular filtration. Cimetidine, trimethoprim, pyrimethamine and salicylates can inhibit secretion of creatinine by the proximal tubule. Corticosteroids and vitamin D metabolites probably modify the production rate and the release of creatinine. The exact mechanism of phenacemide-creatinine interaction is not fully explained. These drug-induced alterations in plasma creatinine concentration have clinical significance when GFR is estimated by using plasma creatinine.

Creatinine metabolism impairment by an anticonvulsant drug, phenacemide

OBJECTIVE

To report two cases of increased true serum creatinine (Scr) without renal failure caused by an anticonvulsant drug, phenacemide, and to discuss the possible mechanisms.

CASE SUMMARY

Two patients treated with phenacemide were investigated for markedly increased Scr and decreased creatinine clearance (Clcr) values. Glomerular filtration rates, as determined by 125I-iothalamate clearance, were normal in both patients and analytical interferences with the Jaffé reaction were excluded. After discontinuation of the drug, phenacemide concentrations became undetectable within 2 days but it took 7-14 days for Scr and Clcr to return to normal values.

DISCUSSION

The Scr increase with phenacemide (120-170 percent) was higher than that reported with cimetidine or trimethoprim (10-40 percent) and could not be explained solely by inhibition of the tubular secretion of creatinine. The hypothesis of an overproduction of creatinine caused by phenacemide was ruled out by experimental studies in rats. Creatinine increase in tissues was lower than that in the serum of rats given phenacemide. In vitro creatinine influx into red blood cells was inhibited in a dose-dependent way by phenacemide.

CONCLUSIONS

Increased Scr concentrations in these patients could be related to an inhibition of transport and a decrease in creatinine volume of distribution. Creatinine concentrations should not be considered when dosage adjustments of renally eliminated drugs are being calculated for patients with such metabolic interferences.

Drug-induced alterations in serum creatinine concentrations

OBJECTIVE

To provide a comprehensive review of drug-induced alterations in serum creatinine concentrations (SCrs).

DATA SOURCES

Information was obtained from a MEDLINE search, reference lists from articles identified in the search, review articles, and abstracts.

STUDY SELECTION

Emphasis was placed on clinical studies of direct relevance to clinical practitioners.

DATA EXTRACTION

Literature was assessed for its methodology, results, discussion, and conclusion.

DATA SYNTHESIS

Two analytical systems to assay SCr are commonly employed in clinical practice--the Jaffé-based and enzymatic methods. Several drugs have been reported to interfere with SCr results obtained with both analytical systems by producing assay interference. In addition, trimethoprim, cimetidine, and salicylates produce elevations in the SCr by altering the normal elimination pathways of creatinine. Phenacemide has been reported to increase creatinine elimination, but the mechanism of this effect is unknown.

CONCLUSIONS

Pharmacists should recognize the clinical significance of drug-induced interference with SCr and propose alternative methods of determining concentrations in selected patients.

Using estimated creatinine clearance for individualizing drug therapy: a reassessment

Estimates of renal function are frequently used to design individual dosing regimens. The accuracy of these estimates naturally influences their ability to predict certain pharmacokinetic parameters and appropriate drug dosages. Creatinine clearance is the most widely used estimate of renal function. Many formulas have been developed to provide a quick, relatively accurate prediction of creatinine clearance and, supposedly, the glomerular filtration rate (GFR). However, an understanding of the limitations associated with creatinine clearance estimations raises questions concerning their reliability as an aid in individualizing drug therapy. Many factors such as disease states, age, diet, analytical variations, and drug interactions affect the relationship between estimates and measures of creatinine clearance and GFR. As a result, creatinine clearance estimates using these formulas are often poor reflections of measured creatinine clearance or GFR. Also, studies comparing measured creatinine clearance with more accurate methods of assessing renal function (i.e., inulin) reveal errors that are often exaggerated as renal function declines. Therefore, estimated creatinine clearance is twice removed from the associated pharmacokinetic parameter. Despite these limitations, no other clinically relevant and convenient assessment of renal function is available. The authors recommend that the appropriate caveats be considered when using these tools clinically. For drugs with narrow therapeutic indices, estimates of creatinine clearance should only be used to establish initial dosing regimens, with subsequent therapy based on parameters generated from concentration determinations.