Simultaneous analysis of digitoxin and its clinically relevant metabolites using high-performance liquid chromatography and radioimmunoassay

Measurement of serum digitoxin in patients by radioimmunoassay using specific antiserum

INTRODUCTION

Digitoxin is used to treat patients with heart failure.

METHODS

A radioimmunoassay procedure for the specific determination for digitoxin in serum was developed using the antiserum (antiserum (A)) raised against digitoxin 3'-hemisuccinate-BSA conjugate.

RESULTS

The intra- and interassay variability were <10% in the range of 5-100 ng/ml. The specificities of antiserum (A) and the commercial anti-digitoxin antiserum (antiserum (B)) were assessed by cross-reactivity studies with various related compounds. Antiserum (A) was highly specific for digitoxin. Mean digitoxin concentrations in serum samples (n=34) from digitalized patients by RIA using these antisera were 10.0 and 12.4 ng/ml, respectively.

CONCLUSION

This RIA using antiserum (A) measure unmetabolized digitoxin and may be applicable for pharmacokinetic studies.

High-performance liquid chromatography-ionspray mass spectrometry for the specific determination of digoxin and some related cardiac glycosides in human plasma

An original method based upon high-performance liquid chromatography coupled to ionspray mass spectrometry (HPLC-ISP-MS) has been developed for the identification and quantification in plasma of several cardiac glycosides, namely digoxin, digitoxin, lanatoside C and acetyldigitoxin. After single-step liquid-liquid extraction by chloroform-2-propanol (95:5, v/v) at pH 9.5 using oleandrin as an internal standard, solutes are separated on a 4 microm NovaPak C18 (Waters) column (150x2.0 mm, I.D.), using a gradient of acetonitrile-2 mM NH4COOH, pH 3 buffer (flow-rate 200 microl/min, post-column split 1:3). Detection is done by a Perkin-Elmer Sciex API-100 mass analyzer equipped with an ISP interface. In most instances the major ion observed is not [M+H]+ as expected, but [M+NH4]+. The mean retention times (min) are: lanatoside C, 5.74; digoxin, 6.00; digitoxin, 8.08, oleandrin, 8.30, acetyldigitoxin, 8.66 and 9.01 (isomers alpha and beta, respectively). The lower limits of detection in single ion monitoring mode range from 0.15 ng/ml (alpha- and beta-acetyldigitoxin) to 0.60 ng/ml (lanatoside C), making the method less sensitive than radioimmunoassay, whereas it is much more specific.

Digitoxin and its metabolites in patients with liver cirrhosis

Pharmacokinetic profile and urinary excretion of digitoxin and 4 metabolites were investigated in 9 patients with biopsy confirmed liver cirrhosis (median antipyrine clearance 20.0 +/- 5.4 ml/min; X +/- SEM) and were compared with that of 8 healthy volunteers (antipyrine clearance 36.9 +/- 4.9 ml/min) following intravenous and p.o. administration of 1 mg digitoxin. The kinetic parameters derived from the digotoxin plasma concentration time curve and from urinary recovery including total clearance of unchanged digitoxin did not differ significantly between both groups investigated. Renal clearance of digitoxin was 0.017 +/- 0.005 ml/min/kg in the patient group and 0.011 +/- 0.002 ml/min/kg in the volunteers (NS); it was 0.00340 +/- 0.00047 ml/min/kg and 0.00223 +/- 0.00039 ml/min/kg, respectively for digitoxigenin-bis-digitoxoside (NS), 0.00006 +/- 0.00001 ml/min/kg and 0.00016 +/- 0.00005 ml/min/kg for digitoxigenin-mono-digitoxoside (P < 0.05), 0.00041 +/- 0.00013 ml/min/kg and 0.00088 +/- 0.00032 ml/min/kg for digitoxigenin (P < 0.05), 0.00135 +/- 0.00049 ml/min/kg and 0.00113 +/- 0.00042 ml/min/kg for digoxin (NS). In conclusion, hydrolysis of digitoxin is altered in liver cirrhosis, whereby a significant reduction in the renal clearance and urinary recovery of digitoxigenin-mono-digitoxoside and digitoxigenin was seen in the present study.

Chromatography of cardiac glycosides

Most of the recently reported methods for the quantitation of cardiac glycosides have been for digoxin and its metabolites. Recent procedures using high-performance liquid chromatography-radioimmunoassay (HPLC-RIA) and HPLC following derivatization show appreciable improvements in accuracy and specificity for quantitating digoxin in the low nanogram range. Gas chromatographic procedures have been explored to a very limited extent and further advances in the quantitation of cardiac glycosides are anticipated to arise from the use of laser desorption-Fourier transform mass spectrometry. However, currently, HPLC with derivatization and HPLC-RIA techniques remain the techniques of choice for quantitation of digoxin and/or its metabolites based on considerations of ease of use, sensitivity, specificity, accuracy and reproducibility.