Radioimmunoassay for the Synthetic Ergoline Derivative Cabergoline in Biological Fluids

A fatal overdose of the ergot derivative cabergoline

A 79-year-old woman, with Parkinson's disease treated with cabergoline, was admitted to a hospital due to jaundice and weakness. She was found confused, absent minded, and died after 2 weeks. Autopsy showed an extrahepatic bile duct adenocarcinoma with spread to the gall bladder, the liver, and regional lymphnodes. While cleaning the hospital bed after her death, the nurses found several tablets hidden in the bed. Biological samples obtained at the autopsy were screened for common drugs and narcotics. Several drugs such as buprenorphine, codeine, paracetamol, and propranolol were detected in the blood at therapeutic levels. A method to determine cabergoline in whole blood and other forensic matrices was developed, and further investigations determined cabergoline concentrations in whole blood and liver tissue of 94 and 3100 microg/kg, respectively. The blood concentration was 100 times above the therapeutic level reported on cabergoline in plasma and in combination with her symptoms, suggest she took a fatal overdose of cabergoline.

Clinical pharmacokinetics of cabergoline

Cabergoline is a synthetic ergoline dopamine agonist with a high affinity for D(2) receptors indicated for use in both early and advanced Parkinson's disease and in hyperprolactinaemic disorders. Following oral administration, peak plasma concentrations of cabergoline are reached within 2-3 hours. Over the 0.5-7mg dose range, cabergoline shows linear pharmacokinetics in healthy adult volunteers and parkinsonian patients. Cabergoline is moderately bound (around 40%) to human plasma proteins in a concentration-independent manner; concomitant administration of highly protein-bound drugs is unlikely to affect its disposition. The absolute bioavailability of cabergoline is unknown. Cabergoline is extensively metabolised by the liver, predominantly via hydrolysis of the acylurea bond of the urea moiety. Cytochrome P450-mediated metabolism appears to be minimal. The major metabolites identified thus far do not contribute to the therapeutic effect of cabergoline. A significant fraction of the administered dose undergoes a first-pass effect. Less than 4% is excreted unchanged in the urine. The elimination half-life of cabergoline estimated from urinary data of healthy subjects ranges between 63 and 109 hours. Mild to moderate renal and hepatic impairment, administration of food and the use of concomitant antiparkinsonian medications, such as levodopa and selegiline, have no effect on the pharmacokinetics of cabergoline.The pharmacokinetic properties of cabergoline allow once daily administration in patients with Parkinson's disease and twice weekly administration in patients with hyperprolactinaemia, making this drug advantageous over other dopaminergic agents in term of both therapeutic compliance and better symptom control.

High-sensitivity quantitation of cabergoline and pergolide using a triple-quadrupole mass spectrometer with enhanced mass-resolution capabilities

Quantitative analysis of pharmaceuticals with low systemic plasma levels requires the utmost in sensitivity and selectivity from the analytical method used. A recently introduced triple-quadrupole mass spectrometer with unique enhanced mass-resolution capability was evaluated in the analysis of two such drugs, cabergoline and pergolide, in plasma. Liquid chromatographic/electrospray ionization selected reaction monitoring determination of cabergoline in plasma at unit mass-resolution demonstrated improved sensitivity (50 fg on-column), coupled with suitable accuracy and precision over a broad linear dynamic range covering five orders of magnitude (50 fg to 5 ng on-column). Liquid chromatographic/atmospheric pressure chemical ionization selective reaction monitoring determination of pergolide in plasma also attained a high level of sensitivity (500 fg on-column) at unit mass-resolution, with accuracy and precision values well within pharmaceutical industry standards. Again, a linear dynamic range covering five orders of magnitude (500 fg to 50 ng on-column) was achieved for the assay. Utility of the enhanced mass-resolution feature of the triple-quadrupole mass spectrometer in the determination of pergolide resulted in an improvement in analyte sensitivity (250 fg on-column) and linear dynamic range (250 fg to 50 ng on-column).

Cabergoline

Cabergoline (CAB) (1-[(6-allelylergolin-8 beta-yl)carbonyl]-1-[3-(dimethylamino)propyl]-3-ethyl-urea) is an ergoline derivative with potent, selective and long-lasting inhibitory activity on prolactin (PRL) secretion acting on dopamine receptors present in pituitary lactotrophes. Receptor binding studies have demonstrated that CAB has high in vitro selectivity and affinity for the subtype D2 of the dopamine receptor. In cultures of rat anterior pituitary cells, the concentrations of CAB and bromocriptine required to inhibit PRL secretory activity by 50% (IC50) were 0.1 and 3.4 nmol/l, respectively. As compared to bromocriptine, CAB was more potent in inhibiting the binding of [3H]N-n-propylnorapomorphine and it occupied the receptor for longer. These effects were observed in all areas of the rat brain. In vivo, CAB at doses of 0.125-1 mg twice weekly caused a dose-dependent suppression of PRL secretion in women with hyperprolactinaemia. CAB was shown to be significantly more effective than bromocriptine in inducing a complete biochemical response and clinical efficacy and was better tolerated than bromocriptine in the majority of patients. Notable tumour shrinkage until tumour disappearance was observed during CAB treatment in most patients with macroprolactinoma. CAB was also shown to be effective in patients resistant or poorly responsive to bromocriptine. In view of the limited data on CAB-associated pregnancies and the long half-life of the drug, it is currently recommended that women seeking to became pregnant, once ovulatory cycles have been established, should discontinue CAB therapy 1 month before they intend to conceive. However, no data on negative effects on pregnancy or offspring have been reported. The great efficacy of CAB together with its excellent tolerability makes this drug the current treatment of choice for the majority of patients with hyperprolactinaemic disorders. Very recently, the efficacy of CAB treatment has been reported in patients with acromegaly and clinically non-functioning adenomas with controversial results. CAB was also reported to have some efficacy in patients with Nelson's syndrome and Cushing's disease although these data are available only for limited case reports.

Determination of FCE 23884, a new ergolene derivative, and its possible metabolite, the 6-nor-derivative in plasma by high-performance liquid chromatography with fluorescence detection

A sensitive and selective high-performance liquid chromatographic method for the determination of FCE 23884 and its 6-nor-derivative (FCE 26506) in plasma has been developed. After buffering the plasma samples, the compounds and the internal standard were extracted with ethyl ether-n-octanol (9:1, v/v), back-extracted into 0.01 M phosphoric acid and then analysed by reversed-phase liquid chromatography. Quantification was achieved by fluorescence detection of the eluate. The linearity, precision and accuracy of the method were evaluated. No interference from the biological matrix was observed. The assay was adequate for the quantification of plasma levels of the two compounds after a single oral dose of 1 mg of FCE 23884 in humans.