UPLC-MS/MS determination of phentolamine in human plasma and its application to a pharmacokinetic study.

A sensitive and rapid ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed to determine phentolamine in human plasma. Sample preparation was accomplished through a simple liquid-liquid extraction with ethyl acetate. Chromatographic separation was carried out on an Acquity UPLC BEH C18 column using an isocratic mobile phase system composed of acetonitrile and 1% formic acid in water (33:67, v/v) at a flow rate of 0.45 mL/min. Mass spectrometric analysis was performed using a QTrap5500 mass spectrometer coupled with an electro-spray ionization (ESI) source in the positive ion mode. The MRM transitions of m/z 282.1 → 212.0 and m/z 237.1 → 194.2 were used to quantify for phentolamine and carbamazepine (internal standard, IS), respectively. The linearity of this method was found to be within the concentration range of 0.5-100.0 ng/mL with a lower limit of quantification of 0.5 ng/mL. Only 1.0 min was needed for an analytical run. This fully validated method was successfully applied to the pharmacokinetic study after oral administration of 60 mg phentolamine to 20 Chinese healthy male volunteers.

Pharmacokinetics of lidocaine with epinephrine following local anesthesia reversal with phentolamine mesylate.

Phentolamine mesylate accelerates recovery from oral soft tissue anesthesia in patients who have received local anesthetic injections containing a vasoconstrictor. The proposed mechanism is that phentolamine, an alpha-adrenergic antagonist, blocks the vasoconstriction associated with the epinephrine used in dental anesthetic formulations, thus enhancing the systemic absorption of the local anesthetic from the injection site. Assessments of the pharmacokinetics of lidocaine and phentolamine, and the impact of phentolamine on the pharmacokinetics of lidocaine with epinephrine were performed to characterize this potentially valuable strategy. The blood levels of phentolamine were determined following its administration intraorally and intravenously. Additionally, the effects of phentolamine mesylate on the pharmacokinetics of intraoral injections of lidocaine with epinephrine were evaluated. Sixteen subjects were enrolled in this phase 1 trial, each receiving 4 drug treatments: 1 cartridge lidocaine/epinephrine followed after 30 minutes by 1 cartridge phentolamine (1L1P), 1 cartridge phentolamine administered intravenously (1Piv), 4 cartridges lidocaine/epinephrine followed after 30 minutes by 2 cartridges phentolamine (4L2P), and 4 cartridges lidocaine/epinephrine followed by no phentolamine (4L). Pharmacokinetic parameters estimated for phentolamine, lidocaine, and epinephrine included peak plasma concentration (Cmax), time to peak plasma concentration (Tmax), area under the plasma concentration-time curve from 0 to the last time point (AUClast) or from time 0 to infinity (AUCinf), elimination half-life (t1/2), clearance (CL), and volume of distribution (Vd). The phentolamine Tmax occurred earlier following the intravenous administration of 1Piv (7 minutes than following its submucosal administration in treatment 1L1P (15 minutes) or 4L2P (11 minutes). The phentolamine t1/2, CL, and Vd values were similar for 1L1P, 1Piv, and 4L2P. The Tmax for lidocaine occurred later and the Cmax for lidocaine was slightly higher when comparing the 4L2P treatment and the 4L treatment. The phentolamine-induced delay of the lidocaine Tmax likely represents phentolamine's ability to accelerate the systemic absorption of lidocaine from oral tissues into the systemic circulation.

Flow-injection chemiluminescence determination of phentolamine based on its enhancing effect on the luminol-potassium ferricyanide system.

It was found that the light emission produced by the oxidation of luminol by potassium ferricyanide in the basic medium was enhanced by phentolamine, a drug recently used to treatment of male and female sexual dysfunction. The optimum conditions for this chemiluminescent reaction were studied in detail by a flow-injection system. A new, simple and rapid method has been developed under the optimum conditions for determination of phentolamine. This method has the advantages of high sensitivity, good reproducibility and low detection limit. On the basis of investigation of chemiluminescent, fluorescent and UV spectra of phentolamine in basic solution containing potassium ferricyanide and luminol, a possible mechanism of this reaction was proposed. In the optimum conditions, CL intensities are proportional to concentrations of the phentolamine in the 0.01-1 microg/mL range. The limit of detection is 3.0 ng/mL for phentolamine. The method has been applied to the determination of phentolamine in the commercial preparations, synthetic samples and biological fluids with satisfactory results.

Development of hibernomas in rats dosed with phentolamine mesylate during the 24-month carcinogenicity study.

Phentolamine is a reversible competitive alpha-adrenergic antagonist with similar affinities for alphal and alpha2 receptors. It has a long history of safe clinical use, and was developed as a potential therapy for male erectile dysfunction because of its capacity to increase the arteriolar blood flow to the corpora cavernosa. Phentolamine mesylate was administered to rats by oral gavage at daily doses of 10, 50, and 150 mg/kg for 24 months. A dose-related increase in mortality, ascribed to an exaggerated pharmacologic effect, was seen at high doses. Systemic exposure as measured by plasma drug concentration increased with dose and duration of dosing and slight drug accumulation occurred, particularly in high-dose males. In the treated groups, 10 males and 1 female were diagnosed with hibernomas, neoplasms of brown adipose tissue, which appeared in the thoracic cavity or retroperitoneal area as circumscribed, tan to reddish-brown lobulated masses. Histologically, the masses were well circumscribed with variably sized lobules defined by a rich capillary network and consisted of closely apposed oval to polygonal cells with large amounts of cytoplasm and a centrally located nucleus. The cytoplasm's appearance varied from multivacuolated to univacuolated to granular eosinophilic. In a few cases, neoplastic emboli were observed in capsular vessels. Ultrastructurally, the neoplastic cells contained numerous mitochondria with transverse parallel cristae that occupied over 60% of the cytoplasm and lipid droplets. This study documents the previously unreported development of hibernomas in rats treated with phentolamine mesylate.

Phentolamine bioequivalence study.

OBJECTIVE: To assess the bioequivalence of 2 tablet formulations of phentolamine (Regitine phentolamine 40 mg tablet formulation by Novartis, Brazil, as test formulation, and Vasomax, phentolamine 40 mg tablet formulation by Schering Plough S.A., Brazil, as reference formulation). METHODS: A single 40 mg oral dose of each formulation was administered to 36 male healthy volunteers. The study was conducted after screening, using an open, randomized, 2-period crossover design, a 7-day interval between doses, and wash-out period of at least 4 weeks. Plasma samples for determination of phentolamine were obtained predose and at intervals over 720 min postdose. Plasma concentrations were quantified by reversed-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS) with positive ion electrospray ionization using multiple reactions monitoring (MRM) method. Precision of the method was evaluated using calibration curves and plasma quality control samples. The subjects were monitored throughout the study. Systolic and diastolic blood pressure and pulse rate measurement were taken predose and at intervals up to 720 min. Tolerance of both products was good. No serious adverse reactions were reported. The pharmacokinetic parameters calculated for both compounds included: AUC(0-720 min), AUC(0-infinity), C(max), Ca and k(e). RESULTS: The maximum concentrations reached (C(max)) were compared. Regitine 40 mg formulation C(max) geometric mean ratio was 108.29% (90% CI = 98.58-118.96) of Vasomax 40 mg formulation. The areas under the curve (AUC(0-720 min)) were compared. Regitine 40 formulation (AUC(0-720 min)) geometric mean ratio was 102.33% (90% CI = 97.21-107.72) of Vasomax 40 mg formulation. CONCLUSION: Since the 90% CI for both C(max) and AUC ratio where inside the 80 to 125% interval proposed by the Food and Drug Administration, it is concluded that Regitine 40 mg tablet is bioequivalent to Vasomax for the rate and extent of absorption.

Isoprenaline cannot act on pancreatic beta cells without hyperglycemia or alpha-block.

During long-term increase in isoprenaline (pronounced beta-effect) and isoprenaline plus regitine (pure beta-effect) pancreatic insulin-secretion still depended mostly on blood glucose levels. This means that increased beta-effect during normo- or hypoglycemia could not cause a higher insulin-secretion. Only during additional alpha-receptor blockade insulin-secretion was slightly but insufficiently increased. Catecholamines seem to be more regulator than originator of the insulin secretory process.

Spontaneous fall in blood pressure and reactivity of sympathetic nervous system in hospitalized patients with essential hypertension.

We evaluated whether reduction in sympathetic reactivity plays a major role in the spontaneous falls in blood pressure (BP) experienced during hospitalization by patients with essential hypertension. In the present case BP fell on the 2nd day of hospitalization. The responses of plasma catecholamines (CA) and BP to both handgrip and tilting were not altered during either the first 24 hours or the entire 7 days of hospitalization. The effect of phentolamine on BP was similar on the 1st, 2nd and 7th days. However, the resting levels of plasma norepinephrine before handgrip, tilting and phentolamine were significantly diminished on the 7th day, but not on the 2nd day. In conclusion, the diminution of sympathetic activity may be partly responsible for the hospitalization-induced fall in BP in the late stages.

Antagonism of bromobenzene-induced hepatotoxicity by phentolamine: evidence for a metabolism-independent intervention.

A previous study has revealed that phentolamine markedly antagonizes the bromobenzene-induced hepatotoxicity and lethality in B6C3F1 mice. One potential mechanism by which phentolamine may diminish the bromobenzene-induced hepatotoxicity is by a direct or indirect interference with the metabolism of bromobenzene to toxic metabolites. In the present study, phentolamine cotreatment failed to alter the elimination of bromobenzene from serum or the distribution of bromobenzene to liver. This suggests that phentolamine cotreatment does not indirectly interfere with bromobenzene bioactivation secondary to changes in bromobenzene absorption, distribution, or elimination. Further, a phentolamine concentration 10- to 20-fold greater than those measured in vivo failed to alter the in vitro metabolism of bromobenzene to its ortho- and para-phenolic metabolites. It is believed that para-bromophenol represents the rearrangement product of the hepatotoxic 3,4-epoxide and that ortho-bromophenol is a product of the nonhepatotoxic 2,3-epoxide pathway. Thus, it appears that phentolamine does not antagonize bromobenzene-induced hepatotoxicity by inhibiting the formation of hepatotoxic intermediates, nor by enhancing metabolism via the nonhepatotoxic pathway. On the basis of these studies, we conclude that phentolamine antagonism of bromobenzene-induced hepatotoxicity occurs through a mechanism independent of bromobenzene bioactivation.

[Changes in the density of human lymphocyte beta-adrenergic receptors in hypertension]. / Izmenenie plotnosti beta-adrenergicheskikh retseptorov limfotsitov cheloveka pri gipertonicheskoi bolezni.

The beta-adrenoreceptor density in intact lymphocytes of peripheral blood of normotensive and hypertensive adults was measured by the radioligand binding technique with the use of 3H-dihydroalprenolol. The density of beta-adrenoreceptors was found to be higher in lymphocytes of hypertensive subjects while the number of the receptors was equal to 2076 +/- 208 and 1461 +/- 175 receptors per cell, respectively, in hypertensive and normotensive subjects. The dissociation constants in both cases varied from 0.4 to 1.8 nM. Probably, the decreased responses to the adrenergic agents in hypertensive subjects are not connected with the decreased number of beta-adrenoreceptors and may be due to alterations in postreceptor events.

Interaction of clonidine and clonidine analogs with human platelet alpha 2-adrenergic receptors.

Several new clonidine analogs were synthesized and their ability to inhibit [3H]phentolamine binding to human platelet alpha 2-adrenergic receptors was tested. The order of potency and calculated dissociation constants for clonidine and its analogs were as follows: clonidine (0.020 +/- 0.005 microM) greater than p-aminoclonidine (0.100 +/- 0.010 microM) greater than hydroxy-phenacetyl-aminoclonidine (0.20 +/- 0.03 microM) greater than p-dansyl clonidine (1.00 +/- 0.20 microM) greater than t-boc-tyrosine clonidine (1.80 +/- 0.60 microM). Thus, p-amino substitution reduces alpha 2-adrenergic affinity in the platelet system. The effects of clonidine and its p-amino analogs on platelet adenylate cyclase were also evaluated. This enzyme is inhibited by epinephrine acting via alpha 2-adrenergic receptors. Both clonidine and p-aminoclonidine cause slight inhibition of basal adenylate cyclase and reverse the inhibition induced by epinephrine. These observations indicate that clonidine is a partial agonist for platelet alpha 2-adrenergic receptors.

Gas chromatographic determination of phentolamine (Regitine) in human plasma and urine.

A method for the determination of unconjugated phentolamine at concentrations down to 5 ng/ml in human plasma, and of free and total (free plus conjugated) phentolamine down to 25 ng/ml in urine is described. After addition of 2-[N-(p-chlorophenyl)-N-(m-hydroxyphenyl)-aminomethyl]-2-imidazoline as internal standard, both compounds are extracted into benzene-ethyl acetate (1:1, v/v) at pH 10, transferred into an acidic aqueous solution and back-extracted at pH 10 into benzene-ethyl acetate. They are then derivatized with N-heptafluorobutyrylimidazole. The derivatives are determined by gas chromatography using a 63Ni electron-capture detector. In urine, total (free plus conjugated) phentolamine is determined after enzymatic hydrolysis. The technique was applied for the study of the plasma concentrations and urinary elimination after oral administration to man.

Determination of the major metabolite of phentolamine in human plasma and urine by high-performance liquid chromatography.

A reversed-phase, high-performance liquid chromatographic method using UV detection is described for the assay of the major metabolite of phentolamine in plasma and urine before or after enzymatic hydrolysis. Plasma is deproteinized with methanol. The sensitivity limit is 200 ng/ml using 150-microliters samples. Urine is either diluted with water or purified after enzymatic hydrolysis. Concentrations down to 2--3 micrograms/ml could be quantified with acceptable precision. This method was applied to plasma and urine samples from subjects given phentolamine.

The adrenalin binding site on human platelets.

Using 3H-adrenalin the quantity and characteristics of the adrenalin receptors on human platelets were evaluated. Maximum adrenalin binding by intact platelets from eight normal subjects averaged 3.2 ng adrenalin/10(8) platelets, equivalent to 105 000 binding sites per platelet. Bound 3H-adrenalin could be dissociated or binding could be inhibited by an excess of unlabelled adrenalin, noradrenalin, isoproterenol or dopamine; phentolamine or propanalol had no effect on 3h-adrenalin binding, even in concentrations 10 000-fold greater. These studies show that the epinephrine binding site can be detected and quantitiated on human platelets and that its characteristics differ from those classically attributed to either alpha or beta adrenergic receptors.