Daniel J. Cushing

G proteins subserve relaxations mediated by adenosine receptors in human coronary artery.

The coupling of the human coronary adenosine receptor to a G protein was investigated in vitro. Hearts were obtained from accidental death victims and the left anterior descending coronary artery (LAD) was taken for experimentation. Cholera toxin (CT) and pertussis toxin (PT) ADP-ribosylated proteins with Mr of 45, 49 (CT), and 41 (PT) kDa. Both processes were sensitive to GTP7S. In LAD rings contracted with K.C1, adenosine (ADO) and its analogs 5‘-N-ethylcarbox-amidoadenosine (NECA) and 2-chloroadenosine (CAD) produced concentration-dependent relaxation. These concentration-response curves were shifted to the right significantly in the presence of the competitive ADO receptor antagonist, 8-phenyltheophylline (8-PT), indicating the involvement of ADO receptors. Treatment with NaF/AICI3 which uncouples G protein-mediated responses, caused significant attenuation of the relaxation responses to ADO. NECA, and CAD. When the rings were incubated with CT, there was an attenuation of the relaxations produced by ADO, CAD, NECA, and isoproterenol (ISOP). Incubation with PT resulted in significant inhibition of the relaxations induced by ADO, NECA, and CAD. The results provide evidence for the presence of CT- and PT-sensitive G protein(s) subserving the relaxing adenosine receptors in human coronary artery.

PM101: A cyclodextrin-based intravenous formulation of amiodarone devoid of adverse hemodynamic effects

Intravenous amiodarone (Amiodarone i.v.) is widely used to treat cardiac arrhythmias. The most frequent clinical adverse event associated with Amiodarone i.v. administration is systemic hypotension which has been attributed to the cosolvents used in the formulation, polysorbate 80 and benzyl alcohol. To minimize hypotension Amiodarone i.v. is diluted in 5% dextrose in water prior to administration and slowly infused. PM101 is a novel intravenous formulation that uses sulfobutylether-7-beta-cyclodextrin to solubilize amiodarone, and thus should be devoid of the untoward hemodynamic effects associated with polysorbate 80 and benzyl alcohol. Beagle dogs (n=7/group) were anesthetized with morphine and alpha-chloralose and instrumented to assess aortic blood pressure, cardiac output, cardiac contractility, and heart rate. Animals were treated with the U.S. approved human-equivalent loading dose (2.14 mg/kg) of Amiodarone i.v., PM101, and their respective vehicle controls. Administration of Amiodarone i.v. rapidly and significantly decreased mean aortic pressure, cardiac output, and cardiac contractility. A significant increase in heart rate was also observed as was a transient, but not significant, decrease in systemic vascular resistance. A similar pattern of rapid and significant hemodynamic changes was produced by the Amiodarone i.v. Vehicle (polysorbate 80/benzyl alcohol) alone. In marked contrast, PM101 and its vehicle produced no significant hemodynamic effects. This study provides a useful model for the continued search for a safe and effective intravenous amiodarone formulation devoid of the hypotensive risk associated with the current commercial formulation.

Reversal of heparin-induced increases in aPTT in the rat by PM102, a novel heparin antagonist

Protamine is the only agent approved to reverse heparin-induced anticoagulation. Due to the significant adverse effects of protamine there is an important need for an alternative agent with an improved safety profile. The pharmacodynamics of PM102, a novel peptide-based heparin antagonist, was evaluated and compared to protamine in a rat model. Rats were dosed with intravenous heparin (50U/kg) and 4min later with protamine (0.25, 0.75mg/kg single intravenous bolus) or PM102 (0.1, 0.3, 1, 3, 30mg/kg single intravenous bolus). Blood samples were collected though 60min for assessment of activated partial thromboplastin time (aPTT) and plasma concentration of PM102. Both doses of protamine markedly lowered the elevated aPTT to baseline values within 1 to 5min after administration. PM102 (0.3-30mg/kg) also rapidly and completely reversed heparin-induced increases in aPTT within 1 to 5min. The effects of PM102 administered as an infusion over 10min also reversed aPTT with similar potency to that observed for bolus administration. The onset of reversal with infusion was delayed relative to the same total dose given as a bolus; however, the maximum effect was similar. PM102 rapidly (T(max) 1-2.6min) appeared in plasma after dosing. Concentrations of PM102 generally declined rapidly after reaching T(max) with a mean T(1/2) of 4 to 31min. PM102 is a novel synthetic peptide that effectively reverses the anticoagulant effect of heparin. Its utility as a bolus injection as well as infusion, its rapid efficacy and its rapid clearance make this an ideal candidate for clinical development.

PM101: intravenous amiodarone formulation changes can improve medication safety

Importance of the field: Intravenous amiodarone (A-IV) is used to manage ventricular and atrial arrhythmias. The current formulation uses polysorbate 80 and benzyl alcohol to maintain amiodarone in solution, and these co-solvents are linked with clinically-important adverse events and pharmaceutical incompatibilities. PM101 is a recently FDA-approved intravenous formulation of amiodarone that uses a cyclodextrin to solubilize amiodarone. Areas covered in this review: This review describes the clinical and pharmaceutical development of formulations of amiodarone for intravenous administration. The medical and pharmaceutical literature was searched for papers discussing A-IV, PM101 and their formulation components. Relevant literature was identified starting from 1948 to the present. What the reader will gain: The reader will learn about the important medical and pharmaceutical issues complicating A-IV administration, including an understanding of related hypotension and compatibility with commonly used infusion materials and how these issues may impact drug safety. PM101 has been developed to address several of these important issues. Take home message: PM101 is a new formulation of A-IV that is stable in commonly used infusion materials and avoids co-solvent related toxicities.

Characterization of adenosine binding sites in bovine testicular tissue using 8-cyclopentyl-1,3-[3H]dipropylxanthine☆

The existence of specific adenosine binding sites in bovine testicular tissue was evaluated using the novel antagonist radioligand 8-cyclopentyl-1,3-[3H]dipropylxanthine ([3H]DPCPX). Saturation analysis revealed specific binding that was saturable at approximately 1 nM. Scatchard analysis indicated a single class of binding sites with a KD = 0.26 nM and a Bmax = 0.37 pmol/mg protein. Affinity profiles suggest an A1 subtype recognition site that is different from the classical A1 adenosine receptor. The results presented should prove useful in subsequent studies concerning heterogeneity among adenosine receptors and also aid in discerning the role of adenosine in reproduction.

Pharmacokinetics and platelet aggregation inhibitory effects of a novel intravenous formulation of clopidogrel in humans.

1. PM103 is an intravenous formulation of clopidogrel being developed as an alternative to oral clopidogrel to provide for dosing flexibility in the emergent clinical setting. The present first‐in‐human study assessed the pharmacokinetic and pharmacodynamic effects of PM103 and its safety in 144 healthy human subjects.

The hypotensive effect of intravenous amiodarone is sustained throughout the maintenance infusion period

1. Hypotension frequently occurs with use of intravenous amiodarone and is managed by slowing the rate of administration. This response has been attributed to the cosolvents in the formulation and is believed to be solely related to the initial loading dose. The present study was performed to determine whether intravenous amiodarone‐induced hypotension persists beyond the loading dose and into the maintenance infusion period and also whether hypotension occurs with maintenance level dosing alone.

Bioequivalence of 2 Intravenous Amiodarone Formulations in Healthy Participants

Intravenous amiodarone is an effective agent for the treatment of recurrent ventricular fibrillation and hemodynamically unstable ventricular tachycardia. PM101 is a new formulation of intravenous amiodarone that uses a cyclodextrin to maintain amiodarone in the aqueous phase. Eighty‐eight participants were enrolled in this randomized, double‐blind, crossover, bioequivalence clinical study and were treated with single doses (150 mg) of PM101 and intravenous amiodarone separated by a washout period of at least 42 days. Venous blood samples were taken periodically during the first 72 hours after dosing to determine standard pharmacokinetic parameters. The amiodarone plasma concentration‐time curve observed with both formulations was virtually identical, as was the 72‐hour area under the curve (AUC0–72). Similar equivalence was seen for desethylamiodarone, the active metabolite of amiodarone. The geometric ratios of the AUC0–72 for amiodarone and desethylamiodarone were 1.03 (95% confidence interval [CI], 1.00–1.06) and 1.01 (0.99–1.03), respectively. Similar geometric ratios and CIs were found for maximum plasma concentration (Cmax) and for AUC extrapolated to infinity (AUC0‐∞). Because the ratios and their CI fell between the limits of 0.8 and 1.25, bioequivalence of these 2 formulations was established. No safety concerns unique to PM101 were identified.

Interaction of the β adrenergic receptor antagonist bucindolol with serotonergic receptors

Bucindolol is a nonselective beta-adrenergic receptor antagonist that has additional vasodilating properties. Because some beta-adrenergic receptor antagonists such as cyanopindolol are used as 5-HT1A/5-HT1B receptor antagonists, we tested the hypothesis that bucindolol can interact with 5-HT receptors. Both in vitro and in vivo methods were used to examine the interaction of bucindolol with 5-HT receptors relevant to the cardiovascular system-the 5-HT1A, 5-HT1D, 5-HT2A, and 5-HT2B receptors-and with alpha1-adrenergic receptors. In binding studies, bucindolol displayed high affinity for the 5-HT1A receptor (Ki, 11 nM), modest affinity for the 5-HT2A receptor (Ki, 382 nM), and no measurable affinity for the 5-HT1D receptor; binding affinity for the 5-HT2B receptor was not studied. Bucindolol also displayed significant binding affinity (Ki, 69 nM) for the alpha1-adrenergic receptors. Alpha1-Adrenergic receptor antagonist activity was confirmed by the ability of bucindolol (1 mg/kg) to act as a competitive antagonist against 0.01-30 microg/kg phenylephrine-induced pressor responses in conscious rats. In conscious permanently instrumented rats, bucindolol (0.1-3.0 mg/kg, i.v.) did not cause bradycardia similar to that elicited by the 5-HT1A-receptor agonist 8-OH-DPAT (3-300 microg/kg, i.v.), nor did bucindolol (1 mg/kg) block the 8-OH-DPAT-induced bradycardia. Bucindolol (10(-9)-10(-5) M) did not cause relaxation in the PGF2alpha-contracted, endothelium-intact porcine coronary artery, nor did bucindolol (10(-5) M) block 5-HT-induced coronary artery relaxation, indicating that bucindolol does not have significant interactions at the 5-HT1D receptor. Bucindolol also displayed no agonist activity at the 5-HT2A and 5-HT2B receptor (endothelium-denuded rat thoracic aorta and rat stomach fundus, respectively), but did act as a weak 5-HT2A-receptor antagonist (-log K(B) [M] = 5.4+/-0.1) and 5-HT2B-receptor antagonist (-log K(B) [M] = 7.8+/-0.1). Thus, these data suggest that bucindolol lacks the ability to activate the 5-HT1A, 5-HT1D, 5-HT2A, and 5-HT2B receptor, but can block alpha1-adrenergic receptors and act as a weak 5-HT2A- and 5-HT2B-receptor antagonist. The relevance of these serotoninergic effects as it pertains to the mechanism of bucindolol-induced vasodilation is unknown.

Comparative Bioavailability of a Premixed, Ready-to-Use Formulation of Intravenous Amiodarone With Traditional Admixture in Healthy Subjects

Intravenous amiodarone is an effective agent for the treatment of recurrent ventricular fibrillation and hemodynamically unstable ventricular tachycardia. PM101 Premixed Injection is a new formulation of intravenous amiodarone that uses a cyclodextrin to maintain amiodarone in the aqueous phase. Eighty‐eight subjects were enrolled in this randomized, single‐blind, crossover, bioequivalence clinical study and were treated with single doses (150 mg) of PM101 Premixed Injection and intravenous amiodarone separated by a washout period of at least 42 days. Venous blood samples were taken periodically during the first 72 hours after dosing to determine standard pharmacokinetic parameters. The geometric ratio of the area under the concentration‐time curve for time 0–72 hours (AUC0–72hr) for amiodarone was 0.96 (95% confidence interval [CI], 0.94–0.99). The geometric ratio of the maximum concentration (Cmax) for amiodarone was 0.87 (95% CI, 0.84–0.91). Because these ratios and their CI fell between the limits of 0.8 and 1.25, bioequivalence of these 2 formulations was established. No safety concerns unique to the PM101 Premixed Injection, ready‐to‐use formulation were identified.