Microarrays and microneedle arrays for delivery of peptides, proteins, vaccines and other applications.

INTRODUCTION: Peptide and protein microarray and microneedle array technology provides direct information on protein function and potential drug targets in drug discovery and delivery. Because of this unique ability, these arrays are well suited for protein profiling, drug target identification/validation and studies of protein interaction, biochemical activity, immune responses, clinical prognosis and diagnosis and for gene, protein and drug delivery. AREAS COVERED: The aim of this review is to describe and summarize past and recent developments of microarrays in their construction, characterization and production and applications of microneedles in drug delivery. The scope and limitations of various technologies in this respect are discussed. EXPERT OPINION: This article offers a review of microarray/microneedle technologies and possible future directions in targeting and in the delivery of pharmacologically active compounds for unmet needs in biopharmaceutical research. A better understanding of the production and use of microarrays and microneedles for delivery of peptides, proteins and vaccines is needed.

Gender differences in cardiac repolarization following intravenous sotalol administration.

BACKGROUND: Females are more susceptible to drug-induced torsade de pointes (TdP), which is associated with excessive prolongation of the heart rate-corrected QT interval (QTc). Sotalol prolongs the cardiac action potential that can be observed as QT prolongation and can induce TdP. The aim of this study was to assess gender differences in sotalol-induced QTc prolongation. METHODS: A total of 15 healthy volunteers, 9 female and 6 male (age: 32 ± 8 years) received 75 mg intravenous sotalol over 2.5 hours at a constant infusion rate. A 12-lead electrocardiograph (ECG) was recorded at baseline, 0.5, 1, 2, 3, 4, and 5 hours following the start of the infusion, and blood samples were collected simultaneously. QTc was calculated by the Fridericia and Framingham formulas. The 2 formulas resulted in virtually identical QTc intervals. The data analysis included repeated measures of analysis of variance (ANOVA), univariate analysis, and linear regression analysis. RESULTS: The longest average QTc intervals were observed at 2 hours of sotalol infusion in both genders. Compared to baseline, the increase was very significant in females (411 ± 13 vs 438 ± 13 ms, P < .001), while it was less significant in males (395 ± 23 vs 413 ± 27 ms, P < .05). The magnitude of individual changes from baseline were greater in females than in males (34 ± 8 vs 21 ± 12 ms, P < .05). In each gender, QTc and serum sotalol concentration strongly correlated (r = .93, P < .001). An upward shift of the regression line in females indicates a longer QTc at any concentration level. Males had greater body weight and body surface area than females (P < .05) but neither correlated with QTc or predicted QTc prolongation. The univariate analysis indicated that the single predictor for the greater QTc prolongation was female gender. CONCLUSION: Females had greater QTc prolongation than males following sotalol administration. This enhanced response to drug action may explain the higher incidence of drug-induced TdP seen in females.

Recent advances in prodrugs as drug delivery systems.

Prodrugs are a class of drug derivatives with little or no pharmacological activity that are converted in vivo to therapeutically active compounds. The primary utility of a prodrug approach is to improve pharmaceutical properties. Because it does not alter the primary structure of the parent drug, the synthesis of prodrugs is usually much less difficult than the synthesis of analogs. The derived physicochemical properties of the resulting derivatives can be carefully tailored by means of structural modification of the promoiety. However, sufficient levels of intrinsic activity of the parent drug need to be assured through in vivo cleavage of the prodrug. The prodrug approach has been successfully applied to a wide variety of drugs. This article briefly discusses advances in strategies for development of prodrugs and their mechanisms of drug release.

QT prolongation and serum sotalol concentration are highly correlated following intravenous and oral sotalol.

OBJECTIVES: The aim of this study was to evaluate the correlation between QT interval (QT) and serum sotalol concentration following a single low dose of oral and intravenous sotalol. METHODS: Fifteen healthy volunteers received 75 mg intravenous sotalol over 2.5 h and 80 mg oral sotalol in a random order. Serum sotalol concentrations and 12-lead electrocardiograms were obtained simultaneously at baseline and 7 times following dosings. Rate-corrected QT (QTc) was calculated by the Bazett, Fridericia and Framingham formulas. Linear regression analysis was performed between sotalol concentrations and QT measurements. RESULTS: Significant QT prolongation was seen at very low sotalol doses and serum concentrations. QTc intervals calculated by the Framingham and Fridericia formulas showed the strongest and virtually identical correlations with serum sotalol concentration (r >or= 0.97, p < 0.001) following oral and intravenous administrations. The equation QTc = 0.0342 (sotalol concentration) + 398 closely predicted actual QTc at any sotalol concentration. CONCLUSIONS: A strong correlation was observed between serum sotalol concentration and QTc prolongation across the entire concentration range. Low-dose sotalol caused significant QT prolongation. At similar concentrations, intravenous and oral sotalol caused similar QT and QTc effects. Knowing the QT effect can be used to guide further dose increase.

Developing a safe intravenous sotalol dosing regimen.

Recently, an intravenous formulation of sotalol has been approved by the food and drug administration for substitution for oral therapy in patients who are unable to take oral sotalol. The purpose of this randomized, 2-treatment, 2-period, crossover study was to develop a safe dosing regimen for intravenous sotalol that provides similar blood levels and therefore similar efficacy and safety to orally administered sotalol. Fifteen healthy subjects received 75 mg intravenous sotalol infusion administered over 2.5 hours and 80 mg oral sotalol. Standard pharmacokinetic methods were used to obtain maximum serum concentrations (Cmax) and areas under the concentration-time curves (AUC). Individual pharmacokinetic parameters were used in simulation studies to determine the optimal intravenous administration regimen. Intravenous sotalol administered over 2.5 hours resulted in a significantly greater Cmax than oral administration (830 +/- 391 vs. 601 +/- 289 ng/mL, P < 0.001). With increasing the length of infusions to 3, 4, and 5 hours, simulation studies showed that the Cmax decreased to 128%, 113%, and 102% of the oral Cmax. The length of infusion did not affect AUC. Based on these studies, a safe intravenous regimen for the replacement of 80-mg oral therapy requires 75 mg intravenous sotalol administered as a 5-hour infusion. Because the pharmacokinetics of sotalol are linear and dose proportional, 150 mg intravenous sotalol administered over 5 hours will provide similar Cmax and AUC as 160 mg oral sotalol. The food and drug administration-approved dosing regimen is 75 mg intravenous sotalol to replace 80 mg oral sotalol and 150 mg intravenous sotalol to replace 160 mg oral sotalol, both administered over 5 hours.

The additive effects of the active component of grapefruit juice (naringenin) and antiarrhythmic drugs on HERG inhibition.

BACKGROUND: Grapefruit juice causes significant QT prolongation in healthy volunteers and naringenin has been identified as the most potent human ether-a-go-go-related gene (HERG) channel blocker among several dietary flavonoids. The interaction between naringenin and I(Kr)-blocking antiarrhythmic drugs has not been studied. We evaluated the effect of combining naringenin with I(Kr)-inhibiting antiarrhythmic drugs on cardiac I(Kr). METHODS AND RESULTS: I(Kr) current was studied by using HERG expressed in Xenopus oocytes, and the two-electrode voltage clamp technique was employed. Antiarrhythmic drugs (azimilide, amiodarone, dofetilide and quinidine) were tested. Experiments were performed at room temperature. Naringenin blocked HERG current dose dependently with an IC(50) of 173.3 +/- 3.1 microM. Naringenin 100 microM alone inhibited HERG current by 31 +/- 6%, and this inhibitory effect was increased with coadministration of 1 or 10 microM antiarrhythmic drugs. When 100 microM naringenin was added to antiarrhythmic drugs, greater HERG inhibition was demonstrated, compared to the current inhibition caused by antiarrhythmic drugs alone. Addition of naringenin significantly increased current inhibition (p < 0.05). CONCLUSIONS: There is an additive inhibitory effect on HERG current when naringenin is combined with I(Kr)-blocking antiarrhythmic drugs. This additive HERG inhibition could pose an increased risk of arrhythmias by increasing repolarization delay and possible repolarization heterogeneity.

Extracellular acidification and hyperkalemia induce changes in HERG inhibition by ibutilide.

BACKGROUND: A high incidence of proarrhythmia has been reported with ibutilide, especially in patients with underlying heart diseases. Our previous studies have shown that extracellular acidosis and hyperkalemia attenuate the HERG-inhibitory effect of proarrhythmic drugs, e.g. quinidine, but have little impact on the less-proarrhythmic drug amiodarone. We hypothesized that ibutilide would behave like quinidine in the presence of extracellular acidosis and hyperkalemia. METHODS AND RESULTS: HERG was expressed on Xenopus oocytes, and the two-electrode voltage clamp technique was employed. Our results showed that ibutilide was a potent HERG inhibitor. When extracellular solution contained 5 mM KCl and pH was 7.4, the IC(50) of ibutilide was 0.9 +/- 0.1 microM. The inhibitory effect of ibutilide was attenuated when extracellular pH decreased to 6.2. There was a significant difference in current inhibition by ibutilide at pH 7.4 versus pH 6.2 (p < 0.01). When the extracellular potassium concentration was increased from 5 to 10 mM, ibutilide produced less current inhibition, and the IC(50) was increased to 2.0 +/- 0.1 microM. CONCLUSION: Extracellular acidosis and hyperkalemia attenuate the HERG-inhibitory effect of ibutilide. The differences in HERG inhibition between acidic and hyperkalemic regions compared to normal regions in the myocardium may result in heterogeneity in repolarization, which may contribute to the proarrhythmic toxicity of ibutilide.

The effects of quinidine and its chiral isolates on erg-1sm potassium current and correlation with gastrointestinal augmentation.

Smooth-muscle erg 1 (erg1-sm) potassium channel has been recently reported to participate in the modulation of gastrointestinal contractility. Because quinidine inhibits cardiac potassium channel and as a result augments gastrointestinal contractility, it was thought that quinidine may affect erg1-sm. Studies were undertaken to evaluate the effects of quinidine and its chiral isolates on gastrointestinal erg1-sm potassium current and correlate these effects with colon contractility. Chiral separation (high-performance liquid chromatography technique), mass spectrometry, and optical rotation determination were performed to obtain chiral isolates needed for experiments. The erg1-sm potassium channel was expressed in Xenopus oocytes, and the two-electrode patch clamp technique was employed for recording. An isolated rat colon preparation was employed to measure changes in contractility. As a result of chiral separation, two peaks were obtained with elution times of 8.31 and 8.66 minutes, both with a molecular weight of 324; the optical rotations of racemate isolates X and Y were: +258 degrees, +/-0 degrees; and +217 degrees, respectively. The percentage changes in amplitudes of colon contraction (from baseline) were determined at different concentrations of quinidine and for the two isolates in five experiments in each group. Quinidine 0.1, 1, and 10 microM increased contractility by 79 +/- 34, 125 +/- 42, and 217 +/- 51 (P < or = 0.05); for isolate X, the values were 70 +/- 20, 115 +/- 32, and 272 +/- 32 (P < or = 0.05), and for isolate Y the values were 22 +/- 12, 46 +/- 17, and 59 +/- 22. The inhibition of erg1-sm currents by quinidine was 19 +/- 4, 21 +/- 5, and 48 +/- 6 (P < or = 0.05), respectively; that by isolate X was 20 +/- 4, 23 +/- 5, and 39 +/- 7 (P < or = 0.05), and that by isolate Y was 22 +/- 4, 21 +/- 4, and 31 +/- 6. One chiral isolate and quinidine markedly augmented contractility, whereas quinidine and the two chiral isolates inhibited the erg1-sm potassium currents to a similar extent. These results suggest that erg1-sm inhibition does not explain gastrointestinal contractile augmentation caused by the quinidine racemate and its chiral isolates.

The evaluation of the diuretic action of parenteral formulations of metolazone.

BACKGROUND AND OBJECTIVES: This study was design to compare the diuretic and natriuretic effects of the 2 parenteral formulations of metolazone and the combination of these 2 formulations of metolazone with the parenteral administration of furosemide. Metolazone is an anthracrene acid derivate and manifests a dual diuretic effect on the proximal and distal tubule with a minimal kaluretic effect. It is currently only marketed in an orally administrable formulation, and this has limited its utility in critically ill patients. Metolazone given orally and furosemide given orally or parenterally are frequently administrated together when furosemide alone is clinically inadequate at producing a desired diuresis. METHODS: Sprague Dawley male rats (400 to 450 g) were divided into groups to receive a parenteral formulation of metolazone or furosemide administrated separately intraperitoneally (IP) or administrated IP in combination with one another. Tris buffer-administered IP was used as a control vehicle comparator. The urine volume voided over the following 24 hours was collected, measured and analyzed for sodium content. RESULTS: Vehicle (Tris buffer) caused 9 +/- 1 mL/d output of urine with a sodium [Na+] concentration of 194 +/- 41 micromol/L (n=6 per group). Metolazone 2 mg/kg resulted in 16 +/- 3 mL/d urine output and sodium [Na+] of 278 +/- 76 micromol/L (n=6 per group). Furosemide 2, 4, and 6 mg/kg resulted in a volume of urine 9 +/- 1, 14 +/- 2 and 17 +/- 2 mL/d and [Na+] micromol/L of 194 +/- 41, 206 +/- 108, and 229 +/- 91, respectively. Metolazone 4 mg/kg combined with furosemide 4 mg/kg resulted in a urine volume of 21 +/- 1 mL/d and [Na+] of 326 +/- 108 micromol/L. CONCLUSION: Combining metolazone and furosemide can cause an increase in urine volume and sodium excretion. Metolazone administrated parenterally in combination with the parenteral administration of furosemide appears to have an important clinical potential.

The effect of high extracellular potassium on IKr inhibition by anti-arrhythmic agents.

BACKGROUND: Hyperkalemia is a potentially life-threatening disorder frequently occurring in hospitalized patients. The ischemic myocardium releases potassium into the extracellular space which can cause regional hyperkalemia. These changes may modify the effects of anti-arrhythmic drugs acting on the rapid component of the delayed rectifier potassium current (IKr). We evaluated the influence of increased extracellular potassium concentration [K(+)](e) on IKr inhibition by amiodarone, azimilide, dofetilide, quinidine and sotalol. METHODS AND RESULTS: Experiments were performed at room temperature. IKr current was studied by using HERG gene expressed in Xenopus oocytes as a model of cardiac IKr. Two-electrode voltage clamp technique was employed. The recording bath solutions contained either 5 or 10 mmol/l KCl. Amiodarone, azimilide, dofetilide, quinidine and sotalol all produced a dose-dependent inhibition of HERG current. At 5 mmol/l [K(+)](e), the IC(50) was 37.0 +/- 12.5 microM for amiodarone, 5.8 +/- 0.4 microM for azimilide, 1.5 +/- 0. 2 microM for dofetilide, 9.1 +/- 1.5 microM for quinidine, and 5.1 +/- 0.8 mM for sotalol. Raising the extracellular potassium to 10 mmol/l, HERG block by azimilide, dofetilide, quinidine and sotalol was significantly decreased, while the block by amiodarone was unchanged. The differences in the percentage current block produced by 3 microM drugs at 5 and 10 mmol/l [K(+)](e) were: -0.9% for amiodarone, 13.8% for quinidine, 20.5% for azimilide, and 16.2% for dofetilide. The differences in percentage block between 5 and 10 mmol/l [K(+)](e) by sotalol 10 and 30 mM were 7.1 and 5.6%. At 10 mmol/l [K(+)](e), the IC(50) was increased for azimilide, dofetilide, quinidine and sotalol but not for amiodarone; the IC(50) was 24.7 +/- 7.4 microM for amiodarone, 29.3 +/- 3.9 microM for azimilide, 2.7 +/- 0.2 microM for dofetilide, 27.6 +/- 4.0 microM for quinidine, and 7.2 +/- 1.7 mM for sotalol. CONCLUSION: Inhibition of IKr by azimilide, quinidine, dofetilide and sotalol was diminished by increasing [K(+)](e), while the inhibition by amiodarone was unchanged at normal and high [K(+)](e). The differential effects of azimilide, dofetilide, quinidine and sotalol at normal and high [K(+)](e) could be pro-arrhythmic by favoring re-entry arrhythmias. These results further support the unique electrophysiological effect of amiodarone.

Phenothiazine molecule provides the basic chemical structure for various classes of pharmacotherapeutic agents.

The chemical structure of phenothiazine provides a most valuable molecular template for the development of agents able to interact with a wide variety of biological processes. Synthetic phenothiazines (with aliphatic, methylpiperazine, piperazine-ethanol, piperazine-ethyl, or piperidine side-chain) and/or phenothiazine-derived agents e.g., thioxanthenes, benzepines, imonostilbenes, tricyclic antidepressants, dimetothiazine, and cyproheptadine have been effective in the treatment of a number of medical conditions with widely different etiology. These include various currently clinically used drugs for their significant antihistamic, antipsychotic, anticholinergic (antiparkinson), antipruritic, and/or antiemetic properties. They are also employed, although to a minor extent, as antidepressants, antispasmodics, analgesics, and antiarrhythemics. Some of these agents are also useful as anti-inflammatory, coronary vasodilator, radioprotective, sedative, antitussive, and skeletal muscle-relaxing medication. Still, others show different degrees of effectiveness as antibacterials, anthelmintics, antimalarials, or local anesthetics; a few are valuable in the control of acute migraine attacks and intractable hiccough. Adding to the seemingly ever-expanding therapeutic use of phenothiazine derivatives, a number of "old" and newly synthesized compounds e.g., "half-mustard-type" and benzo[alpha]phenothiazines, appear to be helpful as multidrug resistance modifiers, a property of particular importance in cancer chemotherapy. Some phenothiazines inhibit human plasmatic leucine-enkephalin aminopeptidase(s), enzymes known to regulate the turnover rate of a wide range of bioactive substances. These findings could lead to the design of new therapeutic treatment modalities for conditions such as Alzeimer's and Creutzfeldt-Jakob disease. Hopefully, this work will help to the rational design of new and improved pharmacological approaches based on a better understanding of the correlation between chemical structure, pharmacodynamic properties, and pharmacological activity of various phenothiazines and phenothiazine-derived classes of drugs.

The differential antibacterial and gastrointestinal effects of erythromycin and its chiral isolates.

The use of erythromycin has been limited by the gastrointestinal side effect properties, which include abdominal distress and diarrhea. To evaluate the possibility of reducing the toxicity of erythromycin, studies were undertaken to separate erythromycin into chiral isolates and then to test the activity of these chiral isolates on gastrointestinal contractility and bacteriostatic actions. Gastrointestinal contractility was obtained by the use of isolated strips of a rat colon. Antibacterial activity was used by obtaining the MICs of erythromycin and isolated agents against Enterococcus faecalis ATCC 29212. ANOVA was performed using the SPSS v.10 to determine statistical differences in the MICs and the amplitude and frequency of spike bursts. Results were expressed as mean+/-SE (N=5). The MICs (microg/mL) of erythromycin (racemate), chiral isolate X, and chiral isolate Y were 0.45+/-0.29, 0.53+/-0.24 (n.s.), and 0.2+/-0.07 (P

Chiral cardiovascular drugs: an overview.

Stereochemistry in drug molecules is rapidly becoming an important aspect in drug research, design, and development. Recently, individual stereoisomers of drug molecules with asymmetric centers such as fexofenadine, cetirizine, verapamil, fluoxetine, levalbutarol, and amphetamine, for example, have been separated and developed as individual drugs. These stereoisomers have different therapeutic activity, and each isomer has contributed differently with respect to its formulation's pharmacologic activity, side effects, and toxicity. The present overview discusses chirality among a select group of cardiovascular drugs, their stereochemical synthesis/preparation, isolation techniques using chiral chromatography, methods for confirmation of their enantiomeric purity, pharmacodynamics, and pharmacokinetics. Chirality has been visualized as an important factor in cardiovascular research. It is also becoming evident in other areas of therapeutics.

A mechanism for the potential proarrhythmic effect of acidosis, bradycardia, and hypokalemia on the blockade of human ether-a-go-go-related gene (HERG) channels.

Many drugs are proarrhythmic by inhibiting the cardiac rapid delayed rectifier potassium channel (IKr). In this study, we use quinidine as an example of highly proarrhythmic agent to investigate the risk factors that may facilitate the proarrhythmic effects of drugs. We studied the influence of pacing, extracellular potassium, and pH on quinidine's IKr blocking effect, all potential factors influencing quinidine's cardiac toxicity. Since the HERG gene encodes IKr, we studied quinidine's effect on HERG expressed in Xenopus oocytes by the 2-electrode voltage clamp technique. When extracellular K+ was 5 mmol/L, quinidine blocked the HERG current dose dependently, with an IC50 of 6.3 +/- 0.2 micromol/L. The blockade was much more prominent at more positive membrane potentials. The inhibition of HERG by quinidine was not use dependent. There was no significant difference between block with or without pacing. When extracellular K+ was lowered to 2.5 mmol/L, the current inhibition by quinidine was enhanced, and IC50 decreased to 4.6 +/- 0.5 micromol/L. At 10 mmol/L extracellular K+, there was less inhibition by quinidine and the IC50 was 11.2 +/- 3.1 micromol/L. Extracellular acidification decreased both steady state and tail currents of HERG. We conclude that the inhibitory effect of quinidine on IKr was decreased with extracellular acidification, which may produce heterogeneity in the repolarization between normal and ischemic cardiac tissue. Thus, the use-independent blockade of IKr by QT-prolonging agents such as quinidine may contribute to cardiac toxicity with bradycardia, hypokalemia, and acidosis further exaggerating the proarrhythmic potential of these agents.

The effect of magnesium sulfate on action potential duration and cardiac arrhythmias.

To evaluate the electrophysiologic and antiarrhythmic effects, Mg was infused at 15 mg/h (n = 5) or an equal volume of saline (1.2 mL/h) (n = 5) and electrocardiogram and action potential duration (APD) recorded every 15 minutes. Rats were anesthetized with 70 mg/kg pentobarbital intraperitoneally. Mg increased QT 15 +/- 6% on average compared with 1 +/- 4 for saline P < 0.01. Mg increased QT, 0, 0, 6 +/- 4, 13 +/- 5, 16 +/- 4, 23 +/- 5, 29 +/- 8, and 32 +/- 5% over baseline after a 2 hours infusion (P < 0.01). APD increased by 0, 6 +/- 3, 8 +/- 8, 14 +/- 4, 16 +/- 12, 21 +/- 4, 25 +/- 5% change from baseline (P < 0.05). The mean percentage of increase was 12 +/- 8 for the Mg group and 1 +/- 3 for the saline group (P < 0.05). The JT interval also increased after Mg (P < 0.01). After Mg loading, coronary occlusion of the left anterior descending coronary artery was performed. Ventricular premature contractions (VPCs), ventricular tachycardia (VT), and ventricular fibrillation (VF) were frequent in the saline control group, with 2 dying in VF; with only scattered VPCs and short runs of nonsustained VT in the Mg group. The results of these findings indicate that infusion of MgSO4 can prolong the QRS, QT, and JT intervals in the rat and these changes correlate well with arrhythmia suppression.

The influence of extracellular acidosis on the effect of IKr blockers.

BACKGROUND: Myocardial infarction causes the acidification of the cellular environment and the resultant acidosis maybe arrhythmogenic. The effect of acidosis on the action of antiarrhythmic drugs, an important issue in the antiarrhythmic drug therapy after myocardial infarction, remains to be studied. METHODS: To evaluate the effect of acidosis on rectifier potassium current (Ikr) blockers, the human ether-a-go-go-related gene (HERG), which encodes IKr, was expressed in Xenopus laevis oocytes. The two electrodes voltage clamp technique was used and the experiments were performed at room temperature. RESULTS: Quinidine (10 microM) inhibited HERG tail current by 37% +/- 5% at pH7.4. The block decreased to 5% +/- 2% with extracellular pH at 6.2. Dofetilide (0.3 microM) inhibited HERG tail current by 34% +/- 3% and 1% +/- 2% at extracellular pH 7.4 and 6.2, respectively. Azimilide (10 microM) inhibited HERG tail current by 59% +/- 3% and 17% +/- 3% at extracellular pH 7.4 and 6.2. There were significant differences in the HERG inhibition by quinidine, dofetilide, and azimilide between pH 7.4 and pH 6.2 (P < .01). The drug concentration blocking 50% of current (IC50) was 5.8 +/- 0.3 microM for azimilide, 9.9 +/- 1.0 microM for quinidine, and 0.5 +/- 0.02 microM for dofetilide at pH 7.4. When extracellular pH was decreased from 7.4 to 6.2, the IC50 increased to 95.5 +/- 11.3 microM for azimilide, 203.2 +/- 15.7 microM for quinidine, and 12.6 +/- 1.2 microM for dofetilide. Unlike quinidine, dofetilide, and azimilide, there was no significant difference in the percentage of current block by amiodarone between pH 6.2 and 7.4. For amiodarone, the IC50 was 38.3 +/- 8.5 microM at pH 7.4 and 27.3 +/- 1.6 microM at pH 6.2. CONCLUSION: Our data show that the Ikr blocking effect of azimilide, dofetilide, and quinidine was attenuated at acid pH, whereas this was not the case for amiodarone. These observations may explain the efficacy of amiodarone in reducing arrhythmic death in patients after a myocardial infarction compared with other IKr blockers.

Pharmacology and toxicology of a new aqueous formulation of intravenous amiodarone (Amio-Aqueous) compared with Cordarone IV.

Hypotension is the most frequent adverse event reported with intravenous amiodarone (Cordarone IV). The hypotension has been attributed to the vasoactive solvents of the formulation, polysorbate 80 and benzyl alcohol, both known to exhibit negative inotropy and hypotensive effect. A new aqueous formulation of intravenous amiodarone (Amio-Aqueous) does not contain vasoactive excipients and may be less toxic and cause less hypotension than Cordarone IV. This hypothesis was tested in a series of animal studies with direct comparison of Amio-Aqueous and Cordarone IV. All studies were performed on Sprague-Dawley rats. The acute toxicology study showed that both LD50 and LD100 were 30% greater for Amio-Aqueous than for Cordarone. At the dose at which all animals expired on Cordarone, 50% of animals were still alive on Amio-Aqueous. The study on myocardial contractility showed that Amio-Aqueous was a far less negative inotropic than Cordarone IV (P < 0.001). Amio Aqueous did not have an effect on contractility at 5- and 10-mg/kg dose levels while Cordarone resulted in a 25% (P < 0.01) and 29% (P < 0.002) decrease, respectively. The study on arterial blood pressure showed that Cordarone caused a significant decrease in blood pressure at each of the 3, 5, 10, and 20 mg/kg doses (P < 0.05 to P < 0.001) while Amio-Aqueous did not. The study on the antiarrhythmic effects showed comparable efficacy for both formulations. In conclusion, Cordarone IV was more toxic and caused significant hypotension and negative inotropy while Amio-Aqueous lacked the hypotensive and cardiotoxic properties of Cordarone. Therefore, Amio-Aqueous is a safer alternative than the standard formulation.

Inhibition of human plasma leucine5-enkephalin aminopeptidase hydrolysis by various endogenous peptides and a select number of clinically used drugs.

We identified a number of clinically used drugs and biologically active endogenous peptides able to significantly decrease the rate of human plasmatic aminopeptidase (AP) leucine-enkephalin (LEU) degradation. Bacitracin, bestatin, fluvoxamine, and each of 4 peptides tested significantly increased, in a dose-dependent manner (10-10 M), LEU degradation half-life (t1/2) in each of 5 plasma samples studied. Each sample was obtained by pooling equal volume of 6 randomly selected, individual plasmas (4 male and 2 female healthy, drug-free volunteers). Thirty subjects (20 females and 10 males) participated in this study. With the exception of fluvoxamine, this inhibitory effect was lacking in various other commonly used drugs with widely different chemical structures and pharmacological profiles, eg, antidepressants (SSRIs, imipramine-like tricyclics, MAOIs), acute antimigraine agents (triptan class drugs), the nonselective beta-adrenergic antagonist propranolol, and serotonin receptor agonists and antagonists. Agents (concentration 10 M used as illustration), listed in decreasing order of LEU-AP inhibitory activity: substance P > angiotensin III > methionine-enkephalin > angiotensin II > fluvoxamine > bestatin gave t1/2 values (+/- SD) of 39.3 +/- 1.1, 29.4 +/- 0.8, 28.3 +/- 0.8, 27.4 +/- 0.7, 24.5 +/- 1.5, and 23.6 +/- 0.9 minutes, respectively. Control, bacitracin, and fluphenazine (known LEU-AP inhibitors were used for comparison) values of 11.8 +/- 1.0, 31.3 +/- 0.7, and 19.6 +/- 1.0 minutes, respectively. As expected, these drugs significantly decreased the initial velocity of peptide degradation; Iv values (+/- SD) of: 0.17 +/- 0.1 (0.02 +/- 0.01), 0.23 +/- 0.2 (0.02 +/- 0.01), 0.25 +/- 0.2 (0.02 +/- 0.01), 0.26 +/- 0.2 (0.03 +/- 0.01), 0.31 +/- 0.1 (0.03 +/- 0.01), and 0.33 +/- 0.1 (0.03 +/- 0.01), respectively; control, bacitracin, and fluphenazine: 1.10 +/- 0.3 (0.12 +/- 0.03), 0.20 +/- 0.1 (0.02 +/- 0.01), and 0.82 +/- 0.2 (0.08 +/- 0.02) pg LEU/min (pg LEU/mg protein/min), respectively. Results emphasize the selective nature of chemical structures required to significantly inhibit AP activity and provided information that could help the rational design of agents with high specificity in a biologic milieu containing multiple peptidases. In this case, targeted modulation of the bioavailability of LEU and other endogenous AP-degraded hormonal and nonhormonal peptides could be useful in the treatment of the pathophysiology associated with various disease conditions. Whether their development could find useful pharmacological applications remains to be explored.

Comparative effects of rapid bolus administration of aqueous amiodarone versus 10-minute cordarone I.v. infusion on mean arterial blood pressure in conscious dogs.

OBJECTIVE: This study was designed to test the hypothesis that rapid bolus administration of an aqueous formulation of intravenous amiodarone causes less hypotension than a 10-minute infusion of the standard formulation, Cordarone IV. Hypotension was the most common adverse event reported with Cordarone IV. The hypotension was not dose related, but related to the rate of infusion. Therefore, product labeling calls Cordarone and its generic formulations to be administered over 10 minutes. Cordarone IV contains polysorbate 80 and benzyl alcohol, each causes hypotension. A new aqueous formulation of amiodarone (Amio-Aqueous) does not contain these agents and therefore may cause less hypotension. METHODS: Six conscious beagle dogs were instrumented with a telemetric device for blood pressure monitoring. The study was conducted on 5 days. On the first 2 days, a 10-min infusion or a bolus of D(5)W was administered (placebo). Over the following 3 days, the dogs received (in randomized order, one per day) a 10-min infusion of 2.5 mg/kg Cordarone IV and boluses of 2.5 mg/kg and 5.0 mg/kg Amio-Aqueous injected over 2 to 5 sec. The dogs were monitored for 2 hrs after dosing. RESULTS: Compared to placebo, boluses of aqueous amiodarone produced no significant changes in the mean arterial blood pressure (MABP). In contrast, Cordarone infusion produced significant decreases in MABP that lasted for at least 2 hrs (p < 0.001). CONCLUSION: Amio-Aqueous had significantly better hemodynamic profile permitting rapid intravenous administration. This is a significant advantage over the standard formulation, because Cordarone cannot be administered by rapid bolus due to excipient-related hypotension.

Rapid determination of partition coefficients between n-octanol/water for cardiovascular therapies.

The lipid solubility of a pharmaceutical may greatly influence its tissue activity. To evaluate lipid solubility of a group of cardiovascular agents a procedure to determine partition coefficients in n-octanol/water for a series of cardiovascular compounds was described. Ultraviolet absorbance measurements were used to assess partitioning between the two liquid phases of these compounds. In this study, sotalol was found to be the most hydrophilic (n-octanol/water ratio of 0.33) and fosinopril-sodium was the most lipophilic (ratio of 6.19). This is a versatile method permitting the evaluation of lipophilicity and, thus, parameters governing the events leading to pharmacologic actions such as gastrointestinal dissolution, absorption, and bioavailability. These observations can be related to a drug series, composed of several compounds having structural similarities or minor variations. The lipid solubility of a compound can markedly alter its side-effects profile, especially because lipophilic drugs enter the central nervous system with facility. Additionally, lipophilic agents may enter target tissue with greater ease than nonlipophilic compounds and thus possess local intracellular effects in addition to a macro systemic action.