Update on Cilostazol: A Critical Review of Its Antithrombotic and Cardiovascular Actions and Its Clinical Applications.

Cilostazol, a phosphodiesterase III inhibitor, has vasodilating and antiplatelet properties with a low rate of bleeding complications. It has been used over the past 25 years for improving intermittent claudication in patients with peripheral artery disease (PAD). Cilostazol also has demonstrated efficacy in patients undergoing percutaneous revascularization procedures for both PAD and coronary artery disease. In addition to its antithrombotic and vasodilating actions, cilostazol also inhibits vascular smooth muscle cell proliferation via phosphodiesterase III inhibition, thus mitigating restenosis. Accumulated evidence has shown that cilostazol, due to its "pleiotropic" effects, is a useful, albeit underutilized, agent for both coronary artery disease and PAD. It is also potentially useful after ischemic stroke and is an alternative in those who are allergic or intolerant to classical antithrombotic agents (eg, aspirin or clopidogrel). These issues are herein reviewed together with the pharmacology and pharmacodynamics of cilostazol. Large studies and meta-analyses are presented and evaluated. Current guidelines are also discussed, and the spectrum of cilostazol's actions and therapeutic applications are illustrated.

Developmental Pharmacokinetics and Age-Appropriate Dosing Design of Milrinone in Neonates and Infants with Acute Kidney Injury Following Cardiac Surgery.

BACKGROUND AND OBJECTIVE: Milrinone is used for the prevention of low cardiac output syndrome in pediatric patients after cardiac surgery. Milrinone is mainly eliminated by the kidneys; however, there is limited information on milrinone pharmacokinetics in infants who have acute kidney injury (AKI). The aim of this study was to develop a milrinone population pharmacokinetic model in neonates and infants with or without AKI. The developed milrinone pharmacokinetic model was utilized for a Monte Carlo simulation analysis to identify age-appropriate dosing regimens in neonates and infants. METHODS: Population pharmacokinetic analysis was performed with a total of 1088 serum milrinone concentrations obtained from 92 infants as part of a prospective clinical study in neonates and infants following cardiac surgery (ClinicalTrials.gov identifier NCT01966237). AKI stages were determined based on the Kidney Injury Improving Global Outcomes (KDIGO) Clinical Practice Guideline within the first three postoperative days. RESULTS: A two-compartment model was found to adequately describe the pharmacokinetic data. Allometrically scaled body weight, AKI stages, and maturation function were identified as significant predictors of milrinone clearance. The proposed dosing regimens for milrinone continuous infusions were determined based on a target concentration attainment of simulated steady-state concentration and covered three age groups across 0-12 months of age for each AKI stage. CONCLUSION: This study provides a milrinone population pharmacokinetic model in neonates and infants and captures the developmental changes in clearance. Age-appropriate dosing regimens were determined based on the simulation analysis with the developed pharmacokinetic model. The findings will facilitate model-informed precision dosing of milrinone in infants with or without AKI.

Effects of CYP2C19 and CYP3A5 genetic polymorphisms on the pharmacokinetics of cilostazol and its active metabolites.

PURPOSE: CYP3A4, CYP2C19, and CYP3A5 are primarily involved in the metabolism of cilostazol. We investigated the effects of CYP2C19 and CYP3A5 genetic polymorphisms on the pharmacokinetics of cilostazol and its two active metabolites. METHODS: Thirty-three healthy Korean volunteers were administered a single 100-mg oral dose of cilostazol. The concentrations of cilostazol and its active metabolites (OPC-13015 and OPC-13213) in the plasma were determined by HPLC-MS/MS. RESULTS: Although the pharmacokinetic parameters for cilostazol were similar in different CYP2C19 and CYP3A5 genotypes, CYP2C19PM subjects showed significantly higher AUC0-∞ for OPC-13015 and lower for OPC-13213 compared to those in CYP2C19EM subjects (P < 0.01 and P < 0.001, respectively). Pharmacokinetic differences in OPC-13015 between CYP3A5 non-expressors and expressors were significant only within CYP2C19PM subjects. The amount of cilostazol potency-adjusted total active moiety was the greatest in subjects with CYP2C19PM-CYP3A5 non-expressor genotype. CONCLUSION: These results suggest that CYP2C19 and CYP3A5 genetic polymorphisms affect the plasma exposure of cilostazol total active moiety. CYP2C19 plays a crucial role in the biotransformation of cilostazol.

Comparative Fasting Bioavailability of 2 Cilostazol Formulations in Healthy Thai Volunteers: An Open-Label, Single-Dose, Randomized, 2-Way Crossover Study.

OBJECTIVE: To evaluate the bioequivalence of50 mg cilostazol tablets manufactured locally (Citazol®) and originally (Pletaal®) in healthy Thai volunteers. MATERIAL AND METHOD: An open-label, single dose, randomized, two-period, two-sequence, crossover study in 30 healthy volunteers. Each volunteer received a 50 mg cilostazol tablet of bothformulations with a washoutperiodofat least 14 days. Blood samples were obtained atpre-dose and over 48 hours after dosing. Cilostazolplasma concentrations were quantified by using liquid chromatography with tandem mass spectrometry (LC-MS/MS). RESULTS: The 30 volunteers completed the entire study. The geometric mean ratios (GAM) (test/reference) between the two formulations of cilostazol were 112.38% (101.70%-124.19%) for Cmax; 103.66% (96.06%-111.86%) for AUC0-48; and 95.14% (86.12%-105.12%)forAUC0-∞. There was no statistical difference ofthe Tmax between the twoformulations (p>0.05). No serious adverse events related to the studied drugs were found. CONCLUSION: No significant difference in the analyzed pharmacokineticparameters was found between the twoformulations of 50 mg cilostazol tablets. Therefore, it can be concluded that these two cilostazol tablet formulations were considered bioequivalent.

Preparation and characterization of microemulsion of cilostazol for enhancement of oral bioavailability.

Cilostazol is a promising drug for antiplatelet combination therapy that is very important for treatment for various cardiovascular disorders. However, oral delivery of this drug is greatly impeded by the poor solubility in aqueous solutions. The aim of this study was to develop microemulsion (ME) delivery system capable of improving the drug bioavailability. In this study, Capmul MCM C8 (glycerol monocaprylate) based MEs containing Tween 20(polysorbate 20) and/or Labrafil M 1944(poly oxyglycerides) as surfactant(S) and Transcutol P(diethyl glycol monoethyl ether) as cosurfactant(CoS) were studied as potential delivery systems of cilostazol. A number of such systems were prepared containing different S:CoS ratios(1:1, 2:1 and 3:1) based on phase diagrams. Loading of cilostazol was selected as per solubilization capacity and was characterized for pH, viscosity, conductivity, particle size, zeta potential and % transmittance. The MEs systems were further investigated for chemical stability, diffusion and bioavailability. Cilostazol displayed high solubility in microemulsions with particle size up to 70 nm. It was also stable at ambient temperature up to 6 months without significant change in particle size, zeta potential, and % transmittance. Dilution up to 100 fold with aqueous medium observed a visible cloudiness having a particle size up to 104 nm. The in vitro release, and ex vivo intraduodenal diffusion, and in vivo study indicated the capacity of developed ME to improve the bioavailability (1.43 fold) via oral route administration when compared with commercially available tablets (Pletoz-50).

Method development and validation of olprinone in human plasma by HPLC coupled with ESI-MS-MS: application to a pharmacokinetic study.

A simple, specific and highly sensitive assay using liquid chromatography-tandem mass spectrometry with electrospray ionization was developed for the determination of olprinone in human plasma. Following the addition of codeine as an internal standard and simple liquid-liquid extraction with ethyl acetate-isopropanol (95:5, v/v), the analytes were separated on a Zorbax SB-C18 column (4.6 × 150 mm i.d., 5 µm) and eluted with a mobile phase consisting of methanol-10 mmol/L ammonium acetate containing 1% formic acid (50:50, v/v) at a flow rate of 1.0 mL/min. Detection was achieved with electrospray positive ionization mass spectrometry using multiple reaction monitoring mode. Linear calibration curves were obtained in the concentration range of 0.1-100 ng/mL (r = 0.9995), with a lower limit of quantification of 0.1 ng/mL. The intra-day and inter-day precision values, as relative deviation, were below 6.06% and the accuracy, as relative error, was below 9.92% at all quality control concentrations. The method was applicable to clinical pharmacokinetic study of an olprinone hydrochloride hydrate injection in healthy Chinese volunteers.

Pharmacology of milrinone in neonates with persistent pulmonary hypertension of the newborn and suboptimal response to inhaled nitric oxide.

OBJECTIVES: Persistent pulmonary hypertension of the newborn is a common problem with significant morbidity and mortality. Inhaled nitric oxide is the standard care, but up to 40% of neonates are nonresponders. Milrinone is a phosphodiesterase III inhibitor which increases the bioavailability of cyclic adenosine monophosphate and has been shown to improve pulmonary hemodynamics in animal experimental models. The primary objective was to investigate the pharmacological profile of milrinone in persistent pulmonary hypertension of the newborn. Secondary objectives were to delineate short-term outcomes and safety profile. SUBJECTS AND METHODS: An open label study of milrinone in neonates with persistent pulmonary hypertension of the newborn was conducted. Patients received an intravenous loading dose of milrinone (50 µg/kg) over 60 mins followed by a maintenance infusion (0.33-0.99 µg/kg/min) for 24-72 hrs. Physiologic indices of cardiorespiratory stability and details of cointerventions were recorded. Serial blood milrinone levels were collected after the bolus, following initiation of the maintenance infusion to determine steady state levels, and following discontinuation of the drug to determine clearance. Echocardiography was performed before and after (1, 12 hrs) milrinone initiation. INTERVENTIONS: Milrinone. MEASUREMENTS AND MAIN RESULTS: Eleven neonates with a diagnosis of persistent pulmonary hypertension of the newborn who met eligibility criteria were studied. The median (SD) gestational age and weight at birth were 39.2 ± 1.3 wks and 3481 ± 603 g. The mean (± sd) half-life, total body clearance, volume of distribution, and steady state concentration of milrinone were 4.1 ± 1.1 hrs, 0.11 ± 0.01 L/kg/hr, 0.56 ± 0.19 L/kg, and 290.9 ± 77.7 ng/mL. The initiation of milrinone led to an improvement in PaO2 (p = 0.002) and a sustained reduction in FIO2 (p < 0.001), oxygenation index (p < 0.001), mean airway pressure (p = 0.03), and inhaled nitric oxide dose (p < 0.001). Although a transient reduction in systolic arterial pressure (p < 0.001) was seen following the bolus, there was overall improvement in base deficit (p = 0.01) and plasma lactate (p = 0.04) with a trend towards lower inotrope score. Serial echocardiography revealed lower pulmonary artery pressure, improved right and left ventricular output, and reduced bidirectional or right-left shunting (p < 0.05) after milrinone treatment. CONCLUSIONS: The pharmacokinetics of milrinone in persistent pulmonary hypertension of the newborn is consistent with published data. The administration of intravenous milrinone led to better oxygenation and improvements in pulmonary and systemic hemodynamics in patients with suboptimal response to inhaled nitric oxide. These data support the need for a randomized controlled trial in neonates.

The effect of hemodilution by cardiopulmonary bypass on protein binding of olprinone.

PURPOSE: Olprinone is a phosphodiesterase type III inhibitor that is often used to increase cardiac output after cardiopulmonary bypass (CPB). Hemodilution by CPB is likely to decrease total olprinone concentration, but it may also increase the free (unbound) concentration of olprinone due to reduced protein binding. The aim of this study was to investigate the effect of hemodilution on the protein binding of olprinone. METHODS: Eleven patients scheduled for elective cardiac surgery with CPB were enrolled in our study. Olprinone was continuously infused at a rate of 0.2 µg/kg/min from the time of the first surgical incision until the patient arrived at the recovery unit. Protein binding was evaluated twice, just before the start of CPB and at the beginning of withdrawal from CPB. Olprinone concentration and protein binding were determined with high-performance liquid chromatography and ultrafiltration methods, respectively. Olprinone protein binding was also evaluated in vitro. RESULTS: Olprinone protein binding to albumin was 63 % in vitro, but it did not bind to alpha-1 acid glycoprotein. Olprinone protein binding in patients before CPB was 81.5 ± 4.3 %, whereas protein binding at withdrawal from CPB was 63.3 ± 14.3 %. CONCLUSIONS: Unbound olprinone concentration increased by 20 % during CPB, which suggests that the pharmacological effects of olprinone might be enhanced during and after CPB. Close hemodynamic monitoring is necessary to control the effects of olprinone after CPB, because CPB alters olprinone's pharmacokinetics.

Use of cilostazol in percutaneous coronary interventions.

OBJECTIVE: To evaluate the addition of cilostazol to standard dual antiplatelet therapy (DAT) with aspirin and clopidogrel in patients receiving coronary stenting. DATA SOURCES: Relevant information was identified through a search of MEDLINE (1966-November 2011), International Pharmaceutical Abstracts (1960-2011), and Cochrane Databases (publications archived until November 2011) using the terms cilostazol, percutaneous coronary intervention, triple therapy, and antiplatelet agents. STUDY SELECTION AND DATA EXTRACTION: English-language prospective and retrospective studies, including registry data in adults, were eligible for inclusion if triple therapy with cilostazol was compared with DAT with aspirin and clopidogrel in patients undergoing percutaneous coronary intervention (PCI) with stenting. Article bibliographies were also reviewed. DATA SYNTHESIS: Cilostazol uniquely possesses antiproliferative properties in addition to its antiplatelet effects. Several prospective and retrospective clinical trials evaluated it as a third agent in standard antiplatelet regimens after PCI with both bare metal and drug-eluting stents. Both angiographic and clinical outcomes, including major adverse cardiac events (MACEs), have been improved with the addition of cilostazol to DAT in most trials, without increasing bleeding risk. Higher-risk patients, such as elderly individuals and patients with diabetes, long lesions, or small vessels, seem to benefit the most from triple therapy. Patients who are poor responders to clopidogrel also appear to benefit from the addition of cilostazol by improving platelet reactivity with standard DAT. CONCLUSIONS: Triple therapy with cilostazol has been shown to reduce MACEs by providing increased inhibition of platelet aggregation and reducing the rates of in-stent thrombosis compared to DAT without increasing the risk of bleeding complications. Further studies are needed to identify proper patient selection based on risk factors for the addition of cilostazol. Additionally, studies comparing cilostazol with newer antiplatelet therapies, such as prasugrel and ticagrelor, are needed.

A phosphodiesterase 3 inhibitor, K-134, improves hindlimb skeletal muscle circulation in rat models of peripheral arterial disease.

OBJECTIVE: Cilostazol is a phosphodiesterase (PDE)3 inhibitor used to treat peripheral arterial disease with intermittent claudication, as there is clinical evidence that it improves treadmill exercise capacity. However, details of the mechanism underlying this enhanced walking capacity remain to be elucidated. METHODS: Based on the hypothesis that PDE3 inhibitors improve peripheral microcirculation in the hindlimbs via vascular smooth muscle relaxation and antiplatelet effects, we examined the effects of a more potent and selective PDE3 inhibitor, K-134, in rat models of peripheral arterial disease (PAD). RESULTS: In a hindlimb ischemia model established by bilateral femoral artery occlusion, oral administration of K-134 for 27 days significantly increased blood flow in hindlimb skeletal muscle after exercise induced by electrical stimulation of the sciatic nerve. Moreover, K-134 enlarged the luminal area of intramuscular arteries and prevented rarefaction of capillary density in the gastrocnemius muscle. These effects were observed without pre-administration on the day following the last administration, suggesting that vasodilatory, antiplatelet and angiogenic activities of K-134 were indirectly responsible for the long-term beneficial effects. In fact, K-134 dose-dependently induced relaxation of rat femoral arteries in vitro, and inhibited rat platelet aggregation ex vivo. Interestingly, in a laurate-induced peripheral vascular injury model, oral administration of K-134 for 6 days prevented progression of hindlimb necrosis. CONCLUSION: These findings suggest that the beneficial effects of PDE3 inhibitors on walking capacity are due to increased hindlimb skeletal muscle blood flow via intramuscular artery enlargement, and that K-134 is a promising drug for PAD associated with platelet hyperaggregability.

Determination of olprinone in human plasma utilizing liquid chromatography tandem mass spectrometry.

A sensitive and rapid method was developed for quantification of olprinone in human plasma utilizing liquid chromatography tandem mass spectrometry (LC-MS/MS). An aliquot of 1 mL plasma sample was extracted with ethyl acetate-dichloromethane. Separation of olprinone and the milrinone (internal standard, IS) from the interferences was achieved on a C(18) column followed by MS/MS detection. The analytes were monitored in the positive ionization mode. Multiple reaction monitoring using the transition of m/z 251 → m/z 155 and m/z 212 → m/z 140 was performed to quantify olprinone and IS, respectively. The method had a total chromatographic run time of 3 min and linear calibration curves over the concentration range of 0.5-60 ng/mL. The lower limit of quantification (LLOQ) was 0.5 ng/mL. The intra- and inter-day precisions were less than 16.3% for low QC level, and 7.1% for other QC levels, respectively. The intra- and inter-day relative errors were ranged between -12.2% and 3.7% for three QC concentration levels. The validated method was successfully applied to the quantification of olprinone concentration in human plasma after intravenous (i.v.) administration of olprinone at a constant rate of infusion of 2 µg/(kg min) for 5 min in order to evaluate the pharmacokinetics.