Guillermo Di Girolamo

Mechanisms of Drug Induced QT Interval Prolongation

The long QT syndrome (LQTS) is characterized by a prolonged QT interval, as well as a propensity to develop syncope and sudden cardiac death caused by the malignant polymorphic ventricular arrhythmia called torsades de pointes (TdP). The QT interval is measured from the onset of the QRS complex to the end of the T wave and can be affected by both ventricular conduction velocities as well as by the velocity of repolarization. In most cases, QT prolongation is caused by factors that prolong the duration of the action potential, mainly by delaying the repolarization phase 3. The molecular mechanism is partially known. There are two well described mechanisms: blocking of the ion channel cavity of HERG; or causing an abnormal protein trafficking required for the location of HERG subunits in cell membrane. Both of them impair the I(Kr) current. However the blockade of ion channels is not the only condition to generate TdP. Other factors may play an important role, e.g. myocardium heterogeneity, drug-drug interaction, genetic polymorphism, and Electrolyte disturbances. Several drugs had been subject of withdrawal because QT-prolongation and arrhythmia. Understanding of processes involved in drug-induced QT prolongation is needed for the study and prevention of life-threatening arrhythmias.

Other Drugs Acting on Nervous System Associated with QT-Interval Prolongation

Several drugs acting on the nervous system have been implicated in the prolongation of the QT interval. Leaving aside the antidepressant and antipsychotic drugs, some have shown to prolong the QT interval in vivo. These include opioids, particularly methadone, inhalational anesthetics, and some preparations used for treatment of cough. These drugs have a narrow therapeutic interval or possible drug interactions that lead to clinical toxicity manifested by arrhythmias. They share the ability to block potassium channels (HERG), prolong the action potential and QT interval, and generate arrhythmias and Torsades de Pointes like other typicality recognized like antiarrhythmics, antihistamines, prokinetics, psychotropics and anti-infectives agents. Muscle relaxants like alcuronium, pancuronium and atracurium associated with or without atropine prolong significantly the QT interval. Methadone is the opiod most tightly associated with QTc prolongation; with much lesser potency buprenorphine and oxycodone can block HERG channels and depress the IKr current in vitro.Antineoplastic chemotherapy like anthracyclines, alkylating drugs, alkilants and cisplatin are associated with electrocardiographic alterations including prolongation of QT and emesis of different grades. Its very important take in account the synergic effects over the QT prolongation when effective antiemetics like 5-HT3 receptor antagonist (granisetron, ondansetron, and dolasetron) are administered. The Knowledge of their pharmacological properties is of vital importance to avoid exposing particularly vulnerable individuals as those with congenital long QT syndrome, and even the general public to unnecessary risk of potentially fatal arrhythmias.

Bioequivalence of two tablet formulations of clopidogrel in healthy argentinian volunteers: A single-dose, randomized-sequence, open-label crossover study

BACKGROUND Platelet activation is a major component in the pathogenesis of coronary thrombosis and myocardial infarction. Thienopyridines, particularly clopidogrel, are highly effective in reducing in-stent thrombosis and functional inhibition of adenosine diphosphate-induced platelet activation. OBJECTIVE The aim of this study was to evaluate the bioequivalence of a new generic formulation of clopidogrel 75-mg tablets (test) and the available branded formulation (reference) to meet regulatory criteria for marketing the test product in Argentina. METHODS This was a randomized-sequence, open-label, 2-period crossover study conducted in healthy white volunteers in the fasted state. A single oral dose of the test or reference formulation was followed by a 7-day washout period, after which subjects received the alternative formulation. Blood samples were collected at baseline and at 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 4, 6, 8, and 12 hours after dosing. Clopidogrel concentrations were determined using an LC-MS/MS method. The formulations were considered bioequivalent if the 90% CI of the geometric mean ratios (test:reference) for C(max) and AUC(0-last) were within the range from 80% to 125%. Adverse events were monitored throughout the study based on clinical parameters and patient reports. RESULTS Twenty-four volunteers (13 male, 11 female; mean [SD] age, 33.7 [5.2] years [range, 21-42 years]; weight, 72.4 [6.83] kg [range, 59-82 kg]) were enrolled in and completed the study. The geometric mean C(max) for the test and reference formulations was 877.76 and 913.49 pg/mL, respectively. The geometric mean AUC(0-t) was 1911.53 and 2053.09 pg . h/mL, and the geometric mean AUC(0-infinity)) was 2021.33 and 2188.25 pg . h/mL. The geometric mean ratios (test:reference) for C(max), AUC(0-t), and AUC(0-infinity)) were 96.09% (90% CI, 90.71-101.78), 93.10% (90% CI, 85.57-101.3), and 92.37% (90% CI, 85.06-100.31), respectively. There were no significant differences in pharmacokinetic parameters between groups. No adverse events were reported. CONCLUSION In this single-dose study in healthy fasted volunteers, the test formulation of clopidogrel tablets met the US and Argentinian regulatory criterion for bioequivalence to the reference formulation.

Beyond efficacy: pharmacokinetic differences between clopidogrel, prasugrel and ticagrelor

Introduction: Clinical nonresponse to clopidogrel has been associated with variability in response. This has led to the development of other P2Y12 receptor inhibitors, such as prasugrel and ticagrelor, with different pharmacokinetic characteristics that influence their pharmacodynamics. Areas covered: Clopidogrel response variability is attributable to its complex pharmacokinetics and is vulnerable to genetic polymorphisms in genes involved in absorption, metabolism and drug–drug interactions (i.e., proton pump inhibitors). Prasugrel which has a simpler metabolism, leading to greater bioavailability, seems to be less affected by genetic or drug–drug interactions and achieves a greater antiplatelet effect. Ticagrelor is the most novel compound approved with a simpler metabolism. Both prasugrel and ticagrelor reached their antiplatelet effect faster and to a much greater extent than clopidogrel. All these differences observed in kinetics explain, to some degree, the efficacy and safety profile observed in clinical trials for these molecules associated with other antiplatelet agents (aspirin, gpIIb/IIIa inhibitors) and anticoagulants. Expert opinion: Clopidogrel is still the best standard of care. However, the pharmacokinetic advantages of both prasugrel and ticagrelor allow clinicians to center patient management by selecting the best drug for the appropriate subject.

The Influence of Dehydroepiandrosterone on Early Pregnancy in Mice

The aim of the present report was to study the role of high levels of dehydroepiandrosterone (DHEA) on the ovarian function and embryonic resorption during early pregnancy in BALB/c mice. Pregnant animals were injected with DHEA following both the post-implantatory (DHEA-2) and peri-implantatory (DHEA-6) models. Morphological studies of implantation sites showed 40% of embryonic resorption in the DHEA-2 group while 100% of resorption was observed in the DHEA-6 group. Serum samples of both DHEA-2 and DHEA-6 groups showed higher estradiol levels and a lower progesterone concentration than those of control groups. Ovarian prostaglandin E levels after both DHEA-2 and DHEA-6 treatments increased when compared to control groups. The antioxidant metabolite glutathione diminished during both DHEA treatments. In summary, the data presented here suggest that DHEA treatment during early pregnancy modulates the ovarian function and is responsible for embryonic resorption with different degrees depending on when it is administered.

Investigational treatments for Type 2 diabetes mellitus: exenatide and liraglutide

Although a number of compounds are currently used to treat Type 2 diabetes mellitus, achieving a sustained glycaemic control over time is often not possible using oral antidiabetics. Endogenous incretins exhibit beneficial effects that could be useful for Type 2 diabetes mellitus treatment, such as stimulating insulin secretion during hyperglycaemia, improving β-cell mass and function, reducing glucagon secretion, delaying gastric emptying, reducing postprandial hyperglycaemia and diminishing body weight; however, their short half-life makes them unsuitable for treatment. Incretin mimetics such as liraglutide and exenatide were developed to overcome this limitation. This review discusses the effects of these compounds and their potential as a new class of antidiabetic agents.

Pharmacogenomics and adverse drug reactions: the case of statins

Introduction: The use of genomics to predict adverse drug reactions (ADRs) has been the subject of much research over the last decade. Concerns about the muscular safety of statins, a highly prescribed group of drugs, are partially related to their high exposure. Many studies have identified a variety of genetic markers related to statin-induced myopathy. However, only polymorphisms in the SLCO1B1 gene (which encodes the carrier responsible for the hepatic uptake of statins, which, in turn, contributes to the regulation of plasma levels of SLCO1B1) were strongly associated with statin-induced muscular adverse effects. These was found to be most prominent for simvastatin. The strength of these findings relies on the use of modern genetic approaches, such as well-designed, case-controlled and genome-wide association studies. Nevertheless, the clinical use of this information is far from known at present and needs to be evaluated. Areas covered: The links between genetic polymorphisms (i.e., SLCO1B1 gene) and statin-induced muscle ADRs and the methodological issues involved in the establishment of such an association are explored. Expert opinion: Despite there being a statin–gene association for myopathy, in the case of some statins the usefulness of this information still needs to be proven.

Non-invasive routes for insulin administration: current state and perspectives.

Diabetes mellitus is a chronic disease that usually requires multiple insulin injections to achieve adequate glycaemic control. This represents a major cause of reduced compliance to treatment. Consequently, other routes for insulin administration have been explored. During recent years, much progress in the development of inhaled insulin has been made. Inhaled insulin has shown favourable properties, such as a rapid onset of action, improved bioavailability and good tolerability; thereby providing satisfaction and ease of administration. However, long-term safety of inhaled insulin needs to be assessed, and the cost would be higher than injectable insulin. Nasal, oral and transdermal insulins are undergoing early phases of pharmacological development. The purpose of this review is to describe the latest developments in the area of non-invasive routes for insulin delivery.

Is acetaminophen, and its combination with pamabrom, an effective therapeutic option in primary dysmenorrhoea?

Primary dysmenorrhoea is the most frequent gynaecological condition, with a prevalence of 40 – 90% in women within the reproductive age. It is characterised by cyclic pelvic pain related to menstrual period, vomiting and headache. As prostaglandins and leukotrienes appear to be a major causative factor in this condition, NSAIDs are the first choice for treatment. Acetaminophen is an over-the-counter analgesic/antipyretic agent widely used in primary dysmenorrhoea as monotherapy or in combination. It has a weak inhibitory action on peripheral prostaglandin synthesis. Acetaminophen displays good gastrointestinal tolerance without any effect on haemostasis. Its combination with pamabrom, a mild diuretic agent, (Women´s Tylenol Menstrual Relief Caplets®, Midol Teen®) was approved by the FDA for use in this indication. Nevertheless, the available information concerning the efficacy of acetaminophen in primary dysmenorrhoea is limited and not conclusive with respect to other NSAIDs or even placebo. The clinical evidence regarding the association with pamabrom is even more scarce. Well-designed, randomised, controlled trials are required to demonstrate the efficacy of the combination of acetaminophen plus pamabrom in the treatment of primary dysmenorrhoea.

Nonresponders to clopidogrel: pharmacokinetics and interactions involved

Importance of the field: The use of clopidogrel and aspirin has become standard therapy in patients with acute coronary syndromes and stent implantation. However, concern arises because about 25% of subjects are nonresponders to clopidogrel. This nonresponsiveness is associated with a threefold increase in adverse outcomes. Clopidogrel resistance is multifactorial, but genetic polymorphisms in clopidogrels metabolic activation (e.g., cytochrome P450 2C19) and drug–drug interactions at this level (e.g., between proton pump inhibitors (PPIs) and clopidogrel) are both associated with decreased clopidogrel efficacy. Despite all PPIs being potent inhibitors of CYP2C19, evidence about their clinical impact is controversial. Areas covered in this review: Pharmacogenomic and pharmacokinetic aspects of clopidogrel nonresponsiveness were considered in detail. What the reader will gain: The reader will gain an exhaustive review of the current state of the controversial issues regarding genetic polymorphisms and drug–drug interactions affecting clopidogrel efficacy. Take home message: It is important to consider clopidogrel resistance in some patients and establish strategies to handle this problem (e.g., genotyping, platelet aggregability tests, new antiplatelet drugs). The combined use of PPIs and clopidogrel is at present regulated by the FDA and EMEA; however, the risk/benefit balance should be made for each patient individually.