Milan C. Richir

Low plasma concentrations of arginine and asymmetric dimethylarginine in premature infants with necrotizing enterocolitis

Several studies have described reduced plasma concentrations of arginine, the substrate for nitric oxide synthase (NOS) in infants with necrotizing enterocolitis (NEC). No information on the plasma concentrations of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) in patients with NEC is currently available. We investigated whether plasma concentrations of arginine, ADMA, and their ratio differ between premature infants with and without NEC, and between survivors and non-survivors within the NEC group. In a prospective case-control study, arginine and ADMA concentrations were measured in ten premature infants with NEC (median gestational age 193 d, birth weight 968 g), and ten matched control infants (median gestational age 201 d, birth weight 1102 g), who were admitted to the Neonatal Intensive Care Unit. In the premature infants with NEC, median arginine and ADMA concentrations (micromol/l), and the arginine:ADMA ratio were lower compared to the infants without NEC: 21.4 v. 55.9, P= 0.001; 0.59 v. 0.85, P=0.009 and 36.6 v. 72.3, P=0.023 respectively. In the NEC group, median arginine (micromol/l) and the arginine:ADMA ratio were lower in non-surviving infants than in surviving infants: 14.7 v. 33.8, P=0.01 and 32.0 v. 47.5, P=0.038 respectively. In premature infants with NEC not only the NOS substrate arginine, but also the endogenous NOS inhibitor ADMA and the arginine:ADMA ratio were lower than in infants without NEC. In addition, low arginine and arginine:ADMA were associated with mortality in infants with NEC. Overall, these data suggest that a diminished nitric oxide production may be involved in the pathophysiology of NEC, but this needs further investigation.

Teaching clinical pharmacology and therapeutics with an emphasis on the therapeutic reasoning of undergraduate medical students

BackgroundThe rational prescribing of drugs is an essential skill of medical doctors. Clinical pharmacologists play an important role in the development of these skills by teaching clinical pharmacology and therapeutics (CP&T) to undergraduate medical students. Although the approaches to teaching CP&T have undergone many changes over the last decennia, it is essential that the actual teaching of CP&T continues to be a major part of the undergraduate medical curriculum.ObjectivesThe learning objectives of CP&T teaching in terms of developing the therapeutic competencies of undergraduate medical students are described, with an emphasis on therapeutic decision-making. On the basis of current theories of cognitive psychology and medical education, context-learning is presented as an effective approach by which to achieve therapeutic competencies. An example of a CP&T curriculum is presented.

Imbalance of arginine and asymmetric dimethylarginine is associated with markers of circulatory failure, organ failure and mortality in shock patients

In shock, organ perfusion is of vital importance because organ oxygenation is at risk. NO, the main endothelial-derived vasodilator, is crucial for organ perfusion and coronary patency. The availability of NO might depend on the balance between a substrate (arginine) and an inhibitor (asymmetric dimethylarginine; ADMA) of NO synthase. Therefore, we investigated the relationship of arginine, ADMA and their ratio with circulatory markers, disease severity, organ failure and mortality in shock patients. In forty-four patients with shock (cardiogenic n 17, septic n 27), we prospectively measured plasma arginine and ADMA at intensive care unit admission, Acute Physiology and Chronic Health Evaluation (APACHE) II-(predicted mortality) and Sequential Organ Failure Assessment (SOFA) score, and circulatory markers to investigate their relationship. Arginine concentration was decreased (34·6 (SD 17·9) μmol/l) while ADMA concentration was within the normal range (0·46 (SD 0·18) μmol/l), resulting in a decrease in the arginine:ADMA ratio. The ratio correlated with several circulatory markers (cardiac index, disseminated intravascular coagulation, bicarbonate, lactate and pH), APACHE II and SOFA score, creatine kinase and glucose. The arginine:ADMA ratio showed an association (OR 0·976, 95 % CI 0·963, 0·997, P = 0·025) and a diagnostic accuracy (area under the curve 0·721, 95 % CI 0·560, 0·882, P = 0·016) for hospital mortality, whereas the arginine or ADMA concentration alone or APACHE II-predicted mortality failed to do so. In conclusion, in shock patients, the imbalance of arginine and ADMA is related to circulatory failure, organ failure and disease severity, and predicts mortality. We propose a pathophysiological mechanism in shock: the imbalance of arginine and ADMA contributes to endothelial and cardiac dysfunction resulting in poor organ perfusion and organ failure, thereby increasing the risk of death.

Should medical students learn to develop a personal formulary? An international, multicentre, randomised controlled study

ObjectiveThis study was performed to determine whether students who are trained in developing a personal formulary become more competent in rational prescribing than students who have only learned to use existing formularies.MethodsThis was a multicentre, randomised, controlled study conducted in eight universities in India, Indonesia, the Netherlands, the Russian Federation, Slovakia, South Africa, Spain and Yemen. Five hundred and eighty-three medical students were randomised into three groups: the personal formulary group (PF; 94), the existing formulary group (EF; 98) and the control group (C; 191). The PF group was taught how to develop and use a personal formulary, whereas e the EF group was taught how to review and use an existing formulary. The C group received no additional training and participated only in the tests. Student’s prescribing skills were measured by scoring their treatment plans for written patient cases.ResultsThe mean PF group score increased by 23% compared with 19% for the EF group (p < 0.05) and 6% for controls (p < 0.05). The positive effect of PF training was only significant in universities that had a mainly classic curriculum.ConclusionTraining in development and use of a personal formulary was particularly effective in universities with a classic curriculum and with traditional pharmacology teaching. In universities with a general problem-based curriculum, pharmacotherapy teaching can be based on either existing or personal formularies.

A Context‐Learning Pharmacotherapy Program for Preclinical Medical Students Leads to More Rational Drug Prescribing During Their Clinical Clerkship in Internal Medicine

The irrational prescribing of drugs seems to be a general problem in medical practice, occasionally leading to serious consequences. In order to improve the drug prescribing performance of medical students, a compulsory context‐learning pharmacotherapy module was implemented in 1998 in the medical curriculum of 2nd–4th‐year medical students at the VU University Medical Center (VUmc), Amsterdam, the Netherlands. As part of this program, preclinical medical students are taught how to select, prescribe, and evaluate a drug regimen rationally. The aim of this study was to investigate the effect of this preclinical pharmacotherapy program on the quality of rational prescribing during the ensuing clinical clerkship of these students in internal medicine. The results of this study indicate that preclinical context‐learning in pharmacotherapy leads to the use of more rational prescribing modalities by medical students during their ensuing clinical clerkship in internal medicine. This effect was obtained not only with respect to the clinical topics in which training had been given as part of the pharmacotherapy curriculum, but also for other disease situations that the students dealt with. This implies that students not only remember the specific information they have learned during the training, but are also able to apply the acquired skills in new situations (transfer effect).

The Prominent Role of the Liver in the Elimination of Asymmetric Dimethylarginine (ADMA) and the Consequences of Impaired Hepatic Function

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS), the enzyme which converts the amino acid arginine into nitric oxide (NO). ADMA has been identified as an important risk factor for cardiovascular diseases. Besides the role of ADMA in cardiovascular diseases, it also seems to be an important determinant in the development of critical illness, (multiple) organ failure, and the hepatorenal syndrome. ADMA is eliminated from the body by urinary excretion, but it is mainly metabolized by the dimethylarginine dimethylaminohydrolase (DDAH) enzymes that convert ADMA into citrulline and dimethylamine. DDAH is highly expressed in the liver, which makes the liver a key organ in the regulation of the plasma ADMA concentration. The prominent role of the liver in the elimination of ADMA and the consequences of impaired hepatic function on ADMA levels will be discussed in this article.

No Compensatory Upregulation of Placental Dimethylarginine Dimethylaminohydrolase Activity in Preeclampsia

Background/Aims: Placental dysfunction of the asymmetric dimethylarginine (ADMA) degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH) has been suggested as one of the initiating events in the development of preeclampsia (PE). Our primary aim was to investigate the role of the placenta in the metabolism of ADMA during normal pregnancy and PE. Methods: We studied 27 nonpregnant healthy women (C), 15 normotensive pregnant females (P), 16 patients with PE, and 7 patients with the ‘hemolysis, elevated liver enzymes and low platelets’ syndrome (H). Results: There were no significant differences between P and PE with respect to fetomaternal gradient of ADMA, placental DDAH activity and placental ADMA content. During the first stage of labour, mean (±SD) plasma ADMA (μmol/l) was higher in H (0.69 ± 0.22; p < 0.05) compared with C (0.44 ± 0.07), P (0.37 ± 0.06), and PE (0.40 ± 0.06). ADMA was significantly associated with laboratory parameters of hepatic and renal function and with clinical parameters, including systolic and diastolic blood pressure, gestational age, birth weight, and placenta weight. Conclusions: A compensatory upregulation of placental DDAH activity is absent in patients suffering from PE and levels of ADMA in plasma and placenta are normal in patients suffering from PE. However, when the course of PE deteriorates and organ dysfunction (especially liver and kidney) becomes involved, such as during the hemolysis, elevated liver enzymes and low platelets syndrome, ADMA levels increase.

Low arginine/asymmetric dimethylarginine ratio deteriorates systemic hemodynamics and organ blood flow in a rat model

Objective:Both arginine and asymmetric dimethylarginine (ADMA) play a crucial role in the arginine–nitric oxide pathway. Low arginine and high ADMA levels can be found in critically ill patients after major surgery. The aim of this study was to evaluate the effects of low arginine plasma concentrations in combination with high ADMA plasma concentrations on hemodynamics and organ blood flow. Design:Randomized, placebo-controlled animal laboratory investigation. Subjects:Male Wistar rats (n = 21), anesthetized. Interventions:Rats were randomly assigned to three groups: a control group, an ADMA group, or an arginase (ASE)/ADMA group. In the control group, rats received (at t = 0) an intravenous (IV) infusion of 1.5 mL 0.9% NaCl during a 20-minute period. After 60 minutes (t = 60), rats received an IV bolus of 1.0 mL 0.9% NaCl. In the ADMA group, rats received an IV infusion of 1.5 mL 0.9% NaCl during a 20-minute period and at t = 60 an IV bolus of 1.0 mL ADMA (20 mg/kg). In the ASE/ADMA group, rats received an IV infusion of 1.5 mL ASE (3200 IU) solution during a 20-minute period and at t = 60 an IV bolus of 1.0 mL ADMA (20 mg/kg). Measurements and Main Results:Infusion of ADMA (20 mg/kg) and ASE (3200 IU) resulted in increased plasma ADMA levels and decreased arginine levels. During the whole experiment, systemic hemodynamics (heart rate, mean arterial pressure [MAP], and cardiac output) were measured. In addition, organ blood flow was measured at t = 90 and t = 180 minutes, using fluorescent microspheres. Compared with the control group, MAP and systemic vascular resistance were increased after infusion of ADMA. Infusion of ASE in combination with ADMA significantly deteriorated systemic hemodynamics (MAP, cardiac output, stroke volume, and systemic vascular resistance) and organ blood flow through the kidney and spleen. In addition, an initial decrease in arterial flow, followed by a later major increase, and panlobular apoptosis and necrosis of the liver was observed. Conclusions:The current study shows that low arginine plasma levels in combination with high ADMA plasma levels deteriorates systemic hemodynamics and reduces blood flow through the kidney and spleen and liver. These data suggest that a diminished nitric oxide production may be involved in the onset of organ failure.

Role of dimethylarginine dimethylaminohydrolase activity in regulation of tissue and plasma concentrations of asymmetric dimethylarginine in an animal model of prolonged critical illness

High plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with adverse outcome in critically ill patients. Asymmetric dimethylarginine is released within cells during proteolysis of methylated proteins and is either degraded by dimethylarginine dimethylaminohydrolase (DDAH) or exported to the circulation via cationic amino acid transporters. We aimed to establish the role of DDAH activity in the regulation of tissue and plasma concentrations of ADMA. In 33 critically ill rabbits, we measured DDAH activity in kidney, liver, heart, and skeletal muscle and related these values to concentrations of ADMA in these tissues and in the circulation. Both DDAH activity and ADMA concentration were highest in kidney and lowest in skeletal muscle, with intermediate values for liver and heart. Whereas ADMA content was significantly correlated between tissues (r = 0.40-0.78), DDAH activity was not. Significant inverse associations between DDAH activity and ADMA content were only observed in heart and liver. Plasma ADMA was significantly associated with ADMA in the liver (r = 0.41), but not in the other tissues. In a multivariable regression model, DDAH activities in muscle, kidney, and liver, but not in heart, were negatively associated with plasma ADMA concentration, together explaining approximately 50% of its variation. In critical illness, plasma ADMA poorly reflects intracellular ADMA. Furthermore, tissue DDAH activity is a stronger predictor of plasma ADMA than of intracellular ADMA, indicating that, compared with DDAH activity, generation of ADMA and cationic amino acid transporter-mediated exchange may be more important regulators of intracellular ADMA.

Do medical students copy the drug treatment choices of their teachers or do they think for themselves

PurposeAlthough the importance of rational prescribing is generally accepted, the teaching of pharmacotherapy to undergraduate medical students is still unsatisfactory. Because clinical teachers are an important role model for medical students, it is of interest to know whether this extends to therapeutic decision-making. The aim of this study was to find out which factors contribute to the drug choices made by medical students and their teachers (general practitioners and clinical specialists).MethodsFinal-year medical students (n = 32), and general practitioners (n = 29), lung specialists (n = 26), orthopaedic surgeons (n = 24), and internists (n = 24) serving as medical teachers from all eight medical schools in the Netherlands participated in the study. They were asked to prescribe treatment (drug or otherwise) for uncomplicated (A) and complicated (B) written patient cases and to indicate which factors influenced their choice of treatment, using a list of factors reported in the literature to influence drug prescribing.ResultsFinal-year medical students primarily based their drug choice on the factors ‘effectiveness of the drugs’ and ‘examples from medical teachers’. In contrast, clinical teachers primarily based their drug choice on the factors ‘clinical experience’, ‘effectiveness of the drugs’, ‘side effects of the drugs’, ‘standard treatment guidelines’, and ‘scientific literature’.ConclusionsMedical teachers would appear to base their drug choice mainly on clinical experience and drug-related factors, whereas final-year medical students base their drug choice mainly on examples provided by their medical teachers. It is essential that medical teachers clearly explain to their students how they arrive at a specific choice of medication since medical students tend to copy the therapeutic drug choices from their teachers, mainly because of a lack of experience. Presenting students with clinical therapeutic problems early during undergraduate training will not only give them a chance to gain experience in solving medical problems but will also give meaning to what they are studying as opposed to merely reproducing what they learn or copying what they are told.