Michal Rotenberg

Interindividual variability in sensitivity to warfarin‐Nature or nurture?

Interindividual variability in responses to warfarin is attributed to dietary vitamin K, drug interactions, age, or genetic polymorphism in the cytochrome P4502C9 enzyme (CYP2C9) (allelic variants 2C9*2 and 2C9*3) linked with impaired metabolism of the potent enantiomere S ‐warfarin.

Differentiation between organophosphate and carbamate poisoning

We propose a novel and simple assay for the real-time differentiation between carbamate and organophosphate inhibition of cholinesterase, based on our observations of the kinetic behavior of inhibited enzyme. The assay of carbamylated cholinesterase activity over time follows a non-linear kinetic pattern, whereas that of phosphorylated enzyme activity is linear. This feature can be exploited to differentiate between carbamate and organophosphate cholinesterase inhibition. The non-linear pattern characteristic of carbamates is easily discernible at degrees of inhibition of 40% or more. In this setting, cholinesterase activity ought to be measured continuously for about 1 h to obtain the kinetic pattern of enzyme activity. The initial activity, measured during the first 5 min of assay, represents the activity of enzyme in vivo. In vitro reactivation of inhibited cholinesterase allows the estimation of full potential activity of enzyme prior to poisoning, so that percentage of inhibition can be calculated. Reactivation of carbamylated cholinesterase is obtained by the incubation of diluted enzyme at 37 degrees C for 2.5 h prior to assay, whereas phosphorylated (non-aged) enzyme is reactivated by a 30 min incubation with oximes. In cases of mild exposure to cholinesterase inhibitors (< 40% inhibition), the response of enzyme to in vitro reactivation serves as a complementary test for exposure and for the nature of the inhibitor. All the results presented in this work refer to plasma cholinesterase. Erythrocyte cholinesterase was found to behave very similarly to plasma enzyme and its results have not been reported here.

The pharmacokinetics of morphine and lidocaine in critically ill patients.

Objective: To evaluate the pharmacokinetic parameters of morphine and lidocaine after a single intravenous dose in critically ill patients. Design: Prospective, clinical study. Setting: General intensive care unit (ICU) in a university hospital. Patients: Patients admitted to the ICU with severe systemic inflammatory response syndrome of various etiologies. Interventions: A single intravenous dose of morphine (0.025 mg/kg) and lidocaine (1.5 mg/kg) were given separately 12–36 h after admission, and arterial blood samples for serum drug levels were taken. Measurements and results: Morphine pharmacokinetics were studied in 30 patients. The clearance (Cl) was found to be 5.7 ± 2.3 ml/kg per min, volume of distribution of the central compartment (Vc) 0.16 ± 0.12 l/kg and volume of distribution at steady state (Vss) 1.08 ± 0.69 l/kg. These values are lower then those described previously for healthy volunteers (33.5 ± 9 ml/kg per min, 1.01 ± 0.31 l/kg, and 5.16 ± 1.4 l/kg, respectively), and similar to those described in trauma and burned patients. Lidocaine pharmacokinetics were tested in 24 subjects. The Cl was 6.9 ± 3.8 ml/kg per min, Vc 0.25 ± 0.1 l/kg and Vss 0.78 ± 0.26 l/kg. These values are not different from parameters published previously for healthy volunteers (10 ml/kg per min, 0.53 l/min and 1.32 l/min, respectively). No correlation was found between clinical variables and pharmacokinetic parameters of both drugs (ANOVA). Conclusions: Both morphine and lidocaine have a reduced volume of distribution in critically ill patients. The normal lidocaine clearance indicates preserved hepatic blood flow and suggests that other mechanisms are involved in the reduced morphine clearance. These findings may have application for the treatment of ICU patients.

Effect of Azathioprine on the Anticoagulant Activity of Warfarin

TO THE EDITOR: Oral sulfonylurea antidiabetic drugs such as glyburide1 and chlorpropamide2 , 3 are known to induce thrombocytopenia. George et a l .4 recently reviewed published reports of drug-induced thrombocytopenia and proposed criteria to evaluate the level of evidence for a causal relationship of each drug to thrombocytopenia. We report a patient who developed thrombocytopenia after glimepiride treatment. According to the criteria developed by George et al., our observations support the existence of a causal relationship between glimepiride and thrombocytopenia. Case Report. A 68-year-old white man was referred to our hospital on April 21, 1998, with a petechial rash associated with hematoma on his trunk, legs, and face. Clinical examination showed hemorrhagic bullae in the mouth and gingival bleeding. No lymphadenopathy or hepatosplenomegaly was observed. His previous medical history included chronic psychosis, which had been treated for 12 years by pipotiazine 12.5 mg every six weeks (last injection April 3, 1998) and trihexyphenidyl 4 mg/d. In February 1998, his physician prescribed glimepiride 1 mg/d, an oral sulfonylurea antidiabetic drug, for hyperglycemia. Platelet counts at the outset of treatment and during the following weeks were not available, but the patient reported no symptoms of bleeding and stopped glimepiride after several weeks of treatment. On April 19, the patient restarted glimepiride treatment and, on April 21, was referred for hemorrhagic syndrome. His platelet count confirmed thrombocytopenia (1 × 1 09/L). A bone marrow aspirate was diluted with peripheral blood, but showed no malignant cells, and there was no serologic evidence of recent viral infection (HIV-1, -2; hepatitis B, C, A; cytomegalovirus; Epstein–Barr virus). The platelet count was too low to assess platelet-associated immunoglobulins, but platelet receptor antibodies were found. All medication was withdrawn; prednisone 1 mg/kg/d and human immunoglobulins 0.4 g/kg/d for 2 d were prescribed. The hemorrhagic syndrome decreased on day 7, but the platelet count was 2 × 1 09/L. After two weeks, the platelet count increased to 23 × 1 09/L and was completely normalized after four weeks of prednisone therapy (281 × 109/L). Prednisone was progressively reduced, and platelet count was normal (346 × 1 09/L) six months after glimepiride was discontinued. D i s c u s s i o n . George et al.4 proposed criteria to evaluate the level of evidence for a causal relationship of drugs to thrombocytopenia. These criteria were: (1) the candidate drug preceded thrombocytopenia, and recovery from thrombocytopenia was complete and sustained after the drug was discontinued; (2) the candidate drug was the only drug used prior to the onset of thrombocytopenia, or other drugs were continued or reintroduced after discontinuation of the candidate drug with a sustained normal platelet count; (3) other etiologies for thrombocytopenia were excluded; and (4) reexposure to the candidate drug resulted in recurrent thrombocytopenia. The level of imputability (definite to unlikely) is definite according to the criteria met. In our observation, the occurrence of thrombocytopenia 48 hours after reintroduction of glimepiride and its resolution after discontinuation of therapy supports the diagnosis of glimepiride-induced thrombocytopenia despite the same criteria of imputability as pipotiazine and trihexyphenidyl according to the Naranjo probability scale.5 The patient had been treated with pipotiazine and trihexyphenidyl for 12 years and had no history of thrombocytopenia or symptoms of bleeding. Pipotiazine and trihexyphenidyl were withdrawn and not reintroduced, but the interval between drug ingestion and the initial occurrence of thrombocytopenia has been reported to be usually less than one day to three years4; therefore, the imputability of these two drugs is unlikely. Other causes of thrombocytopenia were excluded in this patient; even if no reexposure to glimepiride had been attempted, the causal relationship between the drug and thrombocytopenia was probable according to the criteria of George et a l .4 The time to recovery of normal platelet count was four weeks and in agreement with the diagnosis of drug-induced thrombocytopenia. Assay for drug-dependent antiplatelet antibodies was not performed, but no data on the sensitivity and specificity of these assays are available.4 N e vertheless, the occurrence of thrombocytopenia after reintroduction of glimepiride, the severity of thrombocytopenia, and the presence of platelet receptor antibodies argue for an immunoallergic mechanism. In conclusion, some oral antidiabetic drugs such as chlorpropamide and glibenclamide are known to induce thrombocytopenia.1 3 We report the first case of glimepiride-induced thombocytopenia and suggest that platelet counts should be performed when hemorrhagic syndrome is clinically observed during glimepiride treatment.

Malaria antibodies and mefloquine levels among United Nations troops in Angola.

BACKGROUND The United Nations deployed about 8,000 soldiers in a peacekeeping mission in Angola. Malaria is the most common disease there and consequently it was the major risk to the UN troops. Most of them are from malaria free areas. As a result of improper prophylactic measures there were many cases of malaria, including some deaths in 1995. In February-March 1996, an Israeli team was sent to Angola to evaluate the malaria situation among UN soldiers. This paper deals specifically with some aspects of chemoprophylaxis and diagnosis. The efforts were concentrated in one particular area where malaria incidence had been reported as the highest. METHODS Blood samples were collected from nonimmune soldiers who were using mefloquine as a prophylactic drug and were exposed to malaria. The mefloquine and the antimalarial antibody plasma levels were monitored. RESULTS While the local laboratory indicated that about 80% had a malaria episode, the serological results revealed that only 5 soldiers of the 56 (9%) examined had antimalarial antibodies, of which 3 were Angolans. Despite a controlled prophylactic regimen there was considerable variability in mefloquine plasma levels: 46% of the samples were below the required prophylactic level and 26% above it. All patients who were proven positive with malaria by both microscopic and serologic observation had a low level of mefloquine. CONCLUSIONS In field conditions, a kit which identifies plasmodial antigens, is preferable, to a microscopic diagnostic method. Controlled mefloquine prophylaxis may not prevent malaria, especially when blood levels are low. The reason for the low mefloquine blood levels is not clear and needs further evaluation.

The pharmacokinetics of morphine and lidocaine in nine severe trauma patients

STUDY OBJECTIVE To study the pharmacokinetic parameters of morphine and lidocaine after a single intravenous (i.v.) bolus in severe trauma patients. DESIGN Clinical case study. SETTING Department of Anesthesiology and Intensive Care of a university hospital. PATIENTS Nine patients, ages 24 to 91 years (mean 54.4 yrs), admitted to the hospital with severe trauma (Injury Severity Score > 20) were included in the study. INTERVENTIONS After initial evaluation and stabilization, a single i.v. dose of morphine 0.025 mg/kg and lidocaine 1.5 mg/kg was given separately, and blood samples were drawn for each drug serum concentration. MEASUREMENTS AND MAIN RESULTS Morphine pharmacokinetics was studied in eight patients, lidocaine pharmacokinetics in seven patients, and both drugs were studied in six patients. Morphine clearance 2.5 to 10 ml/kg/min (6 +/- 2.6, mean +/- SD) and volume of distribution 0.28 to 3.30 L/kg (1.4 +/- 1.0) were found to be lower than values described previously for healthy volunteers (33.5 +/- 9 ml/kg/min and 5.16 +/- 1.40 L/kg, respectively), and are similar to those described in trauma patients (5 +/- 2.9 ml/kg/min and 0.9 +/- 0.2 L/kg, respectively). In contrast, lidocaine clearance 4.5 to 9.4 ml/kg/min (6.7 +/- 1.7) and volume of distribution 0.39 to 1.20 L/kg (0.72 +/- 0.28) were similar to the value described in healthy volunteers (10 ml/kg/min and 1.32 L/kg, respectively). CONCLUSION Changes in pharmacokinetics of drugs eliminated by the liver may occur in patients with severe trauma. The preserved lidocaine clearance indicates an almost normal hepatic blood flow and suggests that other mechanisms may be involved in the lower morphine clearance. The findings may have applications for the treatment of severe trauma patients and suggest that drug monitoring might be needed in some instances so as to avoid toxicity.

Evaluation of the decarbamylation process of cholinesterase during assay of enzyme activity

The activity of carbamylated cholinesterase increases continuously during assay, suggesting that progressive decarbamylation takes place. The following effects of assay conditions on the observed decarbamylation were studied: the effect of the sulfhydryl group of nitrobenzoate produced in the course of Ellman assay, the effect of substrate and the effect of sample dilution during assay. This study indicates that sample dilution is the main trigger to the decarbamylation observed during assay of cholinesterase activity. The process was described as a first-order reaction during which the inhibited enzyme gives place to the active form. Kinetic constants for decarbamylation of human pseudocholinesterase (EC 3.1.1.8) at 30 degrees C were approximately 0.005 min-1 for dimethylcarbamates and 0.010 min-1 for monomethylcarbamates, when 1 mmol/l propionylthiocholine was used as substrate.

Association between prenatal exposure to metals and neonatal morbidity.

An association between prenatal exposure to (semi-)metals and of neonatal morbidity was assessed by introducing an oxidative stress as a possible intermediate step. An oxidative stress was measured by cell proliferation (CP) ratio in umbilical cord blood cells. Urine samples of 18 out of 58 enrolled women (31%) were positive for (semi-)metals; 25.9% of women were positive for aluminum (Al). The CP ratio was higher (1) in subjects with Al, (2) in mothers to newborns diagnosed as small-for-gestational age (p value = .052), (3) neonates that weighed less (p value = .079), and (4) in women who experienced repeated abortions (p value = .049). Our findings suggest the possibility of metal-induced oxidative stress.

Exposure to metals and congenital anomalies: A biomonitoring study of pregnant Bedouin-Arab women

BACKGROUND The Bedouin-Arab population in Israel comprises a low socio-economic society in transition. Smoking among males and consanguineous marriages are frequent. A previous study showed elevated rates of major malformations within groups from this population residing near an industrial park, where high ambient values of arsenic (As) and nickel (Ni) were detected, compared to groups living in remote localities. OBJECTIVES We estimated the extent of exposure to metals in pregnant Bedouin-Arab women in relation to congenital malformations. METHODS We collected maternal urine samples from 140 Bedouin women who gave birth in a local hospital. Patient medical history, type of marriage (consanguineous or non-consanguineous), and parental exposure history were collected by interview and medical records. RESULTS Aluminum (Al) was detected in 37 women (26.4%), cadmium (Cd) in 2 (1.4%), As in 10 (7.1%), and Ni in 1 woman (0.7%). The detected rate of Cd exposure was low, though more than 92% of the fathers reported smoking. Concentrations of Al were higher for women residing within 10 km of the local industrial park (Prevalence Ratio (PR)=1.12, p-value=0.012) or who reported using a wood burning stove (PR=1.37, p-value=0.011) and cooking over an open fire (PR=1.16, p-value=0.076). Exposure to Al was adversely associated with minor anomalies (OR=3.8, p-value=0.046) after adjusting for history of abortions (OR=6.1, p-value=0.007). Fetuses prenatally exposed to As were born prematurely (p-value=0.001) and at lower weights (pv=0.023). CONCLUSIONS The study population of pregnant women is exposed to high levels of metals mainly of household origin. Our findings may be generalized to similar populations in developing countries.

Functional effects of synthetic cannabinoids versus Δ9-THC in mice on body temperature, nociceptive threshold, anxiety, cognition, locomotor/exploratory parameters and depression: Synthetic cannabinoids mice

Synthetic cannabinoids are psychoactive substances designed to mimic the euphorigenic effects of the natural cannabis. Novel unregulated compounds appear once older compounds become illegal. It has been previously reported that synthetic cannabinoids are different than Δ9‐tetrahydrocannabinol (Δ9‐THC) as they have chemical structures unrelated to Δ9‐THC, different metabolism and, often, greater toxicity. This study aimed to investigate the effects of three novel synthetic cannabinoids and pure Δ9‐THC on body temperature, nociceptive threshold, anxiety, memory function, locomotor and exploratory parameters, and depression. We performed a battery of behavioural and motor tests starting 50 minutes post i.p. injection of each drug to adult ICR mice. The synthetic cannabinoids that were used are AB‐FUBINACA, AB‐CHMINACA and PB‐22. All synthetic cannabinoids and Δ9‐THC caused hypothermia, but only Δ9‐THC induced a clear antinociceptive effect. All synthetic cannabinoids and Δ9‐THC caused decreased anxiety levels, spatial memory deficits and decreased exploratory behaviour as measured in the elevated plus maze, Y‐maze and staircase paradigm, respectively. However, all synthetic cannabinoids but not Δ9‐THC demonstrated decreased locomotor activity in the staircase test. Moreover, only AB‐FUBINACA and Δ9‐THC affected the gait balance and grip strength of the mice as was assessed by the latency time to fall from a rod. In the forced swimming test, PB‐22 caused elevated depression‐like behaviour while AB‐FUBINACA induced a reversed effect. These results suggest varied effects among different synthetic cannabinoids and Δ9‐THC. Further studies are needed to characterize the overall effects and differences between these synthetic cannabinoids and Δ9‐THC.