Faculty Bibliography

Methylene blue is used primarily in the treatment of patients with methemoglobinemia. Most recently, methylene blue has been used as a treatment for refractory distributive shock from a variety of causes such as sepsis and anaphylaxis. Many studies suggest that the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway plays a significant role in the pathophysiology of distributive shock. There are some experimental and clinical experiences with the use of methylene blue as a selective inhibitor of the NO-cGMP pathway. Methylene blue may play a role in the treatment of distributive shock when standard treatment fails.

BACKGROUND: Flecainide is a class IC antidysrhythmic primarily indicated for ventricular dysrhythmias and supraventricular tachycardia (SVT). Class IC antidysrhythmic overdose has a reported mortality of 22%, and death results from dysrhythmias and cardiovascular collapse. We report a near-fatal flecainide overdose in an 18-day-old treated successfully with sodium bicarbonate. CASE REPORT: An 18-day-old, 2 weeks premature, 4-kg boy developed persistently high heart rates (220-240 beats/min) and electrocardiographic changes consistent with SVT. There was minimal response to vagal maneuvers, adenosine, and esmolol, and a transthoracic echocardiogram showed no underlying structural abnormality. The patient was then started on flecainide 4 mg orally every 8 h (Q8h). After the fourth dose he developed lethargy, cold clammy skin, and a heart rate of 40 beats/min with no palpable pulse. The patient was given 0.1 mg of atropine intravenously, with an increase of the heart rate to 160 beats/min. The child's cardiac monitor revealed a wide-complex tachycardia with left bundle branch morphology, with associated pallor and poor capillary refill. Sodium bicarbonate was administered intravenously due to suspected flecainide toxicity. Approximately 5 min after intravenous administration of 10 mEq of 8.4% sodium bicarbonate twice, his rhythm converted to a narrow-complex tachycardia. A serum flecainide concentration was 1360 mug/L (therapeutic, 200-1000 mug/L) drawn 1 h before the cardiac arrest. It was later discovered that a twofold dosing error occurred: the patient received 8 mg Q8h instead of 4 mg Q8h for four doses. CONCLUSION: Flecainide toxicity in children is rare, especially in neonates. It is important for clinicians to be able to identify and treat this uncommon poisoning.

BACKGROUND: Cardiovascular drug poisoning remains a leading cause of fatality. Within this class, calcium channel blockers (CCBs) account for the majority of deaths. CCBs are typically categorized as dihydropyridines (i.e. amlodipine or nifedipine) versus the non-dihydropyridine (i.e. verapamil and diltiazem) which are the most potent and once considered the CCB type responsible for all CCB-related deaths. Most recently, dihydropyridine deaths have increased. While there are established models of nondihydropyridine poisoning there currently are no established experimental models of dihydropyridine poisoning. METHODS: Electrocardiogram electrodes and intravenous lines were placed in anesthetized Spraque-Dawley rats. Various doses of amlodipine were administrated as a constant infusion to mimic continued gastrointestinal absorption. Intravenous amlodipine dosing was determined by the Dixon "up-and-down" method. Animals were observed for a total of two hours and death or survival was recorded. RESULTS: Various solvents were used such as tween and ethanol. Amlodipine was successfully dissolved in 20% DMSO. The maximum likelihood estimate for LD50 was 8.65 mg/kg (SE, +/- 2.67 mg/kg). CONCLUSIONS: A reliable experimental model of dihydropyridine poisoning using intravenous amlodipine is presented which will allow future studies concerning pathophysiology of shock from dihydropyridine poisoning and treatment.

INTRODUCTION: In the treatment of acetaminophen toxicity, clinicians believe that N-acetylcysteine (NAC) artificially elevates prothrombin time (PT). However, the effect of NAC on human blood coagulation remains unverified. In a previous study, we show that NAC had a dose-dependent effect on PT. To our knowledge, there are no studies that specifically examine the mechanism by which NAC affects PT. This study evaluates the effect from a therapeutic NAC dose on the activity of coagulation factors II, VII, IX, and X in human plasma. METHOD: We obtained blood samples from ten volunteer subjects. After centrifugation of each volunteer's blood sample, the plasma was pipetted and divided into two 1-mL aliquots. We used the first-1 mL sample as a control. The second 1-mL plasma sample had 5 muL of 20 % NAC, added to make a final concentration of 1,000 mg of NAC per L of plasma. This concentration of NAC approximates the plasma levels achieved after a 150-mg/kg dose. We incubated the two samples for each subject (control and 1,000 mg/L) at 37 degrees C for 1 h and measured the activity of coagulation factors II, VII, IX, and X. We compared factor activity using the paired student t test. RESULTS: Participants included ten healthy subjects; six males, four females, median age 31 years. Mean values of the control samples for factors II, VII, IX, and X were 134 (CI 119-149), 126 (CI 90-163), 137 (CI 117-157), and 170 (CI 144-196) %, respectively. Mean values of the NAC-containing samples for factors II, VII, IX, and X were 90 (CI 79-100), 66 (CI 51-80), 74 (CI 63-85), and 81 (CI 71-90) %, respectively. All samples containing NAC had significantly lower coagulation factor activity level than their controls with a p < 0.001. DISCUSSION: In a previous study, we were able to demonstrate that NAC had a dose-dependent effect on PT. In this study, we compared activity of factors II, VII, IX, and X at baseline and for samples that received NAC. All factor activity had a significant decrease with the addition of NAC. This fall in factor activity is not explained by the dilution of adding NAC to the test samples. CONCLUSION: We are able to demonstrate a significant decrease in the activity of coagulation factors II, VII, IX, and X with the addition of NAC. This may be the mechanism by which PT increased in our previous study.