Subconstrictor doses of neuropeptide Y potentiate alpha 1-adrenergic venoconstriction in vivo

The 36-amino acid human neuropeptide Y is a vasoactive compound released after stimulation of the sympathetic nervous system. In addition to its direct and long-lasting vasopressor effects, it may potentiate the constrictor action of catecholamines and other vasoconstrictors at doses that do not per se exert vascular effects. Using the hand vein compliance technique, we have previously shown that neuropeptide Y also constricts superficial hand veins and that its effects may last for several hours. In this study, we investigated the local effect of neuropeptide Y on alpha 1-adrenergic venoconstriction in nine healthy volunteers at dose rates that did not affect venous compliance. On separate days, cumulative dose-response curves to phenylephrine alone and with coadministration of 1 or 30 pmol neuropeptide Y per minute were constructed, and the responses were fitted to a four-parameter logistic equation. Neuropeptide Y dose dependently shifted the phenylephrine curves toward lower dose rates without affecting maximal effects. ED50 values for phenylephrine alone and with 1 or 30 pmol/min neuropeptide Y were 4.0, 4.9 (P = NS versus control), and 1.2 (P < .005) nmol/min, respectively. Comparison with neuropeptide Y dose-response curves revealed that the interaction was synergistic. These are the first data in humans to show that small dose rates of neuropeptide Y may potentiate alpha-adrenergic effects in vivo. Because this interaction occurs at estimated local concentrations nearly achieved in humans, these studies suggest that neuropeptide Y might modulate the filling of this capacitance system in vivo.

N-acetyltransferase 2 polymorphism in patients infected with human immunodeficiency virus

OBJECTIVES

To evaluate the prevalence of slow acetylation of hepatic N-acetyltransferase 2 (NAT2) in patients with different stages of human immunodeficiency virus (HIV) infection, to assess the relationship between acetylation capacity and the degree of immunosuppression, and to study the concordance between NAT2 phenotype and genotype.

METHODS

This prospective study in a consecutive sample of HIV-infected patients was performed in the outpatient department of a university hospital that provides primary and tertiary care. The NAT2 genotype was assessed by polymerase chain reaction and restriction fragment length polymorphism, the NAT2 phenotype was determined by caffeine test (urinary metabolic ratio of the caffeine metabolites 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine).

RESULTS

Fifty patients with Centers for Disease Control HIV infection stages A (10 patients), B (20 patients), and C (20 patients) were included in the study after each gave informed consent. According to genotyping and phenotyping, 32 (64%) patients were slow acetylators, with a concordance of the two methods of 96%. The overall distribution was similar to distributions reported in other white populations. The slow acetylator phenotype was found in seven, 16, and nine patients with stage A, B, and C, respectively. Eight of the 10 patients with previous adverse reactions to sulfonamides had slow acetylator phenotypes. Acetylation capacity was independent of CD4 cell counts.

CONCLUSIONS

This study revealed an excellent agreement between genotypes and phenotypes of NAT2 in patients with HIV infection. There was no increase in prevalence of slow acetylation in patients with advanced stages of the disease. This apparent discrepancy to an earlier study may be the result of differences in co-medication of the patients studied and may point to the relevance of drug interactions in the treatment of patients with HIV infection.

Effect of methionine loading on 5-methyltetrahydrofolate, S-adenosylmethionine and S-adenosylhomocysteine in plasma of healthy humans

1. Elevated plasma homocysteine concentration, either in the fasting state or after methionine loading, is an independent risk factor for vascular disease in man. Methionine loading has been used to investigate impaired methionine metabolism, especially of the trans-sulphuration pathway, but most studies have focused on changes in homocysteine. 2. We investigated the effect of methionine excess on total plasma homocysteine, 5-methyltetrahydrofolate (which is the active form of folate in the remethylation of homocysteine to methionine), S-adenosyl-methionine (the first metabolite of methionine) and S-adenosylmethionine) (the demethylated product of S-adenosylmethionine) over 24h in 12 healthy subjects. 3. As well as the expected increase in homocysteine (from 8.0 +/- 1.3 to 32.6 +/- 10.3 mumol/l, mean +/- SD, P < 0.001), S-adenosylmethionine showed a significant transient increase (from 37.9 +/- 25.0 to 240.3 +/- 109.2 nmol/l, P < 0.001), which correlated well with homocysteine (r2 = 0.92, P < 0.001). 5-Methyltetrahydrofolate values decreased significantly (from 23.2 +/- 7.2 to 13.1 +/- 2.9 nmol/l, P < 0.01), and gradually returned to baseline levels after 24h. No significant change over the time of measurement was found for S-adenosylhomocysteine. 4. The sequence of metabolic changes observed in this study strongly suggests that a change in either homocysteine or S-adenosylmethionine may cause a reduction in 5-methyltetrahydrofolate. This must be considered in evaluating the relationship between folate and homocysteine in vascular disease. The metabolic relationships illustrated in this study should be evaluated in the search for pathogenetic mechanisms of mild hyperhomocysteinaemia and vascular disease.

Low whole-blood S-adenosylmethionine and correlation between 5-methyltetrahydrofolate and homocysteine in coronary artery disease

Mild elevation of plasma homocysteine is an independent risk factor for vascular disease. We studied the role of 5-methyltetrahydrofolate (5-MTHF), the folate form directly involved in homocysteine metabolism, in contrast to previous studies, which used total folate measurements, in 70 coronary artery disease (CAD) patients and control subjects. We also measured S-adenosylmethionine (SAM), which controls the activity of critical enzymes of homocysteine metabolism. Fasting plasma total homocysteine was elevated (> 12.4 mumol/L for women, > 13.3 mumol/L for men) in 17% of patients, in accordance with earlier studies. These patients showed lower 5-MTHF (12.4 +/- 1.0 mumol/L, mean +/- SD) than control subjects (24.2 +/- 15.0, P < .001), and there was a clear correlation (multiple linear regression analysis: P = .002) of this relevant form of folate with homocysteine. However, 37% of the normohomocysteinemic patients also revealed similarly low 5-MTHF levels, suggesting that a decrease of 5-MTHF does not necessarily cause hyperhomocysteinemia. SAM was significantly decreased in patients (1.4 +/- 0.4 mumol/L) compared with control subjects (1.8 +/- 0.3, P < .001) but was not correlated to homocysteine or 5-MTHF. The correlation between homocysteine and 5-MTHF that was found in CAD patients but not in control subjects confirms the direct relationship between these compounds in vivo. The new finding of low SAM in patients demands further studies, since it might indicate that low levels pose risk and that SAM might be a protective factor against the development of CAD.

Neuropeptide Y in human hand veins: pharmacologic characterization and interaction with cyclic guanosine monophosphate-dependent venodilators in vivo

The dorsal hand vein compliance technique was used to study direct vascular effects of human neuropeptide Y in vivo. Human neuropeptide Y is an endogenous vasoconstrictor peptide that is costored with norepinephrine in sympathetic nerve endings and coreleased with the catecholamine under various physiologic and pathologic conditions. Compared with the alpha 1-adrenergic agonist phenylephrine (geometric mean dose-rate that produces the half-maximal response [ED50]: 1.05 nmol/min; maximum venoconstriction [Emax] +/- SEM, expressed as a percentage of baseline compliance: 91% +/- 3%), human neuropeptide Y was nine times more potent (geometric mean ED50: 0.122 nmol/min; p < 0.001) but markedly less efficacious (Emax: 58% +/- 4%; n = 12; p < 0.001). Venoconstrictor effects of human neuropeptide Y lasted several hours and were unchanged by simultaneous administration of alpha-adrenergic antagonists but were readily reversed by nitroglycerin or bradykinin. The high responsiveness of subcutaneous veins to human neuropeptide Y indicates that human neuropeptide Y may regulate venous compliance and filling of the venous subcutaneous capacitance bed in vivo.

Indirect evidence for stimulation of nitric oxide release by tumour necrosis factor-alpha in human veins in vivo

OBJECTIVES

The detrimental haemodynamic changes observed in septicaemia are generalised vasodilation, arterial hypotension, and hyporesponsiveness to vasopressor compound, all of which could be explained by the release of an endogenous vasodilator. Experimental and clinical evidence suggests that tumour necrosis factor-alpha (TNF) induces the expression of vascular nitric oxide (NO) synthase within hours and that NO released from smooth muscle cells could be involved in the pathogenesis of septic shock. The aim of this study was to investigate the role of NO in the vascular effects of TNF.

METHODS

Using the dorsal hand vein compliance technique, the effect of the NO synthase inhibitor L-NG-monomethyl-arginine (L-NMMA) on alpha 1-adrenergic responsiveness (phenylephrine 1.25-8000 ng/min) was studied after prolonged local venous infusion of TNF (8.7 micrograms in 5 h) in 9 volunteers and in 6 volunteers without previous cytokine exposure.

RESULTS

Mean (+/- s.e.) maximum phenylephrine constriction (Emax) was 73 +/- 6% and log dose-rates exerting 50% of Emax (log ED50) were 3.2 +/- 0.09 (geometric mean: 1535 ng/min). Local co-administration of L-NMMA at a dose sufficiently high to block NO formation (3.4 mumol/min) increased venous sensitivity to phenylephrine threefold (log ED50 2.8 +/- 0.1, P < 0.015; geometric mean: 574 ng/min) whereas Emax was similar (73 +/- 5%). In the controls the phenylephrine dose-response relationship remained unaffected by simultaneous administration of L-NMMA.

CONCLUSIONS

As no basal release of NO occurs in hand veins without previous exposure to TNF these results provide direct evidence for induction of NO formation in the human vasculature and consecutive resistance to alpha-adrenergic venoconstriction. NO might, therefore, be a key mediator of haemodynamic impairment in humans under conditions with known elevations of circulating TNF, such as a septic shock.

Role of basal and stimulated release of nitric oxide in the regulation of radial artery caliber in humans

Although it is well established that nitric oxide contributes to the regulation of resistance arterial tone in humans, its role at the level of large arteries is less clear. Therefore, we assessed in healthy volunteers the effect of local administration of the inhibitor of nitric oxide synthesis NG-monomethyl-L-arginine (L-NMMA) on basal radial artery diameter (transcutaneous A-mode echotracking) and radial blood flow (Doppler) as well as on the radial response to acetylcholine and the nitric oxide donor sodium nitroprusside. A catheter was inserted into the brachial artery for measurement of arterial pressure and infusion of L-NMMA (2, 4 and 8 mumol/min for 5 minutes, n = 11), acetylcholine (3, 30, 300 and 900 nmol/min for 3 minutes, n = 8), and nitroprusside (2.5, 5, 10, and 20 nmol/min for 3 minutes, n = 6). None of the treatments affected arterial blood pressure or heart rate. L-NMMA dose-dependently decreased radial blood flow (from 31 +/- 6 to 17 +/- 3 10(-3) L/min after 8 mumol/min, P < .01) but did not affect radial artery diameter (from 2.93 +/- 0.11 to 2.90 +/- 0.14 mm). Acetylcholine dose-dependently increased radial blood flow (154 +/- 43% after 900 nmol/min) and radial artery diameter (16 +/- 4%), and both effects were markedly reduced after L-NMMA (increase in radial blood flow and radial artery diameter: 22 +/- 20% and 3 +/- 2%, respectively; both P < .01 versus controls). Nitroprusside also dose-dependently increased radial artery diameter (14 +/- 4% after 20 nmol/min) but only moderately affected radial blood flow (47 +/- 21%).(ABSTRACT TRUNCATED AT 250 WORDS)

[Role of nitric oxide in the regulation of the mechanical properties of peripheral muscular arteries in man]

Although several experiments have demonstrated the existence of a basal NO-dependent vasodilatory tone at the arteriolar level, the contribution of NO to the mechanical properties of large arteries has not been investigated in humans. To evaluate the effect of NO-synthase inhibition on these mechanical properties, radial artery internal diameter (d, mm) and wall thickness (h, mm) were measured continuously in 11 healthy volunteers (age: 24 +/- 1 years), using an A-mode echo-tracking system coupled to a Doppler device for the measurement of radial blood flow (RBF, ml/min). A catheter was inserted in the brachial artery for measurement of arterial pressure (AP, mmHg), and infusion of the inhibitor of NO synthesis NG-monomethyl L-arginine (L-NMMA: 4 mumol/min for 5 min, infusion rate 0.8 ml/min). Arterial compliance C, 10(-3) mm2/mmHg), distensibility (D, 10(-3)/mmHg), mid-wall stress (sigma, 10(5) dynes/mm2) and incremental modulus (Ei, 10(7) dynes/mm2) were calculated before and after L-NMMA. After L-NMMA, RBF decreased from 31 +/- 6 to 23 +/- 4 (p < 0.05), radial vascular resistance increased from 2.70 +/- 0.35 to 3.77 +/- 0.55 (p < 0.05), without changes in AP or heart rate. Table shows mechanical parameters, assessed at fixed AP (80 mmHg) (*: p < 0.05 vs baseline): [table: see text] Thus, the L-NMMA-induced decrease in radial arterial wall stiffness (Ei) without changes in arterial diameter or stress demonstrates that NO-synthase inhibition induces an isometric relaxation of vascular muscle cells, which explains the increase of arterial compliance at constant mid-wall stress. These results demonstrate that NO contributes to the regulation of peripheral muscular arterial mechanics in humans. At the level of large arteries, the isometric relaxation observed after NO-synthase inhibition is probably the consequence of compensatory vasodilator mechanisms.

Prolonged sedation due to accumulation of conjugated metabolites of midazolam

Midazolam is a short-acting benzodiazepine routinely used in intensive-care medicine. Conjugates of its main metabolite, alpha-hydroxymidazolam, have been shown to accumulate in renal failure but have not previously been related to the prolonged sedative effects commonly observed in critically ill patients. We report five patients with severe renal failure who had prolonged sedation after administration of midazolam. In all five patients, the comatose state was immediately reversed by the benzodiazepine-receptor antagonist flumazenil. Serum concentration monitoring showed high concentrations of conjugated alpha-hydroxymidazolam when concentrations of the unconjugated metabolite and the parent drug were below the therapeutic range. In-vitro binding studies showed that the affinity of binding to the cerebral benzodiazepine receptor of glucuronidated alpha-hydroxymidazolam was only about ten times weaker (affinity constant 16 nmol/L) than that of midazolam (1.4 nmol/L) or unconjugated alpha-hydroxymidazolam (2.2 nmol/L). Conjugated metabolites of midazolam have substantial pharmacological activity. Physicians should be aware that these metabolites can accumulate in patients with renal failure.

Nitric oxide is responsible for flow-dependent dilatation of human peripheral conduit arteries in vivo

BACKGROUND

Experimental evidence suggests that flow-dependent dilatation of conduit arteries is mediated by nitric oxide (NO) and/or prostacyclin. The present study was designed to assess whether NO or prostacyclin also contributes to flow-dependent dilatation of conduit arteries in humans.

METHODS AND RESULTS

Radial artery internal diameter (ID) was measured continuously in 16 healthy volunteers (age, 24 +/- 1 years) with a transcutaneous A-mode echo-tracking system coupled to a Doppler device for the measurement of radial blood flow. In 8 subjects, a catheter was inserted into the brachial artery for measurement of arterial pressure and infusion of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 8 mumol/min for 7 minutes; infusion rate, 0.8 mL/min). Flow-dependent dilatation was evaluated before and after L-NMMA or aspirin as the response of the radial artery to an acute increase in flow (reactive hyperemia after a 3-minute cuff wrist occlusion). Under control conditions, release of the occlusion induced a marked increase in radial blood flow (from 24 +/- 3 to 73 +/- 11 mL/min; P < .01) followed by a delayed increase in radial diameter (flow-mediated dilatation; from 2.67 +/- 0.10 to 2.77 +/- 0.12 mm; P < .01) without any change in heart rate or arterial pressure. L-NMMA decreased basal forearm blood flow (from 24 +/- 3 to 13 +/- 3 mL/min; P < .05) without affecting basal radial artery diameter, heart rate, or arterial pressure, whereas aspirin (1 g PO) was without any hemodynamic effect. In the presence of L-NMMA, the peak flow response during hyperemia was not affected (76 +/- 12 mL/min), but the duration of the hyperemic response was markedly reduced, and the flow-dependent dilatation of the radial artery was abolished and converted to a vasoconstriction (from 2.62 +/- 0.11 to 2.55 +/- 0.11 mm; P < .01). In contrast, aspirin did not affect the hyperemic response nor the flow-dependent dilatation of the radial artery.

CONCLUSIONS

The present investigation demonstrates that NO, but not prostacyclin, is essential for flow-mediated dilatation of large human arteries. Hence, this response can be used as a test for the L-arginine/NO pathway in clinical studies.

[Role of nitric oxide in flow-dependent vasodilation of human peripheral arteries in vivo]

Experiments performed in isolated arteries or in animals suggested that flow-dependent dilatation of conduit arteries is mediated through the release of endothelium-derived nitric oxide (NO). The present study was designed to assess whether NO also contributes to flow-dependent dilatation of conduit arteries in humans. Radial artery internal diameter was measured in 8 healthy volunteers (age 22 +/- 1 years), using a transcutaneous A-mode echo-tracking system, coupled to a Doppler device for the measurement of radial blood flow. A catheter was inserted in the brachial artery for measurement of arterial pressure and infusion of the L-arginine analogue NG-monomethyl L-arginine (L-NMMA (8 mumol/min for 7 min, infusion rate 0.8 ml/min). Flow-dependent dilatation was evaluated before and after L-NMMA as the response of the radial artery to an acute increase in flow (reactive hyperemia after a 3 min distal cuff occlusion). Release of the occlusion induced a significant increase in radial blood flow (from 27 +/- 4 to 82 +/- 13 ml/min; p < 0.01) followed by a delayed increase in radial diameter (flow-mediated dilatation; from 2.77 +/- 0.13 to 2.85 +/- 0.13 min; p < 0.01), without any change in heart rate or arterial pressure. L-NMMA induced a significant decrease in basal forearm blood flow (from 27 +/- 4 to 14 +/- 2 ml/min; p < 0.05), without affecting basal radial artery diameter, heart rate or arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian carbamazepine toxicity

Owing to marked fluctuations in plasma concentrations, circadian CNS toxicity (maximum in the early afternoon) occurred in a 69-year-old female patient being treated with an instant-release formulation of carbamazepine (CBZ). The neurologic syndrome was reversible after administration of the same daily dose as sustained-release formulation. This case illustrates the importance of correct timing of blood sampling to detect drug-induced toxicity and of use of sustained-release formulations in antiepileptic therapy with CBZ.

Responsiveness to bradykinin in veins of hypercholesterolemic humans

BACKGROUND

Hypercholesterolemia impairs endothelium-dependent dilation in arteries. We tested the hypothesis that hypercholesterolemia impairs endothelium-dependent vasodilation by an interaction between elevated plasma lipoproteins and a presumably normal endothelium using human veins in vivo; veins do not generally develop atherosclerosis and are appropriate for testing functional alterations.

METHODS AND RESULTS

Full dose-response curves were constructed in 13 hypercholesterolemic and 12 normocholesterolemic subjects by infusing bradykinin (0.25 to 508 ng/min) into hand veins preconstricted with the alpha-adrenergic agonist phenylephrine. The maximal relaxation induced by bradykinin was 80 +/- 38% in the controls and 103 +/- 40% in subjects with hypercholesterolemia (P = .08). Responsiveness to bradykinin was also determined after infusion of indomethacin (5.4 micrograms/min), a cyclooxygenase inhibitor, to block the contribution of prostaglandins; maximal responsiveness was greater in hypercholesterolemic subjects (112 +/- 41%) than in controls (81 +/- 31%) (P = .03). Hypercholesterolemic subjects were more sensitive to bradykinin, with an ED50 of 4.2 ng/min versus 10.9 ng/min in controls (P = .05); a similarly increased sensitivity was found in the presence of indomethacin. The response to a maximally effective dose of nitroglycerin was greater in hypercholesterolemic subjects (142 +/- 31%) versus 106 +/- 28% in controls (P = .007). In five hypercholesterolemic subjects, treated with lovastatin to normalize serum cholesterol concentrations, maximal responsiveness to bradykinin decreased from 103 +/- 52% to 80 +/- 28%.

CONCLUSIONS

These results demonstrate that hypercholesterolemia in humans does not impair endothelium-derived relaxing factor-mediated venodilation.

Evaluation of conventional chest tube therapy for iatrogenic pneumothorax

STUDY OBJECTIVE

To assess conventional, large chest tube therapy in iatrogenic pneumothorax and to determine the optimal moment when to use more invasive procedures.

DESIGN

Retrospective chart review.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Forty-seven patients with needle-induced iatrogenic pneumothorax. Twenty-four patients had an underlying pleural or pulmonary disorder.

INTERVENTIONS

After insertion of a 20- to 24-French plastic chest tube connected to an underwater seal, suction was maintained until gas egress stopped or up to 10 days in patients with a persisting gas leak.

RESULTS

In 96 percent, a definite occlusion of the pneumothorax was achieved. In all patients without an underlying lung disorder, gas egress stopped definitely after 72 h. In the presence of an underlying lung disorder, 92 percent of the pneumothoraces were healed after 10 days of continuous suction therapy. At 72 h, only 71 percent of the latter group were healed (p < 0.05 vs patients without lung disease). No major complication of chest tube therapy occurred.

CONCLUSION

Conventional chest tube therapy is a safe and effective treatment for iatrogenic pneumothorax. In patients with an underlying lung disease, gas egress may last for up to 10 days. In these patients, the earlier use of a more invasive approach may be justified if the air leak persists.

[Drug-induced Stevens-Johnson syndrome in a patient with AIDS]

The Stevens-Johnson syndrome is a severe potentially life-threatening form of the erythema multiforme, affecting both skin and mucous membranes. We present a case of a 49-year-old male patient with AIDS who developed a Stevens-Johnson syndrome while being treated with pyrimethamine, sulfadiazine and phenytoin for cerebral toxoplasmosis. Further diagnostic evaluation of this dangerous cutaneous affection may prove difficult for several reasons. In particular, in patients with AIDS who are more susceptible for adverse drug reactions and who are simultaneously receiving a variety of drugs with a considerable potential of cutaneous side effects, therapy cannot be withhold for lack of therapeutic alternatives. Moreover, the low lymphocyte count in this case may have made reliable testing with lymphocyte transformation studies impossible. The evaluation and the differential diagnosis of the drug-induced Stevens-Johnson syndrome are discussed. Especially long- and moderately long-acting sulfonamides belong to the most important agents that can cause a drug-induced Stevens-Johnson syndrome. The pathogenesis and the risk factors for cutaneous hypersensitivity reactions in HIV-infected patients are only poorly understood. These kind of reactions, however, seem to occur more often in patients with a more advanced immunodeficiency.

Glutathione S-transferase mu polymorphism does not explain variation in nitroglycerin responsiveness

OBJECTIVE

To determine whether the considerable interindividual variability in nitroglycerin-induced venodilation in humans is related to the polymorphic expression of the mu class of glutathione S-transferase (GST mu). Recently vascular glutathione S-transferase (EC 2.5.1.18) of the mu-class (GST mu), a polymorphic group of enzymes present in only about 60% of the population, have been identified and shown in vitro to possess high metabolic activity toward nitroglycerin. Their clinical relevance is unknown.

DESIGN

Dose-response relationships to nitroglycerin were constructed in vivo measuring changes in compliance of dorsal hand veins in 26 healthy volunteers during local infusion of small amounts of nitroglycerin. Polymerase chain reaction was applied to detect the deoxyribonucleic acid sequence that codes GST mu in whole blood samples.

RESULTS

The GST mu isozyme was present in 15 subjects (58%) and deficient in 11 subjects. Values for mean maximum venodilation (Emax) and dose rates producing 50% of Emax (ED50) were not significantly different between the groups with or without GST mu. The respective values were 98% and 103% dilation for Emax and 9 and 16 ng/min for ED50. There was no gender difference in the venodilatory response to nitroglycerin.

CONCLUSIONS

Subjects lacking GST mu can clearly respond normally to nitroglycerin, and the large interindividual variability in nitroglycerin potency is not related to the expression of this polymorphic enzyme. Intersubject variability is therefore more likely to be the result of differences in the presence or activity of other vascular enzymes or in steps further distal in the venodilatory cascade.

[Torsade de pointes during anti-arrhythmia treatment with amiodarone]

Torsade de pointes, a polymorphous ventricular tachycardia, is a well-known but rarely occurring cardiac adverse drug reaction under amiodarone, a class-III antiarrhythmic agent. We report the case of a 60-year-old male patient who developed a life-threatening torsade after three weeks of amiodarone therapy. Considering some potential risk factors, amiodarone is an effective and safe antiarrhythmic agent for ventricular and supraventricular tachycardia. In most patients, Amiodarone can be used safely even in those who had developed a torsade de pointes with other antiarrhythmic agents.

Evidence for activation of the sympathetic nervous system by recombinant human interleukin-1 beta in humans

Administration of interleukin-1 beta (IL-1 beta) to humans initiates a cascade of metabolic, hematologic, and cardiovascular events. To investigate the role of the sympathetic nervous system in the early cardiovascular response to IL-1 beta in humans, we recorded the heart rate, blood pressure, and changes in hand vein compliance in five patients with malignant melanoma treated with a 30-min infusion of 10,000-20,000 U/kg of human recombinant IL-1 beta. All patients developed fever, chills, and marked hemodynamic changes. During or shortly after the infusion, a dramatic decrease in hand vein compliance occurred (vasoconstriction). At the time of maximum venoconstriction (35 min after the start of the IL-1 beta infusion), the mean heart rate and systolic blood pressure were significantly increased by 30 mm Hg and 31 beats/min, respectively. Venoconstriction always preceded the onset of chills by several minutes (mean of 7 min), was closely correlated with the heart rate, and could be reversed by local administration of the alpha-antagonist phentolamine, indicating involvement of catecholamines. Our study shows that cardiovascular responses that occur early after IL-1 beta administration in humans are most likely the result of adrenergic stimulation possibly through its effect on the central nervous system.

Acyclovir-induced neurotoxicity: concentration-side effect relationship in acyclovir overdose

PURPOSE

To investigate the concentration-side effect relationship in a patient with severe acyclovir-induced neurotoxicity and to summarize the information available in the literature about central nervous system side effects due to acyclovir.

METHODS

Repeated blood samples were drawn in a patient with severe acyclovir overdose who developed coma and nonoliguric renal failure. The acyclovir levels measured by radioimmunoassay were related to the level of consciousness.

RESULTS

We measured the highest acyclovir serum levels reported so far (229.9 mumol/L = 51.8 mg/L). Impairment of consciousness developed with a remarkable temporal delay of 24 to 48 hours after occurrence of peak serum concentrations and resolved with a comparable delay after reaching the therapeutic range (anticlockwise hysteresis). Six days after discontinuation of the drug, central nervous system symptoms had resolved, and, 4 days later, renal function returned to pretreatment values.

CONCLUSIONS

The observation that neurotoxicity developed with a delay of 24 to 48 hours after acyclovir peak serum concentrations could explain the wide range of acyclovir levels reported in similar cases. Single drug level measurements may therefore be of little diagnostic value. Since toxicity develops with a remarkable delay, early removal of the drug (by hemodialysis) could possibly prevent central nervous toxicity.