Effects of infused norepinephrine and angiotensin-II on vasopressin levels in humans

Angiotensin II (A-II) has been shown to stimulate plasma arginine vasopressin (AVP) secretion in experimental animals, although offsetting effects from a rise in arterial pressure may obscure the effect. A rise in plasma norepinephrine (NE) may have several effects on plasma AVP because of changes in arterial pressure and central adrenergic stimulation. As little data exist concerning these neurohumoral interrelationships in humans, the current investigation was performed to examine the role of acute changes in plasma NE and A-II in the control of arginine vasopressin (AVP). The question is of potential importance because of diffuse disturbances in neurohumoral control in diseases such as hypertension and congestive heart failure. We measured heart rate, arterial pressure, and plasma AVP during 2.5 and 5.0 micrograms/min infusions of NE, and during .05 and .10 micrograms/kg/min infusions of A-II. NE increased mean blood pressure from 81 +/- 11 mm Hg to 87 +/- 16 mm Hg at 2.5 micrograms/min and to 93 +/- 16 mm Hg at 5.0 micrograms/min (p less than .001). Heart rate was unchanged during the 2.5 micrograms/min infusion but declined from 58 +/- 9 beats/min to 54 +/- 9 beats/min during the 5.0 micrograms/min infusion (p = NS). Plasma AVP, 3.0 +/- 0.9 pg/mL, did not change. During A-II infusions, mean arterial pressure increased from 81 +/- 13 mm Hg to 92 +/- 17 mm Hg and 112 +/- 21 mm Hg at the two rates (p less than .001); heart rate declined from 61 +/- 6.8 beats/min to 59 +/- 9.1 beats/min and 56 +/- 11.3 beats/min (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Phenytoin prophylaxis of cardiotoxicity in experimental amitriptyline poisoning

Tricyclic antidepressants (TCA) are drugs with Type IA antiarrhythmic properties that cause severe cardiac conduction blocks, hypotension, and ventricular dysrhythmias at toxic levels. Phenytoin has been proposed as a prophylaxis and treatment of these dysrhythmias, since it is thought to improve conduction in this setting. Anesthetized dogs were given a loading dose of phenytoin, followed by constant amitriptyline infusion until death. Variables known to affect TCA toxicity, such as arterial pH, were carefully controlled. There were no significant differences between the phenytoin and control group in any physiologic parameter, including toxicity, drug levels, or dose to death. However, duration and frequency of episodes of ventricular tachycardia were dramatically increased in the phenytoin group. It is concluded that prophylactic phenytoin in this animal model provides no benefits and may in fact increase the severity of ventricular tachycardia and hypotension. In addition, it is speculated that similar adverse effects of phenytoin might be seen in other Type IA antiarrhythmics if the extremely toxic levels seen in this study with TCA were reached.

Effects of phenylpropanolamine and isometric exercise on blood pressure

The effects of a single dose of phenylpropanolamine (PPA) and isometric handgrip exercise were studied to determine whether the combination increases blood pressure more than either one alone. Six normotensive subjects performed 2 min of exercise at 30 percent of maximal effort before, 1 and 2 h after PPA 37.5 mg (immediate release formulation) or placebo. PPA alone increased the sitting systolic blood pressure at 2 h (PPA 7.2 +/- 8.2 mmHg, placebo - 1.8 +/- 3.4 mmHg, P = 0.016) but did not increase diastolic blood pressure. Handgrip exercise increased systolic and diastolic blood pressures to a similar extent 2 h after PPA (24.0 +/- 8.2/18.3 +/- 7.7 mmHg) or placebo (24.7 +/- 8.2/21.0 +/- mmHg). However, the total increase in systolic blood pressure after PPA + exercise at 2 h (increase in resting blood pressure + increase due to exercise, 31.2 +/- 8.9 mmHg) was greater than after placebo + exercise (22.8 +/- 9.3 mmHg, P = 0.048). These data suggest that the effects of PPA and handgrip exercise on blood pressure are additive. Because the contribution of PPA alone to the blood pressure increase was small and the dose of PPA used was greater than in most over-the-counter formulations, this interaction is probably of limited clinical importance.

Large scale production and purification of paraquat and desipramine monoclonal antibodies and their Fab fragments

We describe the rapid, large scale purification of Fab fragments from mouse monoclonal antibodies. Antibodies against two clinically important and often fatal toxins, paraquat and desipramine, were isolated from mouse ascites fluid by preparative high performance hydroxylapatite (HPHT) or ion exchange (DEAE) high performance liquid chromatography. A competitive inhibition ELISA was used to determine the cross-reactivity of the antibody with analogs of the antigens. Papain digests of the IgGs were subjected to further HPHT followed by Sephadex G-100 chromatography to yield homogeneous Fab fragment preparations. The high purity of these preparations, demonstrated by SDS polyacrylamide gel electrophoresis, has only been achieved previously by affinity chromatography. Intrinsic association constants for the intact IgG and the Fab fragment--antigen interactions, determined by competitive inhibition ELISA, were similar. This indicates that antigen-binding activity was conserved during the production and purification of the Fab fragments.

Pharmacokinetics and toxicity of high doses of antibody Fab fragments in rats

The treatment of drug toxicity with drug-specific antibody fragments may, for some compounds, require very high doses of antibody fragments. To examine the feasibility of this therapeutic approach, the pharmacokinetics and toxicity of high doses of nonspecific human IgG Fab fragments were studied in rats. Six animals received 7.5 g/kg iv Fab over 1 hr. Maximum serum Fab concentration was 42.1 +/- 9.9 mg/ml. Calculated pharmacokinetic parameters included steady state volume of distribution 0.43 +/- 0.06 liter/kg, t/2 alpha 2.4 +/- 1.4 hr, t/2 beta 16.3 +/- 2.4 hr, and systemic clearance 27.2 +/- 4.4 ml/hr/kg. Urinary excretion accounted for 31.8 +/- 7.5% of the administered dose. These values are similar to those previously reported for much lower doses (5-15 mg/kg) of digoxin-specific Fab fragments in dogs, baboons, and humans. All animals tolerated Fab infusion without changes in blood pressure, heart rate, or electrocardiogram. The serum creatinine concentration and urinary protein excretion were unchanged 1 week after Fab administration. One animal developed a self-limited respiratory illness 1 week after Fab administration, probably because of intercurrent infection. Organ histology 2 weeks after Fab administration was normal in all animals. These data suggest that rapid iv administration of high doses of antibody Fab fragments is feasible and support the potential use of high doses of Fab fragments as a therapy for drug toxicity. Although the possibility of dose-dependent kinetics was not studied, the similarity of the pharmacokinetics of this high Fab dose in the rat to that of lower doses in other species further suggests that the rat may be a suitable species for studying Fab-drug interactions.

Myocardial necrosis due to intraperitoneal administration of phenylpropanolamine in rats

Overdose with the sympathomimetic agent phenylpropanolamine (PPA) may cause arrhythmias and myocardial injury in humans. To study the mechanism of these toxic effects, unanesthetized rats (6 animals per group) were given single intraperitoneal doses of 1, 2, 4, 8, 16, or 32 mg/kg PPA. Increases in blood pressure, measured by tail cuff, were dose related and comparable to increases reported in patients with PPA toxicity. Animals were killed at 24 hr and light microscopic examination showed diffuse, dose-related myocardial necrosis. Histology scores (a measure of severity of necrosis) in groups receiving 8, 16, and 32 mg/kg PPA were 1.4 +/- 0.5, 1.8 +/- 1.0, and 2.3 +/- 0.4, respectively, and were all significantly greater than the histology score of control animals (0.2 +/- 0.3, p less than 0.01). The observed lesion was similar in appearance to the myocardial necrosis produced by large doses of catecholamines or sympathomimetic agents in rats. In summary, single doses of PPA caused myocardial necrosis in rats at doses comparable to those causing toxicity in humans. Myocardial necrosis may contribute to the cardiac toxicity of PPA overdose.

Pharmacokinetics and toxicity of high-dose human alpha 1-acid glycoprotein infusion in the rat

The pharmacokinetics of high-dose human alpha 1-acid glycoprotein (AAG) was studied in rats to determine the feasibility of using AAG to alter the tissue distribution of basic drugs. alpha 1-Acid glycoprotein (2.2 g/kg) was administered iv to six male Holtzman rats over a period of 30 min, and serum AAG concentrations were measured by a specific radial immunodiffusion assay. The AAG concentrations were computer fit to a biexponential equation to generate pharmacokinetic constants for an open two-compartment model. The peak serum AAG concentration was 1830 +/- 180 mg/dL at the end of infusion; greater than 20 times the normal value for rats. The central volume of distribution and steady state volume of distribution were 0.09 +/- .02 and 0.15 +/- 0.02 L/kg, respectively. Total body clearance of AAG was 0.065 +/- 0.005 L/kg/h, and the terminal elimination half-life was 19.3 +/- 1.5 h. The AAG administration was tolerated without adverse effect and did not alter systolic blood pressure, the electrocardiogram, creatinine clearance, weight gain, or survival. The results of the histologic examination of various tissues by light microscopy at 30 d post AAG treatment were normal. These data demonstrate that high doses of human AAG can be safely administered to rats and that they produce supraphysiologic serum AAG concentrations.

Physical assessment and differential diagnosis of the poisoned patient

The rapid diagnosis and immediate intervention required in patients with serious drug overdose or poisoning makes toxicological screening of limited value to the emergency department physician. Instead, a careful clinical evaluation using the history, physical examination, and the more readily available laboratory tests may allow a tentative diagnosis and the initiation of life-saving treatment. Laboratory tests should include serum osmolality, electrolytes, glucose, BUN and an estimation of the anion and osmolar gaps. The ECG can also provide useful information. Clinical findings of important include altered blood pressure, pulse, respiration and body temperature, the presence of coma, agitation, delirium or psychosis, and muscular weakness. An ophthalmological examination is also of importance in the acutely poisoned patient. Oral burns or dysphagia may occur following ingestion of any strongly reactive substance, but the absence of oral burns does not preclude the possibility of oesophageal or stomach injury. Odours and skin colour may also contribute to the diagnosis. Comprehensive toxicology screening may not be immediately available, or may be inaccurate, thus adding little to the information obtained during the initial evaluation of the poisoned patient.

Hyperthermia associated with drug intoxication

Hyperthermia (temperature of at least 40.5 degrees C for at least one hour) associated with drug intoxication was identified in 12 patients over a 5-yr period. Intoxication was due to anticholinergic drugs (tricyclic antidepressants, antipsychotics, antihistamines), CNS stimulants (phencyclidine, cocaine, 3,4-methylene dioxyamphetamine, mescaline, lysergic acid diethylamide), salicylates, or combinations of these. Hyperthermia was present in four patients on admission, but its onset was delayed up to 12 h in the remainder. Outcome of hyperthermic patients was poor: five died and four had severe permanent neurologic sequelae. Clinical signs common to patients who developed hyperthermia were increased muscular activity and absence of sweating. Five patients suffered seizures, and four did not respond to anticonvulsant medication until body temperature was lowered. Cooling did not appear to favorably affect the outcome after body temperature had remained above 40.5 degrees C for a prolonged period. Prevention of death or neurologic sequelae from drug-induced hyperthermia depends upon the recognition of risk factors and the prompt treatment of hyperthermia.

Tricyclic antidepressant poisoning. Management of arrhythmias

Deaths from tricyclic antidepressant (TCA) overdose are usually due to arrhythmias and/or hypotension. Tricyclic antidepressant toxicity is due mainly to the quinidine-like actions of these drugs on cardiac tissues. Slowing of phase 0 depolarisation of the action potential results in slowing of conduction through the His-Purkinje system and myocardium. Slowed impulse conduction is responsible for QRS prolongation and atrioventricular block, and contributes to ventricular arrhythmias and hypotension. Therapies that improve conduction, e.g. hypertonic sodium bicarbonate, are useful in treating these toxic effects. Other mechanisms contributing to arrhythmias include abnormal repolarisation, impaired automaticity, cholinergic blockade and inhibition of neuronal catecholamine uptake. Toxicity may be worsened by acidaemia, hypotension or hyperthermia. Sinus tachycardia is due to the anticholinergic effects of the tricyclic antidepressants as well as blockade of neuronal catecholamine reuptake. Sinus tachycardia is generally well-tolerated and requires no therapy. Sinus tachycardia with QRS prolongation may be difficult to distinguish from ventricular tachycardia. Electrocardiograms obtained using oesophageal or atrial electrodes may be useful in determining the relationship of atrial and ventricular activity. Although QRS prolongation alone is not compromising, it is a marker for patients at highest risk of developing seizures, arrhythmias or hypotension. Ventricular tachycardia (monomorphic) is a consequence of impaired myocardial depolarisation and impulse conduction. Hypertonic sodium bicarbonate may partially correct impaired conduction and be of benefit in treating ventricular tachycardia. Since hypertonic sodium bicarbonate appears to act by increasing the extracellular sodium concentration as well as by increasing extracellular pH, hyperventilation may be less effective. Hypertonic sodium bicarbonate is of particular benefit in patients who are acidotic, since acidosis aggravates cardiac toxicity. However, administration of hypertonic sodium bicarbonate is beneficial even when blood pH is normal. Lignocaine (lidocaine) may be useful in treating ventricular tachycardia but should be administered cautiously to avoid precipitating seizures. Ventricular bradyarrhythmias are due to impaired automaticity or depressed atrioventricular conduction and can be treated by placement of a temporary pacemaker, or with a chronotropic agent, e.g. isoprenaline (isoproterenol), with or without concomitant vasoconstrictors.(ABSTRACT TRUNCATED AT 400 WORDS)

Propranolol antagonism of phenylpropanolamine-induced hypertension

Phenylpropanolamine (PPA) overdose can cause severe hypertension, intracerebral hemorrhage, and death. We studied the efficacy and safety of propranolol in the treatment of PPA-induced hypertension. Subjects received propranolol either by mouth for 48 hours before PPA or as a rapid intravenous infusion after PPA. PPA, 75 mg alone, increased blood pressure (31 +/- 14 mm Hg systolic, 20 +/- 5 mm Hg diastolic), and propranolol pretreatment antagonized this increase (12 +/- 10 mm Hg systolic, 10 +/- 7 mm Hg diastolic). Intravenous propranolol after PPA also decreased blood pressure. Left ventricular function (assessed by echocardiography) showed that PPA increased the stroke volume 30% (from 62.5 +/- 20.9 to 80.8 +/- 22.4 ml), the ejection fraction 9% (from 64% +/- 10% to 70% +/- 7%), and cardiac output 14% (from 3.6 +/- 0.6 to 4.1 +/- 1.0 L/min). Intravenous propranolol reversed these effects. Systemic vascular resistance was increased by PPA 28% (from 1710 +/- 200 to 2190 +/- 700 dyne X sec/cm5) and was further increased by propranolol 22% (to 2660 +/- 1200 dyne X sec/cm5). We conclude that PPA increases blood pressure by increasing systemic vascular resistance and cardiac output, and that propranolol antagonizes this increase by reversing the effect of PPA on cardiac output. That propranolol antagonizes the pressor effect of PPA is in contrast to the interaction in which propranolol enhances the pressor effect of norepinephrine. This is probably because PPA has less beta 2 activity than does norepinephrine.

Fatal acute selenium toxicity

Selenium is used widely in industry and as a dietary supplement. Reports of acute selenium toxicity are infrequent, however, and the relationship of toxicity to selenium concentrations in blood and tissues has not been established. We describe a patient who died eight days after ingesting selenious acid in the form of gun blueing. The patient's clinical course demonstrated many of the features of inorganic selenium toxicity described in animals; hypotension as a result of both vasodilation and decreased cardiac output, adult respiratory distress syndrome, severe myopathy which contributed to respiratory failure, and a garlicky odor to the breath. Four days after ingestion the serum selenium concentration was twenty times normal and urinary excretion seventy times normal. Postmortem tissue selenium concentrations were up to 40 times normal.

Therapeutic doses of phenylpropanolamine increase supine systolic blood pressure

The anorectic agent phenylpropanolamine (PPA) has a low therapeutic index and can cause severe hypertension at doses as low as 85 mg. To determine the effects of a therapeutic dose on blood pressure, PPA 37.5 mg (as a commercially available immediate release formulation) or placebo was administered orally to ten normotensive subjects using a randomized double-blinded crossover design. The mean increase in supine systolic blood pressure (BP) was greater after PPA (18.5 +/- 10.7 mmHg) than after placebo (5.1 +/- 5.4 mmHg, P = 0.005). Increases in systolic BP after PPA ranged from 8 to 43 mmHg. The BP increase due to PPA was postural, and there was no change in sitting or standing BP. Doses of PPA available in over-the-counter formulations can increase supine systolic BP. Recent use of products containing PPA should be considered when evaluating patients with hypertension.

Toxicity of over-the-counter stimulants

Over-the-counter stimulants (phenylpropanolamine hydrochloride, ephedrine, pseudoephedrine, caffeine) are used widely as decongestants, anorectic agents, amphetamine substitutes, and "legal stimulants." Toxic effects may result from overdose, drug interactions, or diseases that increase sensitivity to sympathomimetic agents. The most important toxic effect of the alpha-adrenergic agonist phenylpropanolamine is hypertension, which may result in hypertensive encephalopathy or intracerebral hemorrhage. The therapeutic index of phenylpropanolamine is low, and severe hypertension may occur after ingestion of less than three times the therapeutic dose. Ephedrine and pseudoephedrine may also cause hypertension, as well as tachyarrhythmias due to beta-adrenergic stimulation. Toxic reactions from caffeine are characterized by agitation, seizures, tachyarrhythmias, and hypotension. Management of toxic reactions to over-the-counter stimulants includes control of hypertension with a rapidly acting vasodilator, beta-blockers for tachyarrhythmias, and control of seizures.

Pharmacokinetic and pharmacodynamic considerations in drug therapy of cardiac emergencies

In the drug therapy of cardiac emergencies, it is necessary to rapidly achieve therapeutic drug concentrations and adjust drug dose as the patient's clinical status changes. Cardiac dysfunction is often present and may alter drug pharmacokinetics. Circulatory failure causes sympathetically mediated vasoconstriction in most tissues, with relative sparing of the brain and heart due to autoregulation. Blood flow to vasoconstricted tissues is reduced, and the available cardiac output is redistributed so that the heart and brain receive a greater fraction. Drug distribution to tissues is therefore slowed, and the initial concentration of drug in blood is higher when circulatory failure is present than when it is absent. This higher blood concentration is reflected by higher concentrations of drug in the brain and heart, which are relatively well perfused. Initial doses of many drugs need to be reduced in patients with circulatory failure to prevent cardiac or central nervous system toxicity. Cardiac output is markedly diminished during cardiopulmonary resuscitation (CPR), but blood flow distribution is qualitatively similar to that of circulatory failure with spontaneous circulation. Pneumatic trousers increase lower extremity vascular resistance and may produce a similar redistribution of blood flow. Drug distribution during the use of CPR or pneumatic trousers should be similar to that of circulatory failure with spontaneous circulation, but few data are available to guide drug dosing during the use of these interventions. Animal data suggest that the central volume of distribution of some drugs during CPR may be as small as one-tenth of normal. Drug metabolism in circulatory failure may be impaired by reduced hepatic blood flow resulting in decreased clearance of highly extracted drugs, or by hepatocellular dysfunction resulting in decreased clearance of poorly extracted drugs. Drug excretion may be impaired by reduced renal blood flow resulting in decreased filtration or secretion and increased reabsorption. The maintenance dose of many drugs must therefore be reduced in the presence of circulatory failure. Intravenous drug administration is preferred in patients with circulatory failure. The central intravenous route is often convenient but must be used cautiously when administering potentially cardiotoxic drugs. Intratracheal administration appears to be a promising alternative for some drugs, such as adrenaline (epinephrine). Intracardiac injections are hazardous and offer no demonstrated advantage over other routes.(ABSTRACT TRUNCATED AT 400 WORDS)

Efficacy and mechanism of action of sodium bicarbonate in the treatment of desipramine toxicity in rats

Alkalinization of the blood by administration of sodium bicarbonate or hyperventilation is widely recommended for treatment of cardiac toxicity due to tricyclic antidepressant overdose, yet its efficacy and mechanism of action are poorly defined. We studied the effects and possible mechanism of action of 1 M NaHCO3 on desipramine (DMI) toxicity in anesthetized, paralyzed rats. Administration of DMI (45 mg/kg i.p.) produced a mean increase in QRS duration of 142% and a mean decrease in mean arterial pressure of 46%. Treatments were administered i.v. 35 min after DMI and their effects were assessed 10 min later. NaHCO3 (1 M) at doses of 3 and 6 mEq/kg decreased mean QRS duration 15 +/- 5 and 24 +/- 6%, respectively (mean +/- S.D.) and was superior to no treatment (P less than .01). NaCl (1 M) was as effective as NaHCO3 in decreasing QRS duration, as was 1 M NaHCO3 supplemented with 48 mM KCl. Respiratory alkalosis and 10% mannitol did not decrease QRS duration. NaHCO3, NaCl and NaHCO3/KCl all produced comparable increases in mean arterial blood pressure. Respiratory alkalosis and mannitol did not increase mean arterial pressure, but did prevent the decline seen in control animals. Acidosis produced by ventilation with 10% CO2 exacerbated QRS prolongation due to DMI. In acidotic animals, NaHCO3 and NaCl were equally effective in reversing QRS prolongation and hypotension. Correction of respiratory acidosis by discontinuation of inhaled CO2 did not improve QRS duration or mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemoperfusion for imipramine overdose: elimination of active metabolites

The serum concentrations of imipramine and its pharmacologically active metabolites were followed during resin hemoperfusion for imipramine overdose. The initial serum concentration of 2-hydroxy-imipramine plus 2-hydroxy-desipramine was 13.3% of the total tricyclic antidepressant level (imipramine + desipramine + hydroxymetabolites). Despite high extraction ratio (greater than or equal to 0.75) and clearances (130--180 mL/min) for both imipramine and its metabolites, the calculated amount of drug removed was small. Only 0.91% of the estimated dose ingested was removed as imipramine, 0.52% as desipramine, and 0.33% as hydroxylated metabolites. While the hydroxylated metabolites of imipramine may contribute to its toxicity, it is unlikely that the small amount removed can explain reports of apparent clinical benefit from hemoperfusion.