Barbiturates toxicity

Treatment of barbiturate toxicity is mainly supportive (ie, maintaining a patent airway, oxygen administration, monitoring vital signs and fluid balance). The patient may require treatment for shock, respiratory assistance, administration of activated charcoal, and in severe cases of toxicity, hemodialysis. 

The onset of symptoms of barbiturate toxicity may not occur until several hours after the drug is administered. Symptoms of acute toxicity include CNSand respiratory depression, constriction or paralytic dilation of the pupils tachycardia, hypotension, lowered body temperature, oliguria, circulatory collapse, and coma. The nurse should report any symptoms of toxicity to the primary health care provider immediately. 

Acute barbiturate toxicity is characterized by automatism, or a state of drug-induced confusion, in which patients lose track of how much medication they have taken and take more. Death results from respiratory failure. The treatment of poisoning consists of supporting the respiration, preven-... 

The incidence of side effects is low. but the drug should be used with caution, if at all. in patients with impaired hepatic function. Similarly, patients taking barbiturates concurrently with the drug should be ob.served carefully, in view of reports of barbiturate toxicity under these circutastances. 

There is a broad spectrum of signs and symptoms associated with acute short-acting barbiturate toxicity. Lethargy, ataxia, nystagmus, diplopia, amnesia, slurred speech, confusion, hypotonia, hypotension, hypothermia, hypoglycemia, coma, respiratory depression, and death have been reported. Comatose patients may develop erythematous or hemorrhagic bullous skin lesions primarily over areas of pressure (e.g., elbows and knees). These lesions are commonly referred to as barb burns . Doses of 3-5 mg kg of most short-acting barbiturates will cause toxicity in children. The estimated potentially fatal dose in nondependent adults is 3-6 g. 

Acute intoxication resembles barbiturate toxicity. Clinical effects include dose-related central nervous system depression, nystagmus, ataxia, nausea and vomiting, dizziness, vertigo, and irritability. 

Acute barbiturate toxicity is characterized by automatism, or a state of drug-induced confusion, in which patients lose track of how much medication they have taken and take more. Death results from respiratory failure. The treatment of poisoning consists of supporting respiration, prevention of hypotension, as well as diuresis, hemodialysis and, in the event of phenobarbital poisoning, the administration of sodium bicarbonate. Tolerance does not develop from lethal doses. The abrupt withdrawal from barbiturates may cause tremors, restlessness, anxiety, weakness, nausea and vomiting, seizures, delirium, and cardiac arrest. 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

Phenytoin. Phenytoin sodium is sodium diphenylhydantoin [630-93-3] which is stmcturally related to the barbiturates. It was originally introduced as an anticonvulsant (18) (see Hypnotics, sedatives, and anticonvulsants) and later found to have antiarrhythmic properties (19), although not approved by the PDA for any arrhythmic indications. Phenytoin is effective in the treatment of ventricular arrhythmias associated with acute MI and with digitalis toxicity (20). It is not very effective in treatment of supraventricular arrhythmias (20). 

Acetaminophen may alter blood glucose test results, causing falsely lower blood glucose values. Use with the barbiturates, hydantoins, isoniazid, and rifampin may increase the toxic effects and possibly decrease the therapeutic effects of acetaminophen. The effects of the loop diuretics may be decreased when administered with acetaminophen. Hepatotoxicity has occurred in chronic alcoholics who are taking moderate doses of acetaminophen. 

MONITORING AND MANAGING RESPIRATORY DEPRESSION These drugs depress the CNS and can cause respiratory depression. The nurse carefully assesses respiratory function (rate, depth, and quality) before administering a sedative, Vs, to 1 hour after administering the drug, and frequently thereafter. Toxic reaction of the barbiturates can cause severe respiratory depression, hypoventilation, and circulatory collapse. 

When two antiarrhythmic dragp are administered concurrently the patient may experience additive effects and is at increased risk for drug toxicity. When quinidine and procainamide are administered with digitalis, tiie risk of digitalis toxicity is increased. Hiarmacologic effects of procainamide may be increased when procainamide is administered with quinidine When quinidine is administered with the barbiturates or cimetidine, quinidine serum levels may be increased. When quinidine is administered with verapamil, there is an increased risk of hypotensive effects. When quinidine is administered with disopyramide, there is an increased risk of increased disopyramide blood levels and/or decreased serum quinidine levels. 

Death from overdose of barbiturates may occur and is more likely when more than 10 times the hypnotic dose is ingested. The barbiturates with high lipid solubility and short half-lives are the most toxic. Thus the lethal dose of phenobarbital is 6—10 g, whereas that of secobarbital, pentobarbital, or amo-barbital is 2-3 g. Symptoms of barbiturate poisoning include CNS depression, coma, depressed reflex activity, a positive Babinski reflex, contracted pupils (with hypoxia there may be paralytic dilation), altered respiration, hypothermia, depressed cardiac function, hypotension, shock, pulmonary complications, and renal failure. 

Despite the work of Overton and Meyer, it was to be many years before structure-activity relationships were explored further. In 1939 Ferguson [10] postulated that the toxic dose of a chemical is a constant fraction of its aqueous solubility hence toxicity should increase as aqueous solubility decreases. Because aqueous solubility and oil-water partition coefficient are inversely related, it follows that toxicity should increase with partition coefficient. Although this has been found to be true up to a point, it does not continue ad infinitum. Toxicity (and indeed, any biological response) generally increases initially with partition coefficient, but then tends to fall again. This can be explained simply as a reluctance of very hydrophobic chemicals to leave a lipid phase and enter the next aqueous biophase [11]. An example of this is shown by a QSAR that models toxicity of barbiturates to the mouse [12] ... 

OWENS has prepared antibodies to PCP in goats. When administered to mice the PCP levels in blood rose tenfold as an antibody-bound form that was readily excreted in urine. BROWNE tested the selfadministration by rats of 1,000 compounds related (and not related) to PCP, some of which produced PCP-like effects. One compound that was self-administered prevented the entrance of PCP into brain. BALSTER gave a general review of the effects produced by PCP in laboratory animals and showed that some effects were similar to those produced by amphetamine, some to barbiturates, and some to antipsychotics. This response profile makes PCP a unique drug that stands alone in its complex effects and toxicity. 

Superheated water at 100°-240 °C, with its obvious benefits of low cost and low toxicity, was proposed as a solvent for reversed-phase chromatography.59 Hydrophobic compounds such as parabens, sulfonamides, and barbiturates were separated rapidly on poly(styrene-divinyl benzene) and graphitic phases. Elution of simple aromatic compounds with acetonitrile-water heated at 30°-130 °C was studied on coupled colums of zirconia coated with polybutadiene and carbon.60 The retention order on the polybutadiene phase is essentially uncorrelated to that on the carbon phase, so adjusting the temperature of one of the columns allows the resolution of critical pairs of... 

It is probably best to avoid p-methoxyamphetamine (PMA) and 2,5-dimethoxy-4-methylamphetamine (STP), the former because it seems to have a high toxicity and the latter because it lasts too long (e.g., 24 hours for a minimum dose). Other 4-alkyl amphetamines also seem to be toxic. A number of apparent fatalities due to MDA have been noted, but the reports usually involve very large amounts, often in combination with other drugs (e.g., 7 g MDA plus barbiturates) and screening for other, more toxic drugs (in particular, PMA) has not been done. 

Many CNS depressants have some liability for dependence. This is typically greater with barbiturates, but lesser with benzodiazepines, and perhaps nonexistent in many antiseizure medications. CNS depressants produce tolerance when administered chronically, where increasingly larger doses are required to sustain the same level of effect. Further, a cross-tolerance often develops, where the tolerance is generalized to other CNS depressants. For example, a person with an ethanol tolerance will also display some tolerance to barbiturates. The therapeutic index tends to decrease as tolerance increases, so that the difference between an effective and toxic dose diminishes. Thus, tolerance to CNS depressants is accompanied by a smaller safety margin. 

Barbiturates. The hrst barbiturate, barbital, was introduced in 1903 and was followed a few years later by phenobarbital. The barbiturates effectively relieve anxiety, but they are never used as anxiolytics today due to toxicity and abuse concerns. However, several barbiturates, including phenobarbital (Luminal), secobarbital (Seconal), and pentobarbital (Nembutal), remain available and are occasionally used to treat epilepsy and rarely to manage acute alcohol withdrawal. 

Cyclobarbitone. Use the intermediate directly above in the formula for Barbitone. This drug is less toxic than most barbiturates and side effects are seldom encountered. It is quite powerful as far as barbiturates go. Dosage is 100 to 200 mg ( /i to 3 grains), 400 mg maximum, mp 173-... 

Carbromal (Uradal, Adalin.) 1 mole of a-bromo-a-ethyl butyryl bromide is mixed with dry urea (1 mole) and heated on a steam bath for several hours. Precautions must be taken to keep steam and atmospheric H2O from the reaction vessel. Cool, allow to solidify, wash with H2O, and recrystallize from alcohol. Dose (sedative) 300 to 500 mg, (hypnotic) 700 to 950 mg, mp 116-118°. This drug is less potent than the barbiturates, but it is less toxic, extremely well tolerated, has a wide margin of safety, and acts rapidly. 

Since GABA-ergic synapses are confined to neural tissues, specific inhibition of central nervous functions can be achieved for instance, there is little change in blood pressure, heart rate, and body temperature. The therapeutic index of benzodiazepines, calculated with reference to the toxic dose producing respiratory depression, is greater than 100 and thus exceeds that of barbiturates and other sedative-hypnotics by more than tenfold. Benzodiazepine intoxication can be treated with a specific antidote (see below). 

Harger RN, Hulpieu HR Toxicity of tetramethyl succinonitrile and the antidotal effects of thiosulphate, nitrile and barbiturates. Fed Proc 8(abst) 205, 1949... 

Toxic symptoms may be dose-dependent and merely an exaggeration of the therapeutically desirable response, e.g., the coma of barbiturate overdosage and persistence of muscular paralysis after succinylcholine administration, or an unpredictable effect of the drug upon an organ or tissue remote from that upon which the therapeutic effect is manifested. 

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