Volume 6 | Issue 4 Article 7 1944 Barbiturates I. E. Peterson Iowa State College Follow this and additional works at: https://lib.dr.iastate.edu/iowastate_veterinarian Part of the Veterinary Toxicology and Pharmacology Commons Recommended Citation Peterson, I. E. (1944) "Barbiturates," Iowa State University Veterinarian: Vol. 6 : Iss. 4 , Article 7. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol6/iss4/7 This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. Barbiturates Their applicatiolls to veterinary therapeutics I. E. Peterson, '44 URING the last decade, a new group The barbiturates may be generally clas­ D of drugs, known as the barbiturates, sified as long or short acting, and the two has come into prominence in veterinary groups should not be used interchange­ medicine as hypnotics and anesthetics. ably. The choice of drug to be used de­ Today we find that these derivatives of pends on the type of patient, length of barbituric acid are used quite extensively time and rapidity of action desired, con­ in human medicine and in the small ani­ dition of the patient, and history of pre­ mal field of veterinary medicine. The vious medication. The barbiturates are therapeutic action of the derivatives of destroyed mostly in the liver and are ex­ this parent barbituric acid molecule, which creted to a certain extent by the kidneys. is weakly acid but has no sedative or In toxic doses, the respiratory system is hypnotic effect, has been made possible affected more quickly than is the cardiac because one or both of the hydrogens on system, but in animals which have a cir­ the side chains are replaceable. Thus, culatory disturbance, the barbiturates af­ barbital or diethyl barbituric acid was fect the heart and blood pressure even in obtained by replacing each hydrogen with light doses before the respiratory system an ethyl radical, forming a derivative shows any effects of overdosage. In gen­ which did possess hypnotic and sedative eral, the contraindications of the barbitu­ action. Similarly, by replacing one hydro­ rates are hepatic disease, renal impair­ gen with an ethyl radical and the other ment, circulatory disturbances, acidosis, with a phenyl radical, phenyl ethyl bar­ anemia, respiratory distress from any bituric acid or phenobarbital, was ob­ cause, toxemia, shocks, and previous ad­ tained. This had twice the potency of bar­ ministration of other sedatives, hypnotics, bital, yet possessed no greater toxicity. or anesthetics in large doses. Especially Further chemical research with barbituric those patients showing toxemia or shock acid produced pentobarbital or nembutal, should be watched very closely during by substituting an ethyl radical for one administration of the barbiturates for any hydrogen and a methyl-butyl group for idiosyncrasy to the drug. The barbiturates the other. This drug was not used phar­ are not usually considered to be habit macologically or clinically for many years forming in humans, but a few cases of this after it was first synthesized. An isomer occurrence have been reported. of pentobarbital called amytal, which had greater hypnotic effect, more rapid action, Advantages and faster elimination than pentobarbital, was produced by Shonle in 1920. The so­ The advantages of barbiturates are dium salts of these barbituric acid deriva­ enumerated as follows: tives were later shown to be more soluble 1. The degrees of action may be easily and more adapted to intravenous and in­ graded from very slightly sedative to com­ tramuscular injection, thus giving quicker plete anesthesia. and deeper, but shorter, effects. 2. The effect is very prompt, within a 198 The Veterinary Student few minutes after oral doses and imme­ and benezdrine sulfate. Picrotoxin seems diately after intravenous. to be quite superior due to its lasting ef­ 3. Full doses cause little effect on other fect but all of them must be given in re­ functions. peated dosage since they are eliminated 4. The respiratory system, circulation, from the body more quickly than the bar­ metabolism, and smooth muscle remain biturates. These should be supplemented almost normal until full toxic doses are by injections of hypertonic dextrose solu­ reached. tion and artificial respiration. The bar­ 5. Most of them have no serious after­ biturates have been used for euthanasia effects. in large doses to small animals and the 6. They produce no serious local ef­ younger large animals. The use for this fects so they may be administered by all purpose has been limited due to the cost channels. compared to that of saturated magnesium The disadvantages of the barbiturates sulfate solution. The barbiturates produce are the following: death without violent struggling as is 1. The response to the drug is not al­ seen in many other products used for this ways the same. purpose and thus are quite humane. 2. The hypnotic action is sometimes preceded by excitement, which is the rea­ Classification son for using a small dose of morphine in dogs before administering the barbitu­ The barbiturate drugs fall into two rates. general classifications, the short acting 3. As anesthetics they are administered group and slow acting group. The short at a single dose, thus making for error in acting group includes pentothal sodium, the concentration in the body, and they seconal sodium, pentobarbital sodium, require much safer handling when used amy tal, and sodium amy tal. This group for general anesthesia than when used as produces anesthesia very rapidly but is basal narcotics. short acting due to the rapid elimination 4. They require too large dosage and of the drug from the body. are therefore too expensive in large ani­ Pentothal sodium, or sodium ethyl thio­ mal practice. barbituric acid, is one of a series of new thiobarbiturates. It is rapidly destroyed Indications in the body, and although it is rapid in effect the duration of this effect is rela­ The barbiturates in general are indi­ tively short. It is an excellent anesthetic cated for the following conditions: for minor operations in small animals for 1. As a sedative in nervous conditions, the effect may be gone in 20 to 30 minutes. 2. As an analgesic in neuritis and pru­ The solution should be freshly made and ritis, slowly administered, a careful check be­ 3. To control nausea and vomiting, ing kept on the dose as injection proceeds. 4. As a motor depressant in convulsive When anesthesia is sufficiently advanced, states as in epilepsy, Glclampsia, and strych­ injection must cease; when the patient is nine poisoning, unconscious and respiration is shallow, 5. Preliminary to local anesthetics to anesthesia is usually present. The onset prevent accidents with cocaine and pro­ of anesthesia is usually so rapid that the caine, normal stages of anesthesia cannot be 0 b­ 6. As preanesthetic narcotic, and served during the administration of this 7. As anesthetics. drug. The dosage varies in different ani­ In poisoning with these drugs, respira­ mals; 7.0 to 11.0 mg. per pound body tory stimulants are used. The following weight injected intravenously with a drugs have been used as antidotes: picro­ standard dose of 10.0 mg. per pound of toxin or metrazol with ephedrine, picro­ body weight as an average is recom­ toxin, metrazol, ephedrine, coramine, mended. The anesthesia will persist for icoral, strychnine, caffeine, dinitrophenol, 25 to 30 minutes when an average dose of Spring, 1944 199 pentothal sodium is injected following the intramuscular inejction. The 5 percent administration of 8 to 32 mg. of morphine weight-volume solution is prepared with and 0.4 to 0.6 mg. of atropine to dogs. sterile water in the ampoule for this pur­ Seconal sodium has been used in human pose. Discard any solution of this drug medicine much more extensively than in which exhibits slight opalescence or hazi­ veterinary medicine. However, it is of ness. some value as a hypnotic when given in Pentobarbital sodium in preanesthetic small repeated doses to small animals for medication has many advantages similar the period of recovery is much shorter to those of sodium amy tal in which it re­ than that of the longer acting barbiturates. lieves preoperative apprehension by the This drug causes less renal disturbance patient, affords more quiet induction of than other members of the short acting anesthesia, reduces the amount of general group, thus being indicated in those pa­ anesthetic required, and diminishes the tients in which pentobarbital sodium postoperative nausea and vomiting in small would have a detrimental effect on the animals. In comparison to sodium amytal renal system. There are no after effects in preanesthetic medication, only one-half following the administration of this drug. the dose need be used to produce the same It has a large margin of safety in dosage effect and the period of postoperative re­ but larger doses seem to produce restless­ covery is only about one-half as long as ness rather than the desired hypnosis. that following the use of sodium amy tal. This drug is recommended for preanes­ Overdosage of either drug will produce thetic medication in small animals. The respiratory distress and postoperative rest­ dosage is usually 48 mg. to cats and small lessness, so one must caution against use dogs. Large doses followed by toxic re­ of barbiturates in doses sufficient to pro­ actions of the drug may be counteracted duce a deep preanesthetic effect for such by injection of hypertonic dextrose with doses predispose to respiratory embarrass­ caffeine and ephedrine. ment especially when they are supple­ mented with ether to the point of full Nembutal anesthesia.