Phenobarbital sodium injection

ABSORPTION, FATE, AND EXCRETION For sedative-hypnotic use, the barbiturates usually are administered orally (Table 16-3) absorption is rapid and nearly complete. The onset of action varies from 10-60 minutes, depending on the agent and the formulation, and is delayed by the presence of food in the stomach. When necessary, intramuscular injections of solutions of the sodium salts should be placed deeply into large muscles to avoid the pain and possible necrosis that can result at more superficial sites. The intravenous route usually is reserved for the management of status epilepticus (phenobarbital sodium) or for the induction and/or maintenance of general anesthesia (e.g., thiopental or methohexital). 

In rabbits under light amytal anesthesia, chlordan has no direcr effect on the blood pressure, but produces a type of respiration having many characteristics in common with Cheyne-Stokes type. The generalized tremors, opisthotonus, tonic and clonic convulsions, produced by chlordan were decreased or abolished and respiration restored to normal by suitable injections of the sodium salts of amytal, phenobarbital, and pentothal. The LD60 of chlordan, which was about 20 mg. per kg. on intravenous administration to intact rabbits, was increased to about 60 mg. per kg. through the antidotal action of the barbiturates. An unidentified chlorine-containing degradation product with acidic properties was recovered from the urine of rabbits treated with chlordan. Approximately one third of its chlorine content was set free on hydrolysis at 100° C. with sodium hydroxide in either absolute alcohol or in water. 

Oral 50, 100 mg capsules 4 mg/mL elixir Rectal 30, 60, 120, 200 mg suppositories Parenteral 50 mg/mL for injection Phenobarbital (generic, Luminal Sodium)... 

When utilized as sedative hypnotics, barbiturates are administered orally. They are rapidly and completely absorbed by this route with nearly 100% bioavailability and an onset of action ranging from 10 to 60 min.3 Sodium salts are more rapidly absorbed than free acids. Intramuscular injections of sodium salts should be made deep into the muscle to prevent pain and tissue damage. Some barbiturates are also administered rectally barbiturates utilized for the induction and maintenance of anesthesia (thiopental) or for treating status epilepticus (phenobarbital) are administered intravenously. 

Clinically, 0.2 g of phenobarbital or 0.6 g of sodium barbital may be administered an hour before operation. Barbiturates do not prevent the direct circulatory collapse and depression of respiration that occur on intravenous injection of procaine, and are useless or harmful for either prophylaxis or treatment if the anesthetic agent is rapidly absorbed. However, if the symptoms develop slowly, the suppression of the convulsions is at least helpful. 

Fig. 5-32. Separation of various barbiturates. — Separator column IonPac NS1 (10 pm) eluent 0.005 mol/L sodium octanesulfonate + 0.05 mol/L KH2P04 (pH 4.0) / acetonitrile (64 36 v/v) flow rate 1 mL/min detection UV (220 nm) injection volume 50 pL solute concentrations 10 ppm barbital, phenobarbital, and hexobarbital.

In the solid (crystalline) form the barbituric acid exists in the triketo or lactam form. In aqueous solution tautomerism to the enolic lactim occurs the enolic hydroxyl (at C-2) is acidic acid and is ionized according to the particular drug s pKa (e.g., pentobarbital = 8.0, phenobarbital = 7.5). Titrating such a solution with a stoichiometric equivalent of base such as NaOH will convert the lactam quantitatively to the barbiturate s sodium salt, which can be isolated. Many barbiturates are commercially produced both in the lactam and in the sodium enolate salt form. Of course, the salts are water soluble and thus are used to formulate injectable dosage forms including those for IV anesthetic use. 

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