Pentobarbital, drug form

Barbituric acids as their name implies are weakly acidic and are converted to then-sodium salts (sodium barbiturates) m aqueous sodium hydroxide Sometimes the drug is dispensed m its neutral form sometimes the sodium salt is used The salt is designated by appending the word sodium to the name of the barbituric acid—pentobarbital sodium for example... 

Oxidation reactions can be divided into two kinds those in which oxygen is incorporated into the drug molecule, and those in which primary oxidation causes part of the molecule to be lost The former include hydroxylations, epoxidations, and sulfoxidations. Hydroxylations may involve alkyl substituents (e.g., pentobarbital) or aromatic ring systems (e.g propranolol). In both cases, products are formed that are conjugated to an organic acid residue, e.g., glucuronic add, in a subsequent Phase 11 reaction. 

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. 

Barbiturates are known to form stable inclusion complexes with CDs in aqueous solution. When the stability constants of inclusion complexes of hexobarbital (HBA), thiopental (TPA) and pentobarbital (PBA) with CDs were determined, those with 3-CD were the largest, then with Y-CD next, and with a-CD the smallest for these three drugs (10a). 

Many barbiturates are cyclic amides of barbituric acid that act as sedatives in small dosages or sleep inducers in larger dosages. They are often habit forming. Barbiturate drugs include phenobarbital (Luminal) and pentobarbital (Nembutal). 

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