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A drug is considered highly soluble when the highest dose strength is soluble in 250 ml or less of aqueous media over the pH range of 1 to 6.8. The volume estimate of 250 ml is derived from typical bioequivalence study protocols that prescribe administration of a drug product to fasting human volunteers with a glass of water.
Anhydrous forms often dissolve faster but sometimes are less soluble. Esterification is also used to control solubility. For example, stearate and estolate esters of drugs have decreased solubility in gastric fluid. Later, esterases in the gastrointestinal tract (GIT) wall and blood hydrolyze these esters to release the parent drug.
Therefore, the chemical characteristics of a drug will determine its distribution within an organism. For example, a liposoluble drug will tend to accumulate in body fat and water-soluble drugs will tend to accumulate in extracellular fluids. The volume of distribution (V D) of a drug is a property that quantifies the extent of its distribution ...
Conversely, hydrophilic drugs (low octanol/water partition coefficients) are found primarily in aqueous regions such as blood serum. [ 4 ] If one of the solvents is a gas and the other a liquid, a gas/liquid partition coefficient can be determined.
A V D greater than the total volume of body water (approximately 42 liters in humans [5]) is possible, and would indicate that the drug is highly distributed into tissue. In other words, the volume of distribution is smaller in the drug staying in the plasma than that of a drug that is widely distributed in tissues. [6]
Freebasing also tends to remove water-soluble impurities and adulterants such as sugars (lactose, sucrose, glucose, mannitol, inositol), which are often added to street cocaine. Cocaine freebase is only slightly soluble in water (1 in 600 of water) as compared to the high solubility of cocaine hydrochloride (1 in 0.5 of water). [3]
It is practically insoluble in water whereas hydrochloride salt is water-soluble. Smoking freebase cocaine has the additional effect of releasing methylecgonidine into the user's system due to the pyrolysis of the substance (a side effect which insufflating or injecting powder cocaine does not create).
A cosolvent miscible in both phases and able to dissolve the solute is added to form a homogeneous solution of water, organic solvent, and compound (right). In chemistry, cosolvents are substances added to a primary solvent in small amounts to increase the solubility of a poorly-soluble compound.