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30/10/2025, 00:02 Pharmaceutical Solutions & Sterile Dosage Forms
pH adjustment
Most existing drugs are either weak acids or weak bases (ionizable drugs).
Since ions are more soluble in water than neutral molecules, changing the pH of the medium to
increase ionization of the drug is a common technique for increasing drug solubility in an
aqueous medium.
Weakly acidic drugs are ionized when the pH of the solvent is increased. Conversely, lowering pH
favors ionization of weakly basic drugs.
pH can be adjusted using acids or alkali or using buffers.
Extremes of pH should be avoided so that the solution is physiologically acceptable.
The chosen pH should not adversely affect the stability of the drug and excipients (e.g.
inactivation of acidic preservatives by ionization).
Bioavailability of the drug should also not be compromised by a change in pH (the
unionized form of the drug is more absorbed than ionized one through biological
membranes).
The pH of a pharmaceutical solution is thus a compromise between drug solubility, stability 12/77
and bioavailability, the function of excipients, and physiological acceptability of the
product.
Complexation
Cyclodextrins (CDs) are cyclic glucose-based oligosaccharides.
o There are 3 types of depending on the number of d-glucopyranosyl units in the ring
structure.
o Alpha: 6 units
• Beta: 7 units
• Gamma: 8 units
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