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30/10/2025, 00:02 Pharmaceutical Solutions & Sterile Dosage Forms
Hydrolysis
It is the breaking of chemical bond (hydrolysable bond as esters and amides) by interaction with
water.
Drugs susceptible to hydrolysis are those containing ester (RCOOR') as aspirin, cyclic esters
(lactones), amide (RCONH₂) as chloramphenicol or cyclic amides (lactams as penicillins).
In addition to water, hydrolysis can be accelerated by pH (acids and bases) and high
temperature. Thus, to avoid hydrolysis:
Adjust pH of the product by using buffers.
Avoid high temperature (keep the product in refrigerator, e.g. chloramphenicol eye drops).
Avoid contact with water. The drug can be reconstituted with water just before use as in case
of antibiotics for oral suspensions or injections (vials).
The resulting loss of drug molecules can reduce the efficacy of the formulation and increase the
drug's toxicity if the products of the chemical changes are toxic.
Oxidation
Oxidation occurs at room temperature can involve O₂ (auto-oxidation) or light (photo-oxidation).
Drugs prone to oxidation are those containing phenolic groups, amino groups, unsaturated
structures, etc.
How to avoid oxidation:
1. To reduce photo-oxidation, solutions are packaged in containers that do not allow light
transmission.
2. To reduce oxidation, antioxidants and/or metal chelators (as heavy metal ions catalyse
oxidation) are used.
3. Packaging: Using opaque, airtight containers to protect from light and oxygen.
4. Oxygen can be excluded, by purging the solution with nitrogen and creating a nitrogen
headspace within the container.
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