Certain functional groups in drug molecules are prone to chemical
degradation. Drugs with an ester functional group are easily hydrolysed;
e.g., aspirin is easily hydrolysed to salicylic acid. Similarly, many drug
molecules are susceptible to oxidation because of certain oxidizable functional groups, e.g. alcohol.
OCOCH 3
CO 2 H
OH
CO 2 H
Aspirin
Salicylic acid
Hydrolysis
Insulin is a protein and contains amide linkages, which makes this
compound unstable in acidic medium, and unsuitable for oral administration. Like any other proteins in the gastrointestinal tract, insulin is reduced
to its amino acid components, and the activity is totally lost. Many drugs
having olefinic double bonds exhibit trans–cis isomerism in the presence of
light. Similarly, because of the presence of certain functional groups or the
chemical structure, a drug can be sensitive to heat. Many monoterpenyl or
sesquiterpenyl drugs are unstable at high temperatures.
Recommended further reading
Clayden, J., Greeves, N., Warren, S. and Wothers, P. Organic Chemistry, Oxford University
Press, Oxford, 2001.
RECOMMENDED FURTHER READING
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