SYNTHETIC CORTICOSTEROIDS
Glucocorticoids have
become important agents for use in the treat-ment of many inflammatory,
immunologic, hematologic, and other disorders. This has stimulated the
development of many synthetic steroids with anti-inflammatory and
immunosuppressive activity.
Pharmaceutical
steroids are usually synthesized from cholic acid obtained from cattle or
steroid sapogenins found in plants. Further modifications of these steroids
have led to the marketing of a large group of synthetic steroids with special
characteristics that are pharmacologically and therapeutically important (Table
39–1; Figure 39–3).
The metabolism of the
naturally occurring adrenal steroids has been discussed above. The synthetic
corticosteroids (Table 39–1) are in most cases rapidly and completely absorbed
when given by mouth. Although they are transported and metabolized in a fashion
similar to that of the endogenous steroids, important differences exist.
Alterations in the
glucocorticoid molecule influence its affinity for glucocorticoid and
mineralocorticoid receptors as well as its protein-binding affinity, side chain
stability, rate of elimination, and metabolic products. Halogenation at the 9
position, unsatura-tion of the 1–2 bond of the A ring, and methylation at the 2
or 16 position prolong the half-life by more than 50%. The 1 com-pounds are
excreted in the free form. In some cases, the agent given is a prodrug; for
example, prednisone is rapidly converted to the active product prednisolone in
the body.
The actions of the
synthetic steroids are similar to those of cortisol (see above). They bind to
the specific intracellular receptor pro-teins and produce the same effects but
have different ratios of glucocorticoid to mineralocorticoid potency (Table
39–1).
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