In these days of ever-increasing health-care costs, the cost of prescription drugs - and the cost differential between brand-name and generic versions of the same prescription agents - are a major focus of discussion.

To obtain FDA permission to market a new generic pharmaceutical product, a manufacturer must, during development of the product, conduct appropriate, stringent bio-availability studies in humans and submit reports of the results to that agency.Bio-availability studies involve determining volunteers' blood levels of a product's active ingredient at pre-selected times after the volunteers have ingested either the generic preparation or the original, trademarked preparation.

The shapes of the blood-level curves must be virtually identical for the FDA to approve the marketing of the generic version.

In addition, the manufacturer must demonstrate that the generic's shelf life is similar to that of the original preparation - that is, after production and/or distribution, the pharmacologic potential of the generic product under normal storage conditions will not decrease more quickly than will the pharmacologic potential of the trademarked product. Of course, manufacturers of generics must comply with the same regulations that the FDA applies to manufacturers of trademarked drugs.

What, then, are the differences between trademarked and generic versions of the same pharmaceutical agent in use against the same disease?

The primary difference is that the manufacturer of the trade-marked pharmaceutical must charge enough for it to recoup the money invested in the research and development that led to the patent.

Because the generic-drug manufacturer's research and development expenses are considerably less, that manufacturer can afford to market its generic version at a lower price. Some major pharmaceutical manufacturers market both trademarked and generic lines of products, in which case brand names and generics alike undergo the same processing by the same employees using the same raw materials. They would therefore differ only in labeling - and price.

Are all generic pharmaceuticals identical to their trademarked counterparts? Probably not. There certainly have been instances of generic-drug manufacturers with inadequate standards. To increase profits, they may have scrimped, for example, on the quality of raw materials for the inactive ingredients, or on production or quality-assurance procedures.

Such situations have occasionally led to serious problems for patients taking the generic drugs; usually, however, the defects have been corrected before they could affect the health of consumers. Moreover, in the wake of such cases, FDA actions have resulted in the removal of a number of less-than-scrupulous generic-drug manufacturers from the marketplace.

It may well be that the bottom-line question is not "Are generic drugs appropriate substitutes for brand-name drugs?" but "Can a patient trust the substitution of a generic pharmaceutical product for a trademarked one?"

I submit that the best answer to this question is a variation of the old saw "Try it - you'll like it!"

If your physician, pharmacist or other health-care supplier wants to substitute a generic for the trademarked medication you've been taking for years, by all means try it. But be careful to report any changes in your health to your physician or pharmacist immediately - including changes in how you feel at different time of the day, in how you sleep and in signs you monitor regularly (blood pressure and blood-sugar levels, for example).

This may take work, as it entails your being well informed about your medical condition and being able to communicate with your health-care providers.

If your newly prescribed generic medication works as well as its brand-name counterpart, you may save some money. If it doesn't work as well, you can ask your provider to reinstate the original, trademarked product.