These are drug products that contain the same active therapeutic moiety in different salt, ester, dosage forms and strength. For example penicillin G potassium salt and penicillin G sodium salt. Also, erythromycin estolate, erythromycin ethylsuccinate, and erythromycin stearate are considered pharmaceutical alternatives.

Products that contain the same active moiety but have different characteristics are considered pharmaceutical alternatives. For example sustained release theophylline tablets and immediate release theophylline tablets are pharmaceutical alternatives

These are drug products that contain the same active drug ingredients and are identical in strength, concentration, dosage form and route of administration.

Examples of pharmaceutical equivalents are aspirin tablets that contain 325 mg acetylsalicylic acid from different manufacturers, and different tablets containing 500 mg acetaminophen from different manufacturers

These are products of the same dosage form that contain the same active ingredient in the same amount. The active drug moiety reaches the systemic circulation at the same rate and to the same extent. The plasma concentration-time profile of the active moiety after administration of bioequivalent products are comparable and the difference is within an acceptable limits.

Usually the maximum plasma concentration and the time of the peak drug concentration are used to compare the rate of absorption, and the AUC is used to compare the extent of drug absorption.

Products that have the rate and extent of absorption of the active moiety within -20%/+20% are considered bioequivalents.

These are drug products that contain the same therapeutically active drug and have the same therapeutic effect and the same equal potential for adverse effects.

The ultimate criterion for assessing the equivalence of "equivalent" drug products would appear to be the therapeutic equivalency, the degree to which the products provide an effect which control a symptom or a disease. However, this is not easy to do, since many symptoms and disease processes are very difficult to quantitate e. g. anxiety, pain, bronchoconstriction, etc.

Since it is believed that the therapeutic effect of a drug is correlated with the drug blood level in vivo, assessing bioequivalence represents a reasonable alternative to assessing therapeutic equivalence.