Friday, 4 October 2013

Drug Substitutions, Definitions

Pharmaceutical equivalents:
are drug products that have identical:
  • active drug ingredient (same salt, ester, or chemical form)
  • strength or concentration
  • dosage form
  • route of administration
but may differ in: color, shape, packaging, excipents, preservatives, expiration time, and labeling

Bioequivalent drug products:
are pharmaceutical equivalents that have similar bioavilability when given in the same dose and studied under similar experimental conditions

some drugs may be considered bioequivalent that are equal  in the extent of absorption but not in the rate of absorption

this is possible if the difference in the rate of absorption is considered clinically insignificant, for example, for drugs for chronic use.

two products are considered bioequivalent if the 90% CI of the relative mean Cmax, AUC(0-t) and AUC(0-∞) of the test (e.g. generic formulation) to reference (e.g. innovator brand formulation) should be within 80.00% to 125.00%

Generic substitution:
the process of dispensing a different drug product in place of prescribed drug product
the substituted drug product contains the same active ingredient or therapeutic moiety as the same salt or ester in the same dosage form but is made by a different manufacturer

Automatic Generic Substitution:
means that the pharmacist may dispense either the prescribed product, or they may replace it with a generic or another brand without being required to inform the patient or healthcare professional.

this can not be applied to NTI-drugs "narrow therapeutic index drugs" as patients might receive a generic medicine with effectively 25% more active ingredient than the branded medicine on one occasion and one with effectively 20% less active ingredient on the next, with NTI-drugs this may be lethal

Pharmaceutical alternative:
are drug products that contain same therapeutic moiety but as different salts, esters, or complexes. e.g. tetracycline phosphate or tetracycline HCl equivalent to 250mg tetracycline base are considered Pharmaceutical alternatives

different dosage forms and strengths within a product line by a single manufacturer are also considered Pharmaceutical alternatives. 

e.g. an extended-release dosage form and a standard immediate release dosage form of the same active ingredient. 
e.g. ampicillin suspension and ampicillin capsule

Therapeutic alternatives:
are drug products containing different active ingredients that are indicated for the same therapeutic or clinical objectives

active ingredients in the therapeutic alternatives are from the same pharmacological class and are expected to have the same therapeutic effect when administered to patients for such condition of use
for example, ibuprofen is given instead of aspirin; cimetidine may be given instead of ranitidine

Main Ref: Biopharmaceutics and pharmacokinetics, Dr.Hanan Refai, MUST, 2011  


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