It should not be assumed that every generic drug product is as satisfactory as the trade-named product, though most generics are satisfactory. Bioavailability - the effective absorption of the drug product - varies between manufacturers and sometimes between different lots of a drug produced by the same manufacturer. In the case of a very small number of drugs, which usually have a low therapeutic index,poor solubility, or a high ratio of inert ingredients to active drug content, a specific manufacturer's product may give more consistent results. In the case of life-threatening diseases, the advantages of generic substitution are probably outweighed by the clinical urgency so that the prescription should be filled as written.
Source: Basic and Clinical Pharmacology, 8th ed. Bertram G. Katzung, ed. 2001 McGraw-Hill p. 1112 New York.
Related References:
"Generics - equal or not?" at http://www.australianprescriber.com/magazine/26/4/85/7/
"Quality use of generic medicines" at http://www.australianprescriber.com/magazine/27/4/80/1/
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DRUGS REQUIRING STRICT PRECAUTION IN PRESCRIBING, DISPENSING AND USE BECAUSE OF BIOAVAILABILITY PROBLEM AND AVAILABILITY IN PHILIPPINE MARKET IN SEVERAL BRANDS/MANUFACTURERS; PRESCRIPTION MUST BE FILLED ACCORDING TO THE SPECIFIED INTERNATIONAL NON-PROPRIETARY NAME (INN) AND BRAND NAME (B)
Total no. of drugs = 24
Core List = 16
Complementary List = 8
A. Core List
Atenolol
Carbamazepine
Dexamethasone
Diltiazem
Esmolol
Gliclazide
Haloperidol
Levothyroxine
Lithium Carbonate
Metformin
Metoprolol
Phenytoin
Propranolol
Rifampicin
Valproate disodium/Valproic Acid
Warfarin
B. Complementary List
Bromocriptine
Busulfan
Diltiazem
Felodipine
Gemfibrozil
Theophylline (anhydrous)
Valproate disodium/Valproic Acid
Verapamil
Source: Philippine National Drug Formulary Vol I 6th ed 2005 p. DOH Manila 2005 p. Appendix T p. 167
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