When not to substitute

The Medicines Control Council (MCC) recommends that substitution should not occur when prescribing and dispensing medicines which:

a) Have a narrow therapeutic range;
b) Have been known to show erratic intra- and inter-patient responses;
c) Are contained in dosage forms that are likely to give rise to a clinically significant bioavailability problem, e.g. extended or delayed release preparations, as well as those known to be super bioavailable*;
d) Are intended for the critically ill and/or geriatric and paediatric patients.

In terms of the above-mentioned factors, the following medicines have, on occasion, been known to present bioequivalence problems and should ideally not be interchanged with a generic:

• Alendronate tablets or capsules
• Atenolol tablets or capules
• Carbamazepine tablets
• Chlorpromazine tablets
• Dexamethasone tablets
• Diethystilboestrol tablets
• Digoxin tablets
• Disulfiram tablets
• Ethinyl Oestradiol tablets
• Fluoxymesterone tablets
• Furosemide tablets
• Glibenclamide tablets
• Hydralazine, hydrochlorothiazide and Reserpine combination tablets
• Hydralazine & Hydrochlorothiazide combination tablets
• Hydrocortisone tablets
• Hydrocortisone Acetate injection
• Isoproterenol Metered dose inhaler
• Isoethrane Metered dose inhaler
• Isorbide Dinitrate sustained release tablets and capsules
• Itraconazole tablets or capsules
• Levodopa Capsules and tablets
• Nfedipine: all extended/delayed release formulations
• Oestrogens, Conjugated tablets
• Oestrogens Esterifies tablets
• Penicillin G Benzathine injections
• Phenytoin tablets and capsules
• Phytomenadion injection
• Prazosin Hydrochloride tablets 5mg*
• Prednisolone tablets
• Prednisolone Acetate injections
• Prednisolone Tebutate injection
• Prednisone tablets
• Promethazine tablets
• Propylthiouracil tablets
• Reserpine tablets
• Reserpine and Chlorothiazide combination tablets
• Reserpine & Trichloromethiazide combination tablets
• Tamoxifen tablets or capsules
• Theophylline controlled release tablets/capsules
• Triamcinolone tablets
• Trichloromethiazide tablets
• Warfarin Sodium tablets

Non-inclusion of any particular medicine does not necessarily mean it is substitutable. The list is periodically reviewed, and alterations are made at the discretion and recommendation of the MCC.

References:

• United States Food and Drug Administration. Generic drugs: what you need to know. [online] 2002 [cited 2007 Jul 09]. Available at: http://www.fda.gov/fdac/features/2002/502_generic.html
• United States Food and Drug Administration. Savings from generic drugs purchased at retail pharmacies. [online] 2004 [cited 2007 Jul 09]. Available at http://www.fda.gov/cder/consumerinfo/savingsfromgenericdrugs.htm
• United States Food and Drug Adminstration: Office of Generic Drugs. [online] 2007 [cited 2007 Jul 09]. Available at: http://www.fda.gov/cder/ogd/
• SA Medicines Control Council. Guidelines on generic substitution. Government Gazette 2003;25145:183-5.