E-drug: Fexofenadine to replace terfenadine (cont'd)
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Further to the discussion:
How about replacing all of the non-sedating agents with "properly"
dosed chlorpheniramine - here is the rational in no particular order
(see Can Med Assoc J 1997;157:37-8)
1) It is my understanding that, in general all antihistamines are pretty
much equally effective - however, I have seen one comparison of
brompheniramine (similar to chlorpheniramine) to terfenadine and
brompheniramine appeared to be more effective in allergic rhinitis
but also caused more sedation (Ann Allergy Asthma Immunol
1996;77:365-70) - the dose of brompheniramine used was in my
opinion much too large (12 mg BID - see below) so maybe the
patients were too drowsy and just thought that their symptoms
were less!!
2) The dosage recommendation for chlorpheniramine found on the box
and in various textbooks (4 mg every 4-6 hours) is completely
wrong and one of the main reasons patients often cannot tolerate
the drug - chlorpheniramine has a 17 hour half life which makes it
one of the longest acting antihistamines and really is a once-a-day
antihistamine - anyone know why there is a sustained release
chlorpheniramine available? - probably more of a marketing gimmick
than a therapeutic advantage
3) I, and a number of my colleagues, have found that a single 4 mg
(non-sustained release) given at bedtime is often very effective for
a lot of patients - if not, we bump the dose up to 8 mg - if 4 mg
is effective but causes excessive sedation (rarely) it goes away in
few days as the patient builds up tolerance and if not, we back off
the dose to 2 mg at bedtime - if 8 mg is not effective we try
something else
4) I am not aware of chlorpheniramine causing cardiac problems like
that seen with some of the newer antihistamines
5) In Canada, generic chlorpheniramine costs 3 dollars for a thousand
(1000) 4 mg tablets
Any evidence or personal experience that supports or refutes these
comments would be much appreciated. Thanks.
James McCormack, Pharm.D.
Associate Professor
Faculty of Pharmaceutical Sciences
c/o Pharmacy Department
St. Paul's Hospital
1081 Burrard St., Vancouver, B.C., Canada, V6Z 1Y6
Tel: 604-631-5150 Fax: 604-631-5154
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