This
page is from a campaign
by award-winning investigative journalist Brian Deer in The
Sunday Times of London over
risks and side-effects
from this antibiotic, marketed
under many names, such as Bactrim,
Bactrim DS, Septra, Septra DS,
Septrin, Sulfatrim, SMZ/TMP,
Septran and co-trimoxazole | The investigation | Symptom searcher | Tell Brian & help others
Trimethoprim is one of the two key
ingredients in this drug - although
regarded as less problematic than the
other component sulfamethoxazole. Below is
information on trimethoprim side-effects
given by Martindale, the authoritative
reference work from the Pharmaceutical
Society of Great Britain (33rd edition,
April 2002). You can read personal
stories in letters to The Sunday
Times and in emails to this website
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Trimethoprim
(as in Bactrim, Septra, Septrin
etc) Adverse
effects and treatment
Trimethoprim
is reasonably well tolerated in
general, and the most frequent
adverse effects at usual doses
are pruritis and skin rash (in
about 3 to 7% of patients) and
mild gastrointestinal
disturbances including nausea,
vomiting, and sore mouth.
Rarely, more severe
effects have been reported.
Sulfonamide-like skin reactions,
including exfoliative dermatitis,
erythema multiforme,
Stevens-Johnson syndrome, and
toxic epidermal necrolysis have
occurred. Disturbances of liver
enzyme values and cholestatic
jaundice have been associated
with trimethoprim. Rises in serum
creatinine and blood-urea
nitrogen have been reported
although it is unclear whether
this represents genuine renal
dysfunction or inhibition of
tubular secretion of creatinine.
Photosensitivity has been
reported. Fever is not
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uncommon but occasionally
hypersensitivity reactions may be severe
and manifest as anaphylaxis. Cases of
aseptic meningitis have also been
reported.
Trimethoprim may
cause a depression of haematopoiesis due
to interference of the drug in the
metabolism of folic acid, particularly
when given over a prolonged period or in
high doses. This may manifest as
megaloblastic anaemia, or as
thrombocytopenia and leucopenia;
methaemoglobinaemia has also been seen.
Calcium folinate 5 to 15mg daily by mouth
may be given to counter this effect. Trimethoprim
is teratogenic in animals.
Hyperkalaemia. Trimethoprim
has been reported to induce hyperkalaemia
, particularly in HIV-infected patients
being treated for Pneumocystis carinii
pneumonia or in the elderly. The
hyperkalaemia may be due to
amiloride-like potassium-sparing
properties of trimethoprim, and
may be potentiated by ACE inhibitors.
Precautions
Trimethoprim should
not be given to patients with a history
of hypersensitivity to the drug, and it
should be discontinued if a skin rash
appears. Care is necessary in
administering trimethoprim to
patients with impaired renal function to
avoid accumulation and toxicity: it
should not be given in severe renal
impairment unless blood concentrations
can be monitored. It should be used with
caution in patients with severe hepatic
damage as changes may occur in the
absorption and metabolism of trimethoprim.
It is suggested that regular
haematological examination should be made
during prolonged courses of treatment;
trimethoprim should not usually be
given to patients with serious
haematological disorders and particularly
not in megaloblastic anaemia secondary to
folate depletion. Caution should be taken
in patients with actual, or possible,
folate deficiency and administration of
folinic acid should be considered. Trimethoprim
should be avoided during pregnancy.
Trimethoprim appears in breast milt
and care is required when it is used in
breast-feeding mothers. Elderly patients
may be more susceptible to adverse
effects and a lower dosage may be
advisable.
Trimethoprim may
interfere with some diagnostic tests,
including serum-methotrexate assay where
dihydrofolate reductase is used and the
Jaffe reaction for creatinine.
Pharmaceutical
Society of Great Britain, April 2002.
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