Clinical Pharmacology and Therapeutics

PRESCRIBING IN PREGRANCY 51
Case history
A 20-year-old female medical student attended her GP
requesting a course of Septrin® (co-trimoxazole) for cystitis.
She tells her GP that her last menstrual bleed was about
six weeks earlier. She did not think she was at risk of pregnancy
as her periods had been irregular since stopping the
oral contraceptive one year previously due to fears about
thrombosis, and her boyfriend used a condom. Physical examination,
which did not include a vaginal examination, was
normal. Urinalysis was 1 positive for blood and a trace of
protein.
Question
Why should the GP not prescribe co-trimoxazole for this
patient?
Answer
Until proven otherwise, it should be assumed that this
woman is pregnant. Co-trimoxazole (a combination of sulfamethoxazole
and trimethoprim) has been superseded by
trimethoprim alone as a useful drug in lower urinary tract
infection (UTI). The sulfamethoxazole does not add significant
antibacterial advantage in lower UTI, but does have
sulphonamide-associated side effects, including the rare
but life-threatening Stevens–Johnson syndrome. Both sulfamethoxazole
and trimethoprim inhibit folate synthesis
and are theoretical teratogens. If pregnancy is confirmed
(urinary frequency is an early symptom of pregnancy in
some women, due to a progesterone effect) and if the
patient has a lower UTI confirmed by pyuria and bacteria
on microscopy whilst awaiting culture and sensitivity results,
amoxicillin is the treatment of choice. Alternatives include
an oral cephalosporin or nitrofurantoin. Note that lower
urinary tract infection in pregnancy can rapidly progress to
acute pyelonephritis.
FURTHER READING
Anon. Antiepileptics, pregnancy and the child. Drugs and Therapeutics
Bulletin 2005; 43 no 2.
Koren G. Medication, safety in pregnancy and breastfeeding: the evidencebased
A–Z clinicians pocket guide. Maidenhead: McGraw-Hill, 2006.
Rubin PC. Prescribing in pregnancy, 3rd edn. London: Blackwell, BMJ
Books, 2000.
McElhatton PR. General principles of drug use in pregnancy.
Pharmaceutical Journal 2003; 270: 305–7.
FURTHER INFORMATION FOR HEALTH
PROFESSIONALS
National Teratology Information Service
Regional Drug and Therapeutics Centre
Wolfson Unit
Clarement Place
Newcastle upon Tyne
NE1 4LP
Tel. 0191 232 1525