Workshop 4.2: Drug Interactions
Case Scenario 1
Question
What further
background
information do
you need to
clarify the
question and
minimise the risks
when advising the
caller?
Is it okay to take amoxicillin whilst taking the pill?
PERSON
MEDICINES
Who is asking?
28 year old female - about herself
Medicines (name,dose,freq)?
Amoxicillin 500mg three times a day.
Cilest.
New or worsening symptoms?
How many pills left? 12
GP diagnosed a chest infection this Have you taken the antibiotic? No
morning.
Why asking about medicines?
Any allergies/medical conditions? Forgot to check that doctor aware I
No allergies.
was taking the pill.
Gather the further background information BEFORE searching for information.
What information
sources would
you use?
eBNF:
Some antibacterials that do not induce liver enzymes (e.g. ampicillin,
doxycycline) may reduce the efficacy of combined oral contraceptives by
impairing the bacterial flora responsible for recycling ethinylestradiol from
the large bowel. Additional contraceptive precautions should be taken whilst
taking a short course of an antibacterial drug that is not enzyme-inducing
and for 7 days after stopping. If these 7 days run beyond the end of a packet
the next packet should be started immediately without a break (in the case
of ED tablets the inactive ones should be omitted). If the antibacterial course
exceeds 3 weeks, the bacterial flora develop antibacterial resistance and
additional precautions become unnecessary unless a new antibacterial is
prescribed; additional precautions are also unnecessary if a woman starting
a combined oral contraceptive has been on a course of antibacterial therapy
for 3 weeks or more.
eMC / Cilest:
Irregular cycles and reduced reliability of oral contraceptives may occur
when these preparations are used concomitantly with drugs such as
anticonvulsants, barbiturates, antibiotics, (eg tetracyclines, ampicillin,
rifampicin, etc), griseofulvin, activated charcoal and certain laxatives.
NetDoctor / Cilest:
Other antibiotics do not affect the breakdown of the pill by the liver.
However, if you are prescribed another antibiotic medicine (eg amoxicillin,
doxycycline) while taking this contraceptive, there is a very low risk that the
antibiotic may make your pill less effective at preventing pregnancy.
Although the risk of this is very low, the personal and ethical consequences
of an unwanted pregnancy can be very serious. For this reason, it is
recommended that you use an extra method of contraception (eg condoms)
while you are taking the antibiotic and for seven days after finishing the
course. If these seven days run beyond the end of a pill packet, a new
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0
packet should be started without a break. For more information talk to your
pharmacist.
If you are prescribed an antibiotic for longer than three weeks, eg for
treating acne, then you don't need to use extra contraception after you have
been taking that antibiotic for three weeks or longer. But, if you are then also
prescribed a short course of a different antibiotic, you will need to use extra
contraception again, as above. For more information talk to your pharmacist.
Medicines Complete - Stockley:
The oral contraceptive / penicillin interaction is inadequately established and
controversial. The total number of failures is extremely small. However, the
personal and ethical consequences of an unwanted pregnancy can be very
serious. For this reason the general advice is that a second (barrier) method
of contraception be used whilst taking the penicillin and for 7 days after
finishing the course. The FPA recommend that if the 7 days run beyond the
end of the packet then the new packet should be started without a pill-free
break.
What advice
would you give?
Or would you
refer?
There is a risk that amoxicillin may stop the pill from working properly.
Advise to use a barrier method during the time that she is on the antibiotic
and for 7 days following the end of the course (i.e. 14 days).
As there are only 12 tablets left in the pack, start the next pack of pills
straight away without the 7-day pill free period. Explain that this is safe and
that she will not get the usual withdrawal bleed.
Further learning points
For questions about the contraceptive pill
 Ask how many pills are left in the pack
 Ask if the second medicine has already been taken. May need to assess the risk of
contraceptive failure.
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0
Workshop 4.2: Drug Interactions
Case Scenario 2
Question
What further
background
information do
you need to
clarify the
question and
minimise the risks
when advising the
caller?
I have just been to see my doctor. He has given me some ciprofloxacin. I
am taking warfarin. Is it ok to take them together?
PERSON
MEDICINES
Who is asking?
61-year old female - about herself.
Medicines (name,dose,freq)?
Warfarin 3mg once a day.
Ciprofloxacin 500mg twice a day for
1 week.
New or worsening symptoms?
Doctor has diagnosed a urinary tract
Why asking about medicines?
infection.
Yellow dosing book warns about
Any
allergies
or
medical taking other medicines with warfarin.
conditions?
No allergies. DVT 3 months ago.
Gather the further background information BEFORE searching for information.
What information
sources would
you use?
eBNF:
ciprofloxacin + coumarins - potentially hazardous
ciprofloxacin enhances anticoagulant effect of coumarins
Change in patient's clinical condition, particularly associated with liver
disease, intercurrent illness, or drug administration, necessitates more
frequent testing. Major changes in diet (especially involving salads and
vegetables) and in alcohol consumption may also affect anticoagulant
control
eMC- SPC / Ciproxin®:
Prolongation of bleeding time has been reported during concomitant
administration of ciprofloxacin and oral anti-coagulants.
eMC- PIL / Ciproxin®:
Remind your doctor if you are taking drugs that thin the blood
(anticoagulants) such as warfarin
NetDoctor
Ciprofloxacin may enhance the anti-blood-clotting effect of anticoagulant
medicines such as warfarin. As this may increase the risk of bleeding, your
blood clotting time (INR) should be monitored more frequently if you are
taking ciprofloxacin with an anticoagulant.
What advice
would you give?
Ciprofloxacin can in some people enhance the effects of warfarin. This
means it can make your blood too thin and increase the risk of bleeding.
Or would you
refer?
Suggest you phone your GP. He may want to change your antibiotic or
monitor your blood more closely.
Signs that your blood is too thin include nosebleeds, easily bruising and
blood in the urine. If these occur, speak to your GP immediately.
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0
Further learning points
Warfarin is a narrow therapeutic range drug
 small increases in blood level can lead to haemorrhage including stroke
 small decreases in blood level can result in blood clots (stroke, DVT, PE)
Ciprofloxacin inhibits the metabolism of many medicines.
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0
Workshop 4.2: Drug Interactions
Case Scenario 3
Question
What further
background
information do
you need to
clarify the
question and
minimise the
risks when
advising the
caller?
Is it OK to take Nurofen® with my yellow tablets?
PERSON
MEDICINES
Who is asking?
50 yr old man about himself.
Medicines (name, dose, freq)?
Methotrexate 7.5mg weekly as 3 x
2.5mg tablets
Nurofen® Liquid Capsules
New or worsening symptoms?
Have a really bad sore throat.
Any
allergies
conditions?
No allergies.
or
Why taking?
medical Have had Rheumatoid Arthritis for
past 5 years.
Gather the further background information BEFORE searching for information.
What information
sources would
you use?
MedicinesChest:
Nurofen® Liquid Capsules soft capsule containing:
Ibuprofen 200 mg
eBNF:
methotrexate + ibuprofen potentially hazardous
Excretion of methotrexate reduced by ibuprofen (increased risk of toxicity)—
but for concomitant use in rheumatic disease see Methotrexate, section
10.1.3
Aspirin and other NSAIDs If aspirin or other NSAIDs are given concurrently
the dose of methotrexate should be carefully monitored. Patients should be
advised to avoid self-medication with over-the-counter aspirin or ibuprofen.
Important
The dose for methotrexate is a weekly dose. To avoid error with low-dose
methotrexate, it is recommended that:
 the patient is carefully advised of the dose and frequency and the
reason for taking methotrexate and any other prescribed medicine
(e.g. folic acid);
 only one strength of methotrexate tablet (usually 2.5 mg) is
prescribed and dispensed.
 the prescription and the dispensing label clearly show the dose and
frequency of methotrexate administration;
 the patient is warned to report immediately the onset of any feature
of blood disorders (e.g. sore throat, bruising, and mouth ulcers),
liver toxicity (e.g. nausea, vomiting, abdominal discomfort, and dark
urine), and respiratory effects (e.g. shortness of breath).
eMC - SPC: Maxtrex®
Interaction with other medicinal products and other forms of interaction
Methotrexate dosage should be monitored if concomitant treatment with
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0
NSAIDs is commenced, as concomitant use of NSAIDs has been associated
with fatal methotrexate toxicity.
Patients should report all symptoms and signs suggestive of infection,
especially sore throat.
eMC – PIL: Maxtrex®
Check with your doctor before taking any other medications including any
you have bought without a prescription in particular: NSAIDs (non-steroidal
anti-inflammatory drugs) e.g. ibuprofen, indometacin or aspirin (for pain
relief or inflammation), antibiotics (chloramphenicol, penicillin,
sulphonamides, co-trimoxazole, trimethoprim and tetracyclines), thiazides (a
group of diuretics for fluid retention), hypoglycaemics (for lowering blood
sugar levels), p-aminobenzoic acid, acritretin (treatment for psoriasis or skin
disorders), diphenylhydantoins (for epilepsy), probenicid, sulphinapyrazone
(used to treat gout), phenytoin (an antiepileptic), including vitamin
preparations containing folic acid or its derivatives, and non-prescription
remedies, or receiving the anaesthetic gas nitrous oxide.
Methotrexate can make you more likely to catch infections. If you think you
have an infection, a sore throat, fever, chills, or achiness during treatment
you should tell your doctor immediately.
NetDoctor:
Salicylate medicines such as aspirin, and non-steroidal anti-inflammatory
drugs (NSAIDs) such as ibuprofen, ketoprofen and diclofenac can reduce
the removal of methotrexate from the body. This can cause levels of
methotrexate can build up in the blood, increasing the risk of side effects.
For this reason, people taking methotrexate should avoid buying aspirin or
NSAIDs such as ibuprofen to take as painkillers or anti-inflammatories.
These medicines should only be used on the advice of the doctor who is
monitoring your methotrexate treatment, so that changes can be made to
your methotrexate dose if necessary.
This medicine may rarely cause a decrease in the normal amounts of blood
cells in the blood. For this reason you should consult your doctor
immediately if you experience any of the following symptoms: unexplained
bruising or bleeding, purple spots, sore throat, mouth ulcers, high
temperature (fever), feeling tired or general illness. Your doctor may want to
take a blood test to check your blood cells.
What advice
would you give?
Or would you
refer?
Patients taking Methotrexate should only be taken ibuprofen under the
supervision of their doctor.
Sore throat symptoms may be a sign of a serious blood disorder. The
patient should see the doctor as soon as possible for tests.
Further learning points
Methotrexate is a type of medicine called a cytotoxic antimetabolite. Methotrexate is used to
treat three different conditions: rheumatoid arthritis, psoriasis and cancer of various types.
Treatment with methotrexate is usually only initiated by hospital specialists, and regular blood
tests are needed to monitor for potential side effects.
Role Preparation for NHS Direct NAs: Handling Medicines Calls
November 2007 v1.0