Workshop 4: Drug Interactions



Workshop 4.2: Drug Interactions

|Case Scenario 1 |

|Question |Is it okay to take amoxicillin whilst taking the pill? |

| | |

|What further background |PERSON |MEDICINES |

|information do you need to | | |

|clarify the question and | | |

|minimise the risks when | | |

|advising the caller? | | |

| |Who is asking? |Medicines (name,dose,freq)? |

| |28 year old female - about herself |Amoxicillin 500mg three times a day. |

| | |Cilest. |

| |New or worsening symptoms? |How many pills left? 12 |

| |GP diagnosed a chest infection this morning. |Have you taken the antibiotic? No |

| | | |

| |Any allergies/medical conditions? |Why asking about medicines? |

| |No allergies. |Forgot to check that doctor aware I was taking the pill.|

| | | |

| | | |

|Gather the further background information BEFORE searching for information. |

|What information sources |eBNF: |

|would you use? |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 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? |There is a risk that amoxicillin may stop the pill from working properly. |

| | |

|Or would you refer? |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. |

Workshop 4.2: Drug Interactions

|Case Scenario 2 |

|Question |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? |

|What further background |PERSON |MEDICINES |

|information do you need to | | |

|clarify the question and | | |

|minimise the risks when | | |

|advising the caller? | | |

| |Who is asking? |Medicines (name,dose,freq)? |

| |61-year old female - about herself. |Warfarin 3mg once a day. |

| | |Ciprofloxacin 500mg twice a day for 1 week. |

| |New or worsening symptoms? | |

| |Doctor has diagnosed a urinary tract infection. |Why asking about medicines? |

| | |Yellow dosing book warns about taking other medicines |

| |Any allergies or medical conditions? |with warfarin. |

| |No allergies. DVT 3 months ago. | |

|Gather the further background information BEFORE searching for information. |

|What information sources |eBNF: |

|would you use? |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. |

|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. |

Workshop 4.2: Drug Interactions

|Case Scenario 3 |

|Question |Is it OK to take Nurofen® with my yellow tablets? |

|What further background |PERSON |MEDICINES |

|information do you need to | | |

|clarify the question and | | |

|minimise the risks when | | |

|advising the caller? | | |

| | | |

| |Who is asking? |Medicines (name, dose, freq)? |

| |50 yr old man about himself. |Methotrexate 7.5mg weekly as 3 x 2.5mg tablets |

| | |Nurofen® Liquid Capsules |

| |New or worsening symptoms? | |

| |Have a really bad sore throat. |Why taking? |

| | |Have had Rheumatoid Arthritis for past 5 years. |

| |Any allergies or medical conditions? | |

| |No allergies. | |

|Gather the further background information BEFORE searching for information. |

|What information sources |MedicinesChest: |

|would you use? |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 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? |Patients taking Methotrexate should only be taken ibuprofen under the supervision of their doctor. |

|Or would you refer? | |

| |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. |

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