Drug interactions
When two or more drugs are given at the same time, they may exert their effects independently or they may interact. With the increase in the number of older patients who have retained some or all of their teeth and who may be on one or more long-term medications, identifying potential drug interactions that may occur between drugs prescribed in dental practice and the patient’s current medication is increasingly important.
Drug interactions can involve a variety of mechanisms, including those where the normal concentration of a drug in tissue fluid is either reduced or increased due to the effects of a second drug on its ADME (absorption, distribution, metabolism, excretion) properties or those where the pharmacological effects of the first drug are modified (reduced or enhanced) due to the pharmacological effects of the second drug. See Seymour21 and Dawoud et al.22 for more information on the principles of drug interactions in dentistry.
Not all drug interactions have serious consequences. However it is important that dentists are aware of potentially harmful interactions when prescribing.
The most frequent interactions and side effects observed with drugs commonly prescribed in dentistry are:
- interactions of non-steroidal anti-inflammatory drugs (NSAIDs), carbamazapine, azole antifungals and antibiotics with warfarin;
- incidence of myopathy after prescribing azoles and clarithromycin in those taking statins;
- asthma symptoms exacerbated following the use of NSAIDs.
Drug interactions can be minimised by ensuring that the patient’s medical history, including information on current medication, is up to date and by using alternative drugs where indicated.
The following tables list the most common potential drug interactions likely to be encountered when prescribing the drugs noted below. However, always consult Appendix 1 of the BNF1 or BNFC2 (available at www.medicinescomplete.com) for more comprehensive information on drug interactions.
Metronidazole
| Common interacting drug(s) | Recommendation |
|
Alcohol |
Advise patients taking metronidazole to avoid alcohol |
| Warfarin | Do not prescribe metronidazole for patients taking warfarin |
Macrolide antibiotics (e.g. clarithromycin)
| Common interacting drug(s) | Recommendation |
| Calcium channel blockers (e.g. nifedipine), carbamazepine, ciclosporin, domperidone, statins (e.g. simvastatin), theophylline, warfarin | Do not prescribe macrolide antibiotics for patients taking these drugs |
Azole antifungals (e.g. fluconazole, miconazole)
| Common interacting drug(s) | Recommendation |
| Statins, warfarin, theophylline | Do not prescribe azole antifungals for patients taking these drugs |
Non-steroidal anti-inflammatories (NSAIDs e.g. ibuprofen, diclofenac)
| Common interacting drug(s) | Recommendation |
|
Antihypertensive drugs especially beta-blockers (e.g. altenolol), ACE inhibitors (e.g. lisinopril) and diuretics |
Avoid prescribing NSAIDs or ensure course is for 5 days or less |
| Anticoagulants (e.g. warfarin, dabigatran) | Do not prescribe NSAIDs for patients taking these drugs |
| Aspirin | Do not prescribe NSAIDs taking a low daily dose of aspirin |
| Lithium | Do not prescribe NSAIDs |
| Methotrexate | Avoid prescribing NSAIDs |
| Selective serotonin reuptake inhibitors (SSRIs e.g. fluoxetine) | Avoid prescribing NSAIDs |
| Systemic corticosteroids | Only prescribe NSAIDs in combination with a proton-pump inhibitor |
Aspirin
| Common interacting drug(s) | Recommendation |
| Alcohol | Advise patients to avoid alcohol for 12 hours after taking aspirin |
| Clopidogrel | Avoid prescribing aspirin |
| Non-steroidal anti-inflammatories (NSAIDs e.g. ibuprofen, diclofenac) | Do not prescribe aspirin for patients taking these drugs |
| Selective serotonin reuptake inhibitors (SSRIs e.g. fluoxetine | Avoid prescribing aspirin |
| Systemic corticosteroids | Only prescribe aspirin in combination with a proton-pump inhibitor |
| Warfarin | Do not prescribe aspirin for patients taking warfarin |