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Dyspepsia - unidentified cause - Management
What issues should I consider before prescribing clarithromycin?
- Clarithromycin is generally well tolerated. It may cause gastrointestinal adverse effects (e.g. nausea, vomiting, diarrhoea) [ABPI Medicines Compendium, 2006].
- Drug interactions:
- Possible enhanced effect of aminophylline, theophylline, and carbamazepine (due to cytochrome P450 enzyme inhibition) [Aronson, 2006a]. Check levels if toxicity is suspected (e.g. palpitations, nausea, headache).
- Possible enhanced effect of warfarin: this is an established but unpredictable interaction. Monitor the international normalized ratio when both drugs are used (particularly in the elderly), and adjust the warfarin dose accordingly [Baxter, 2006]. There are reports of increased prothrombin times within three to five days after starting to take clarithromycin [Baxter, 2006].
- Possible QT interval prolongation: if possible, avoid giving erythromycin or clarithromycin if the person is already taking a drug that can potentially prolong the QT interval (e.g. antiarrhythmics, antipsychotics, tricyclic antidepressants) or if the person has hypokalaemia, which also increases the risk of QT prolongation [Baxter, 2006].
- Increased risk of myopathy in people taking atorvastatin or simvastatin (due to cytochrome P450 enzyme CYP3A4 inhibition) [CSM, 2004a].
- Contraceptives: antibiotics may cause the combined oral contraceptive pill or patch to fail during the first few weeks of treatment [Baxter, 2006] (see the CKS topic on Contraception for information on the combined oral contraceptive pill or patch).
- Advise women to use additional contraception during the course of treatment and for 7 days afterwards. If this 7-day period runs beyond the end of the pack of contraceptive pills, advise the woman to start a new pack without a break (omitting any inactive tablets) [FFPRHC, 2005; FFPRHC, 2007].
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