Important aspects of prescribing information relevant to primary healthcare are covered in this section specifically for the drugs recommended in this CKS topic. For further information on contraindications, cautions, drug interactions, and adverse effects, see the electronic Medicines Compendium (eMC) (http://emc.medicines.org.uk), or the British National Formulary (BNF) (www.bnf.org).

• Paracetamol and ibuprofen are well tolerated when used for short periods [BNF 54, 2007]:
• Both paracetamol and ibuprofen are licensed for the relief of pain and fever from 3 months of age.
• As with other nonsteroidal anti-inflammatory drugs (NSAIDs), ibuprofen may worsen or precipitate gastrointestinal haemorrhage, asthma, hypertension, renal impairment, or cardiac failure. Avoid ibuprofen if there is a history of peptic ulcers. Paracetamol is often a safer option in older people.
• Paracetamol and ibuprofen rarely cause adverse effects when used in the short term [BNF 54, 2007]:
• Paracetamol has no notable adverse effects when used at the correct dosage.
• Ibuprofen may occasionally cause exacerbation of asthma and gastrointestinal adverse effects, such as discomfort, nausea, and diarrhoea.

• Phenoxymethylpenicillin (penicillin V) is a narrow-spectrum antibiotic and is usually well tolerated, but nausea, vomiting, or diarrhoea can sometimes occur.
• Phenoxymethylpenicillin should not be taken by people who have true penicillin allergy. However, gastrointestinal adverse effects alone (i.e. nausea, vomiting, or diarrhoea) do not constitute an allergy to penicillin [BNF 54, 2007].
• Drug interactions:
• Contraceptives: antibiotics may cause combined hormonal contraceptives (see the pill or the patch in the CKS topic on Contraception) to fail during the first 3 weeks of antibiotic treatment [FFPRHC, 2004; FFPRHC, 2005; FFPRHC, 2007].
• Advise the woman to use an additional method of contraception during the course of antibiotic treatment and for 7 days afterwards. If this 7-day period runs beyond the end of the pack of contraceptive pills or patch, advise the woman to start a new pack without a break (omitting any inactive tablets).
• Anticoagulants: documented reports of oral anticoagulant/penicillin (including amoxicillin) interaction are relatively rare [Baxter, 2006]. However, the British National Formulary advises that common experience in anticoagulant clinics is that the International Normalization Ratio (INR) can be altered by a course of broad-spectrum penicillin [BNF 54, 2007].
• Warn the individual of the possible risk of increased bruising and bleeding. Advise when to seek medical help.

• Erythromycin may cause gastrointestinal adverse effects (e.g. nausea, vomiting, diarrhoea) [BNF 54, 2007].
• Drug interactions:
• Contraceptives: antibiotics may cause combined hormonal contraceptives (see the pill or the patch in the CKS topic on Contraception) to fail during the first 3 weeks of antibiotic treatment [FFPRHC, 2004; FFPRHC, 2005; FFPRHC, 2007].
• Advise the woman to use an additional method of contraception during the course of antibiotic treatment and for 7 days afterwards. If this 7-day period runs beyond the end of the pack of contraceptive pills or patch, advise the woman to start a new pack without a break (omitting any inactive tablets).
• Drugs metabolized by cytochrome P450 isoenzymes (e.g. theophylline, carbamazepine, digoxin, warfarin) [Aronson, 2006]:
• The effects of these drugs may be increased because erythromycin can inhibit cytochrome P450 isoenzymes.
• Warfarin: experience in anticoagulant clinics suggests that the International Normalized Ratio (INR) may possibly be altered when warfarin is given with erythromycin [BNF 54, 2007]. Warn the individual of the possible risk of increased bruising and bleeding. Advise when to seek medical help.
• People taking drugs that can prolong the QT interval (e.g. antiarrhythmics, antipsychotics, tricyclic antidepressants), and people with hypokalaemia:
• Macrolides also prolong the QT interval, and therefore should, if possible, not be used together with these drugs.
• Macrolides should not be used in people with hypokalaemia, which also increases the risk of QT prolongation.
• People taking statins:
• The risk of myopathy and rhabdomyolysis is increased, as macrolides can inhibit the metabolism of statins [Aronson, 2006].
• Consider stopping simvastatin for the duration of erythromycin treatment [ABPI Medicines Compendium, 2009].
• For more information on drug interactions with macrolides, see the British National Formulary [BNF 54, 2007].

• Clarithromycin may cause gastrointestinal adverse effects (e.g. nausea, vomiting, diarrhoea), but this is less common than with erythromycin [BNF 55, 2008].
• Clarithromycin may cause the combined oral contraceptive pill or patch to fail during the first few weeks of treatment [Baxter, 2006]. 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].
• Advise people taking concomitant warfarin, statins, carbamazepine, theophylline, or aminophylline to seek advice if symptoms of toxicity to these drugs occur during treatment with clarithromycin.