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).

• Amoxicillin is a broad spectrum antibiotic and is usually well tolerated, but nausea, vomiting, or diarrhoea can sometimes occur.
• It 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.
• Drug interactions:
• Contraceptives: broad spectrum antibiotics may cause combined hormonal contraceptives to fail during the first 3 weeks of antibiotic treatment (see the CKS topic on Contraception for information on the pill or the patch) [FFPRHC, 2004; FFPRHC, 2005; FFPRHC, 2007].
• Advise women 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.

• Common adverse effects include a metallic taste and gastrointestinal irritation (in particular nausea and vomiting). These are more common at higher doses.
• Advise that metronidazole should be taken with or after food.
• Drug interactions:
• Alcohol: some people taking oral metronidazole experience disulfiram-like reactions to alcohol (flushing, increased respiratory rate, increased pulse rate). Although there is no conclusive evidence to support an interaction between metronidazole and alcohol, people taking metronidazole should be advised of the possible consequences of drinking alcohol [Baxter, 2006].
• Anticoagulants: the anticoagulant effects of warfarin can be markedly increased by metronidazole [ABPI Medicines Compendium, 2008; Baxter, 2006].
• If concurrent use cannot be avoided, consider reducing the warfarin dosage appropriately (by between one-third to one-half) [Baxter, 2006].
• Warn the individual of the possible risk of increased bruising and bleeding. Advise when to seek medical help.
• Contraceptives: broad spectrum antibiotics may cause combined hormonal contraceptives to fail during the first 3 weeks of antibiotic treatment (see the CKS topic on Contraception for information on the pill or the patch) [FFPRHC, 2004; FFPRHC, 2005; FFPRHC, 2007].
• Advise women 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).

• Paracetamol is preferred because it can be given at all stages of pregnancy and during breastfeeding [Schaefer et al, 2007].
• Codeine may be used as an analgesic for pregnant women if paracetamol is not sufficiently effective. However, there is a potential to cause neonatal respiratory depression when used near to term [Schaefer et al, 2007].
• Although the amount of codeine excreted in breast milk is usually too small to be harmful, the British National Formulary warns that mothers vary considerably in their capacity to metabolize codeine, and fatal morphine toxicity has been reported in infants [BNF 54, 2007]. It has been recommended that codeine should only be used for short periods, and repeated dosages require close observation for somnolence [Schaefer et al, 2007].
• The nonsteroidal anti-inflammatory drug (NSAID), ibuprofen, can be considered for use during pregnancy (up to 27 weeks of gestation) and breastfeeding [Schaefer et al, 2007].
• Pregnancy
• Ibuprofen should not used beyond 27 weeks of gestation because this can lead to heart problems in the neonate (increased risk of constriction of the ductus arteriosus) [Schaefer et al, 2007].
• Breastfeeding
• Ibuprofen was not detected in breast milk following administration of 800–1600 mg daily in two small studies. No adverse effects on breastfed children were reported in both studies and also in a prospective study covering 21 mother-child pairs [Schaefer et al, 2007].