Therapeutic Handbook - GGC Prescribing

Antibiotic Allergy and InteractionsAllergy• Specifically enquire as to the nature of “allergy”. Abdominal pain, nausea, vomiting or dyspepsiadoes not constitute allergy.• Document both the allergy and the nature of the allergy in the patient’s medical notes and on thedrug kardex.• Do not give penicillin, cephalosporin or other beta-lactam* antibiotic if patient has a history ofanaphylaxis, urticaria, or rash immediately after penicillin administration.• Adults with a history of a minor rash (e.g. non-confluent, non-pruritic rash restricted to a smallarea of the body), or a rash that occurs > 3 days after starting an antibiotic course are unlikelyto have an antibiotic allergy and therefore the antibiotic should not be withheld unnecessarily forserious infections.• Penicillin allergy occurs in 1-10% of patients. Anaphylaxis occurs in < 0.05% of treated patients.• Co-trimoxazole: rash occurs in > 1 in 100 patients prescribed co-trimoxazole. If a rash occursdiscontinue co-trimoxazole immediately.• Be aware of the components of antibiotic co-formulations e.g. co-trimoxazole (trimethoprim andsulphamethoxazole), co-amoxiclav (amoxicillin and clavulanic acid).• For further advice on antibiotic allergy please contact the allergy service – see Appendix 6 forcontact detail.*Beta-lactam antibiotics include: amoxicillin; ampicillin; benzylpenicillin (Penicillin G); co-amoxiclav(Augmentin ® ); flucloxacillin; phenoxymethylpenicillin (Penicillin V); piperacillin / tazobactam(Tazocin ® ), cefaclor; cefalexin; cefotaxime; ceftazidime; ceftriaxone; cefuroxime; aztreonam;meropenem; imipenem with cilastatin, doripenem, ertapenem (see BNF for more details).InfectionsImportant Antibiotic Drug InteractionsThis is not a comprehensive list; for further information refer to a pharmacist or Appendix 1 of the BNF.Clarithromycin: numerous interactions (some potentially life-threatening) via;i) Enzyme inhibition e.g. carbamazepine and simvastatin (see BNF Appendix 1).ii) QT prolongation e.g. citalopram, fluconazole; seek advice from pharmacy. Consider othermedical risk factors for QT prolongation. Also see page 7 (Assessing Medicines on Admissionin Acute Patients) and Postscript Extra article on drug induced QT prolongation atwww.ggcprescribing.scot.nhs.uk.Rifampicin: numerous interactions through enzyme induction (see BNF Appendix 1).Statins: Avoid concomitant use with macrolides and sodium fusidate (consult BNF for details).Consider using an alternative antibiotic class; liaise with microbiology / infectious diseases unit whereappropriate.Warfarin: INR may be altered by many antibiotics, particularly if a course is prolonged (check BNFAppendix 1).Oral contraceptive pill: no additional contraceptive precautions are now required when combinedoral contraceptives are used with antibiotics which do not induce liver enzymes, unless diarrhoea orvomiting occur (see BNF for advice).Page 204