BNF for Children 2011-2012

736 Appendix 1: Interactions BNFC 2011–2012Appendix 1: InteractionsTetracyclines (continued)Dairy Products: absorption of tetracyclines (exceptdoxycycline and minocycline) reduced by dairyproductsDiuretics: manufacturer of lymecycline advises avoidconcomitant use with diureticsErgot Alkaloids: increased risk of ergotism whentetracyclines given with ergotamine and methysergideIron: absorption of tetracyclines reduced by oral iron,also absorption of oral iron reduced by tetracyclinesLipid-regulating Drugs: absorption of tetracyclinepossibly reduced by colestipol and colestyramine. Retinoids: possible increased risk of benign intracranialhypertension when tetracyclines given with.retinoids (avoid concomitant use)Strontium Ranelate: absorption of tetracyclinesreduced by strontium ranelate (manufacturer ofstrontium ranelate advises avoid concomitant use)Ulcer-healing Drugs: absorption of tetracyclinesreduced by sucralfate and tripotassium dicitratobismuthateVaccines: antibacterials inactivate oral typhoidvaccine—see p. 620Zinc: absorption of tetracyclines reduced by zinc, alsoabsorption of zinc reduced by tetracyclinesTheophyllineAllopurinol: plasma concentration of theophyllinepossibly increased by allopurinolAnaesthetics, General: increased risk of convulsionswhen theophylline given with ketamine; increasedrisk of arrhythmias when theophylline given withhalothaneAnti-arrhythmics: theophylline antagonises anti-arrhythmiceffect of adenosine; plasma concentration oftheophylline increased by propafenone. Antibacterials: plasma concentration of theophyllinepossibly increased by azithromycin and isoniazid;metabolism of theophylline inhibited by.clarithromycin (increased plasma concentration);plasma concentration of theophylline increased by.erythromycin (also theophylline may reduceabsorption of oral erythromycin); plasma concentrationof theophylline increased by.ciprofloxacin and .norfloxacin; metabolism oftheophylline accelerated by rifampicin (reducedplasma concentration); possible increased risk ofconvulsions when theophylline given with.quinolones. Antidepressants: plasma concentration of theophyllineincreased by .fluvoxamine (concomitant use shouldusually be avoided, but where not possible halvetheophylline dose and monitor plasma-theophyllineconcentration); plasma concentration of theophyllinereduced by .St John’s wort—avoid concomitant use. Antiepileptics: metabolism of theophylline acceleratedby carbamazepine and .phenobarbital (reducedeffect); plasma concentration of both drugs reducedwhen theophylline given with .phenytoin. Antifungals: plasma concentration of theophyllinepossibly increased by .fluconazole and.ketoconazole. Antivirals: plasma concentration of theophylline possiblyincreased by aciclovir; metabolism of theophyllineaccelerated by .ritonavir (reduced plasmaconcentration)Anxiolytics and Hypnotics: theophylline possiblyreduces effects of benzodiazepines. Calcium-channel Blockers: plasma concentration oftheophylline possibly increased by .calcium-channelblockers (enhanced effect); plasma concentration oftheophylline increased by diltiazem; plasma concentrationof theophylline increased by .verapamil(enhanced effect)Corticosteroids: increased risk of hypokalaemia whentheophylline given with corticosteroidsCytotoxics: plasma concentration of theophylline possiblyincreased by methotrexateTheophylline (continued)Disulfiram: metabolism of theophylline inhibited bydisulfiram (increased risk of toxicity)Diuretics: increased risk of hypokalaemia when theophyllinegiven with acetazolamide, loop diuretics orthiazides and related diureticsDoxapram: increased CNS stimulation when theophyllinegiven with doxapram. Febuxostat: caution with theophylline advised bymanufacturer of .febuxostat. Interferons: metabolism of theophylline inhibited by.interferon alfa (consider reducing dose of theophylline)Leukotriene Receptor Antagonists: plasma concentrationof theophylline possibly increased by zafirlukast,also plasma concentration of zafirlukast reducedLithium: theophylline increases excretion of lithium(reduced plasma concentration)Oestrogens: plasma concentration of theophyllineincreased by oestrogens (consider reducing dose oftheophylline)Pentoxifylline: plasma concentration of theophyllineincreased by pentoxifyllineRoflumilast: avoidance of theophylline advised bymanufacturer of roflumilastSulfinpyrazone: plasma concentration of theophyllinereduced by sulfinpyrazoneSympathomimetics: manufacturer of theophyllineadvises avoid concomitant use with ephedrine inchildrenSympathomimetics, Beta 2 : increased risk of hypokalaemiawhen theophylline given with high doses ofbeta 2 sympathomimetics—see Hypokalaemia, p. 138. Ulcer-healing Drugs: metabolism of theophyllineinhibited by .cimetidine (increased plasma concentration);absorption of theophylline possibly reducedby sucralfate (give at least 2 hours apart)Vaccines: plasma concentration of theophylline possiblyincreased by influenza vaccineThiazolidinediones see AntidiabeticsThiopental see Anaesthetics, GeneralThiotepa. Antipsychotics: avoid concomitant use of cytotoxicswith .clozapine (increased risk of agranulocytosis)Muscle Relaxants: thiotepa enhances effects of suxamethoniumThioxanthenes see AntipsychoticsThyroid HormonesAntacids: absorption of levothyroxine possibly reducedby antacidsAnti-arrhythmics: for concomitant use of thyroidhormones and amiodarone see p. 83Antibacterials: metabolism of levothyroxine acceleratedby rifampicin (may increase requirements forlevothyroxine in hypothyroidism). Anticoagulants: thyroid hormones enhance anticoagulanteffect of .coumarins and .phenindioneAntidepressants: thyroid hormones enhance effects ofamitriptyline and imipramine; thyroid hormonespossibly enhance effects of tricyclicsAntiepileptics: metabolism of thyroid hormonesaccelerated by carbamazepine and phenobarbital(may increase requirements for thyroid hormones inhypothyroidism); metabolism of thyroid hormonesaccelerated by phenytoin (may increase requirementsin hypothyroidism), also plasma concentration ofphenytoin possibly increasedBeta-blockers: levothyroxine accelerates metabolismof propranololCalcium Salts: absorption of levothyroxine reduced bycalcium saltsCytotoxics: plasma concentration of levothyroxinepossibly reduced by imatinibIron: absorption of levothyroxine reduced by oral iron(give at least 2 hours apart)Lanthanum: absorption of levothyroxine reduced bylanthanum (give at least 2 hours apart)