Erythromycin Cimetidine

Sildenafil doses should be decreased when any potent cytochrome P450 3A4 inhibitor is used (e g., cimetidine, erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir, and saquinavir). Vardenafil doses vary accordingto which agent is used (2.5 mg q 72 h for ritonavir, 2.5 mg q 24 h for indinavir, ketoconazole 400 mg daily, and itraconazole 400 mg daily and 5 mg q 24 h for ketoconazole 200 mg daily, itraconazole200 mg daily, and erythromycin). Tadalafil doses are reduced only when it is used with the most potent cytochrome P450 3A4 inhibitors (e g., ketoconazole or ritonavir). 

Drugs that may affect antihistamines include aluminum/magnesium-containing acids, cimetidine, erythromycin, ketoconazole, MAO inhibitors, and rifamycins (eg, rifampin). Drugs that may be affected by antihistamines include alcohol and CNS depressants, beta-blockers, MAO inhibitors, metyrapone, nefazodone, selective serotonin reuptake inhibitors (SSRIs), and venlafaxine. 

Drugs that may affect valproic acid include carbamazepine, charcoal, chlorpromazine, cholestyramine, cimetidine, erythromycin, ethosuximide, felbamate, lamotrigine, phenytoin, rifampin, and salicylates. Drugs that may be affected by valproic acid include carbamazepine, clonazepam, diazepam, ethosuximide, lamotrigine, phenobarbital, phenytoin, tolbutamide, tricyclic antidepressants, warfarin, and zidovudine. 

Cimetidine, erythromycin, and dextropropoxyphene had no effect on the pharmacokinetics of MHD. Results with warfarin show no evidence of interaction with either single or repeated doses of oxcarbazepine. 

Uses Obesity Action Blocks uptake of norepinephrine, serotonin, dopamine Dose 10 mg/d PO, may to 5 mg after 4 wk Caution [C, -] w/ SSRIs, Li, dextromethorphan, opioids Contra MAOI w/in 14 d, uncontrolled HTN, arrhythmias Disp Caps SE HA, insomnia, xerostomia, constipation, rhinitis, tach, HTN Interactions T Risk of serotonin synd W/ dextromethorphan, ergots, fentanyl, Li, meperidine, MAOIs, naratriptan, pentazocine, rizatriptan, sumatriptan, SSRIs, tryptophan, zolmitriptan, St. John s wort effects W/ cimetidine, erythromycin, ketoconazole T CNS depression W/ EtOH EMS Use fentanyl w/ caution, may T risk of serotonin synd concurrent EtOH use can T CNS depression OD May cause tach, HTN, diaphoresis, HA, fever, agitation, muscle tremors, and Szs symptomatic and supportive... 

Theophylline Cimetidine, erythromycin, influenza vaccine, oral contraceptives Potentiation. 

Plasma levels of valproate may also be Increased by felbamate, chlorpromazine, fluoxetine, fluvoxamine, topiramate, cimetidine, erythromycin, and ibuprofen... 

Recommendations have been presented for correction of theophylline doses dnring concomitant medication with some of the above dmgs (SEDA-8, 130) (45). Concomitant therapy with aUopnrinol, cimetidine, erythromycin, furosemide, isoprenahne, or propranolol requires a reduction in dose of abont 20-30% for oleandomycin the reduction shonld be abont 50%. 

Clinically important, potentially hazardous interactions with alcohol, cimetidine, erythromycin, imipramine, ketoconazole, promethazine, rifampicin, rifampin, thioridazine... 

Increased effects with chlorpromazine, cimetidine, erythromycin, felbamate, salicylates... 

Neonates require close monitoring if their mothers received enzyme inducers such as phenytoin, phenobar-bital, carbamazepine, or rifampin during pregnancy or if they need one of these drugs themselves. Examples of drugs that inhibit the metabolism of other medications include cimetidine, erythromycin, and ketoconazole." ... 

CYP3A4 alprazolam, calcium channel blockers, cisapride, clarithromycin, cyclosporin A, erythromycin, HIV protease inhibitors, lidocaine, midazolam, simvastatin, terfenadine carbamazepine, dexamethsone, phenobarbital, phenytoin, rifampicin, St John s wort cimetidine, erythromycin, grapefruit juice, HIV protease inhibitors, itraconazole, ketoconazole... 

Warfarin Cimetidine, erythromycin, lovaslatin, metronidazole Increased anticoagulant effect via inhibition of warfarin metabolism... 

Especially the inhibition or induction of cytochrome P450 subtype 3A4 (CYP 3A4) is clinically relevant, because a variety of active substances and food substances (e.g. grapefruit juice) are able to affect this enzyme. Substances inhibiting CYP 3A4 include ciclosporin, dihydropyridines, verapamil, midazolam, paclitaxel, simvastatin, lovastatin, atorvastatin, cimetidine, erythromycin, troleandomycin, ketoconazole (and other azoles). Substances inducing CYP 3A4 include steroids, rifampicin, phenobarbital and St John s wort. 

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