Rifampin phenytoin and

Itraconazole has significant interactions with a number of commonly prescribed drugs, such as rifampin, phenytoin, and carbamazepine. Itraconazole raises serum digoxin and cyclosporine levels and may affect the metabolism of oral hypoglycemic agents and coumadin. Absorption of itraconazole is impaired by antacids, Hj blockers, proton pump inhibitors, and drugs that contain buffers, such as the antiretroviral agent didanosine. 

Tucker RM, Denning DW, Hanson LH, et al. Interaction of azoles with rifampin, phenytoin, and carbamazepine in vitro and clinical observations. Clin Infect Dis 1992 14 165-174. 

Phenytoin interacts widi many different drugp. For example isoniazid, chloramphenicol, sulfonamides, benzodiazepines, succinimides, and cimetidine all increase phenytoin blood levels. The barbiturates, rifampin, theophylline, and warfarin decrease phenytoin blood levels. When administering the hydantoins with meperidine, die analgesic effect of meperidine is decreased. 

Oral azoles are associated with significant interactions, particularly due to cytochrome P-450 isoenzymes. Medications that interact with azoles include warfarin, phenytoin, theophylline, rifampin, cyclosporine, and zidovudine. For patients receiving only a few doses, these interactions do not pose a significant risk. These interactions may pose a risk for patients receiving long-term suppressive therapy for recurrent infections. 

Cholestyramine, calcium carbonate, sucralfate, aluminum hydroxide, ferrous sulfate, soybean formula, and dietary fiber supplements may impair the absorption of levothyroxine from the GI tract. Drugs that increase nondeiodinative T4 clearance include rifampin, carbamazepine, and possibly phenytoin. Amiodarone may block the conversion of T4 to T3. 

Commonly used drugs that induce liver enzymes (rifampin, phenytoin, carbamazepine, barbiturates, primidone, topiramate) and reduce efficacy of CHC... 

Buspirone (BuSpar) [Anxiolytic] WARNING Closely monitor for worsening depression or emergence of suicidality Uses Short-term relief of anxiety Action Antianxiety antagonizes CNS serotonin receptors Dose Initial 7.5 mg PO bid T by 5 mg q2-3d to effect usual 20-30 mg/d max 60 mg/d Contra w/ MAOI Caution [B, /-] Avoid w/ severe hepatic/renal insuff Disp Tabs SE Drowsiness, dizziness, HA, N, EPS, serotonin synd, hostility, depression Notes No abuse potential or physical/psychologic d endence Interactions T Effects W/ erythromycin, clarithromycin, itraconazole, ketoconazole, diltiazem, verapamil, grapefruit juice effects W/ carbamazepine, rifampin, phenytoin, dexamethasone, phenobarbital, fluoxetine EMS T Sedation w/ concurrent EtOH use grapefruit juice may T risk of adverse effects OD May cause dizziness, miosis, N/V symptomatic and supportive... 

Enzyme inducers [P] Barbiturates, phenytoin, and rifampin may enhance 13 -blocker metabolism other enzyme inducers may produce similar effects. 

There are many drugs that increase the rate of the liver s metabolism. More commonly used medications that fall into this category include rifampin, which is used to treat tuberculosis, and dilantin, phenytoin, and carbamazepine, which are medications commonly used to treat seizures and epilepsy. Chronic alcohol abuse also speeds up the metabolism of the liver. Since all of these substances cause the liver to break down methadone faster then it normally would, one way to correct the problem would be to increase the dose of methadone or break down the dose into several smaller doses given throughout the day. This should only be done on a physician s advice. 

UGT1A6 is a high-affinity (Km = 2.2 mM), low-capacity enzyme. UGT1A1 has intermediate affinity (9 mM) with high capacity, and UGT1A9 is a low-affinity, high-capacity enzyme (21 mM) (59). With a kinetic model, Court et al. estimated that at typical therapeutic concentrations (0.05-5 mM), UGT1A9 was the most important enzyme (>55% of total activity). Consequently, the mechanism of induction by oral contraceptives, phenytoin, and rifampin is unclear and may involve multiple enzymes. 

Other CYP3A4 inducers have also been reported to exert a pronounced effect on oral midazolam AUC (78), presumably through induction of intestinal and hepatic CYP3A4. For example, administration of phenytoin and carba-mazepine led to a 94% reduction in midazolam AUC compared with an untreated control population. Induction of CYP3A by St. John s wort, a widely used herbal supplement for the treatment of mild to moderate depression, has also attracted considerable interest. The major bioactive ingredient of St. John s wort, hyperforin, is a very potent in vitro activator of hPXR (79,80). Several groups have investigated induction of midazolam clearance by St. John s wort (81-83). As in the case of rifampin, clearance of oral midazolam... 

Inducers of UGT include carbamazepine, phenobarbital, phenytoin and rifampin. Inhibitors of UGTs include amitriptyline, chlorpromazine, ciclosporin, clomipramine, diazepam, lorazepam, nitrazepam and valproic acid,... 

LM is a 65-year-old woman with AF, a seizure disorder, and latent tuberculosis infection. LM s medications include digoxin, rifampin, calcium carbonate, phenytoin, and warfarin. Which of the following drugs can interfere with the oral absorption of T4 ... 

Drug interactions May decrease antihypertensive effects of ACE inhibitors, angiotensin II antagonists. May decrease antihypertensive and diuretic effects of thiazide and loop diuretics May decrease absorption of vitamin B,2 Effects decreased by barbiturates, phenytoin, and rifampin decreases effect of salicylates and vaccines Decreases clearance of beta-lactams Risk for hypersensitivity increased in patients who are on thiazides or ACE inhibitors and allopurinol... 

Drug interactions 5-HT3 antagonists are CYP450 substrates. Enzyme inducers (i.e., rifampin, phenytoin) may iixrease S-HTj antagonist clearance, and enzyme inhibitors (i.e, cimetidine, allopurinol) may increase toxichy. Metoclopramide and promethazine are CYP450 substrates. Drug clearance may be altered with concomitant use of enzyme inducers and inhibitors. 

Barbiturates, phenytoin, and rifampin induce hepatic metabolism of prednisone and thus decrease the effectiveness of prednisone. Prednisone decreases the effectiveness of vaccines and toxoids. ... 

Most abundant isoform wide substrate range inhibited by cimetidine, macrolides, azoles, and ethanol (acute) induced by general P450 inducers such as carbamazepine, phenobarbital, phenytoin, and rifampin and by ethanol (chronic). 

Barbiturates, phenytoin, and rifampin may cause decreased paramethasone effects because of increased hepatic metabolism. Cholestyramine, colestipol, and antacids decrease the corticosteroid effect by absorbing the corticosteroid, decreasing the amount absorbed. 

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