Roxithromycin metabolism

Nefazodone substantially decreases the clearance rate for triazolam, which results in a 400% increase in triazolam s serum levels (131). Erythromycin can also interfere with the metabolism of triazolam, resulting in decreased clearance and increased plasma levels, possibly causing toxicity. Troleandomycin and other macrolide antibiotics, such as clarithromycin, flurithromycin, josamycin, midecamycin, or roxithromycin, also may inhibit triazolam s metabolism (132). The coadministration of itraconazoie and triazolam can produce a marked elevation of triazolam plasma levels associated with statistically significant impairment of psychomotor tests and a prolongation of other effects (e.g., amnesia, lethargy, and confusion) for hours after awakening ( 133). 

Roxithromycin has been shown to be metabolized in vivo to form several metabolites, including a decladinosyl derivative (Ml), O-dealkyl derivative (M2), A -monodemethyl derivative (M3), and didemethyl derivative (M4) in rats, dogs, and humans (Fig. 2) [34, 35]. In human plasma, only roxithromycin was detected [25]. 

Erythromycin is a known inhibitor of the cytochrome P450 isoenzyme CYP3A4. However, this isoenzyme has only a minor role in the metabolism of warfarin , (p.358), specifically the less active R-isomer of warfarin. Consequently, only minor increases in the levels of warfarin have been seen in pharmacokinetic studies, which would generally not be expected to be clinically relevant. However, it is possible that even these small changes might be important in a very few patients, particularly those with a low prothrombin complex aetivity. Other macrolides (azithromycin, clarithromycin, dirithromycin, roxithromycin) have less effect on CYP3A4 than erythromycin, and consequently would be expected to have even less effect on the pharmacokinetics of warfarin or acenocoumarol, which is borne out in the few studies available. Nevertheless, cases of interactions have been reported for nearly all these macrolides. Moreover, one cohort study found that clarithromycin increased the risk of an interaction and erythromycin did not. It is possible that there is some other, as yet unidentified, mechanism involved. Alternatively, it is equally possible that the relatively few cases just represent idiosyncratic effects attributable to other factors, and not to any interaction (see also Coumarins -i- Antibacterials , p.365). 

It seems probable that clarithromycin, erythromycin and troleandomycin, and to a lesser extent some of the other macrolides, slow the rate of metabolism of the carbamazepine by the cytochrome P450 isoenzyme CYP3A4 so that the anticonvulsant accumulates within the body." " Telithromycin is predicted to interact similarly." It was suggested that the carbamazepine toxicity seen with roxithromycin may have been mediated by P-glycoprotein inhibition, which occurred as a result of an interaction between roxithromycin and atorvastatin. 

Not known, but it could be that clarithromycin inhibits the metabolism of the phenytoin by the liver. An animal study found that erythromycin, clarithromycin, and roxithromycin reduced the metabolism and increased levels of phenytoin. ... 

It is believed that troleandomycin forms inactive cytochrome P450-metab-olite complexes within the liver, the effect of which is to reduce the metabolism (A/-demethylation and 8-hydroxylation) of theophylline, thereby reducing its clearance and increasing its levels. Clarithromycin, josamycin, midecamycin, and roxithromycin are thought to rarely form complexes, and azithromycin, dirithromycin, rokitamycin and spiramycin are not thought to inactivate cytochrome P450. ... 

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