Dexamethasone manufacturers

Enzyme inducers. The effects of the enzyme inducers carbamazepine, dexamethasone, phenytoin and rifampicin have not been studied with parecoxib. Nevertheless, the manufacturer of parecoxib warns that they may increase the metabolism of valdecoxib. ... 

As parecoxib is rapidly metabolised to valdecoxib, the interactions are usually considered to be due to the effects of valdecoxib. The manufacturer of parecoxib cautions the concurrent use with carbamazepine, dexamethasone and rifampicin as their effects on parecoxib have not been studied. Valdecoxib increases the levels of dextromethorphan and omeprazole. Because of these interactions, caution is advised with drugs that are metabolised by the same isoenzymes, nameiy flecainide, metoprolol, propafenone, omeprazoie, diazepam, imipramine and phenytoin. No interaction appears to occur between parecoxib and midazolam. 

The UK manufacturers point out that carbamazepine, dexamethasone, phenobarbital, phenytoin and rifampicin are all inducers of CYP3A4, an isoenzyme involved in the metabolism of sibutramine. These drugs might therefore increase the metabolism of sibutramine resulting in a fall in its serum levels. However, this has not been studied experimentally and, at the present time, the existence, the extent and the possible clinical relevance of any such interaction is unknown. 

No specific studies have been carried out with imatinib and other CYP3A4-inducing drugs, but the manufacturers suggest that carbamazepine, dexamethasone, phenobarbital, and phenytoin, may also reduce imatinib serum levels, and they have a possible case on file with phenytoin. The manufacturers therefore reasonably recommend caution, and suggest that concurrent use with these drugs should be avoided. However, if this is not possible it would be prudent to monitor the outcome of concurrent use, and increase the imatinib dose as necessary. 

On the basis of an in vitro study using human liver sliees and human liver mierosomes it has been coneluded that the metabolism of paclitaxel is unlikely to be altered by cimetidine, dexamethasone or diphenhydramine, all of which are frequently given to prevent the hypersensitivity reactions associated with paclitaxel or its vehicle, Cremophor (see b, below). The UK manufacturers say that paclitaxel clearance in patients is not affected by cimetidine premedication, although some authors have advised caution when using cimetidine with docetaxel or paclitaxel since cimetidine is known to affect the cytochrome P450 isoenzyme CYP3A4, which is responsible, in part, for the metabolism of these taxanes. 

The manufacturer notes that concurrent use of carbamazepine, dexamethasone, H2-receptor antagonists, ondansetron, phenobarbital, phenytoin or prochlorperazine did not affect the clearance of temozolomide, based on an analysis of population pharmacokinetics from phase II studies. However, valproic acid modestly reduced the clearance of temozolomide. 

Information seems to be limited to these studies. The indication is that large doses of some antacids can reduce the bioavailability of corticosteroids, but small doses do not, although this needs confirmation. One manufacturer of dexamethasone suggests that the doses of antacid should be spaced as far as possible from the dexamethasone, while another suggests an interval of at least 2 hours. In other similar antacid interactions 2 to 3 hours is usually sufficient. The manufacturers of deflazacort also suggest an interval of at least 2 hours between administration of deflazacort and antacids. " Concurrent use should be monitored to confirm that the therapeutic response is adequate. Information about the interaction of other corticosteroids and antacids is lacking. 

An established interaction of clinical importance. The manufacturer recommends that the usual dose of dexamethasone should be reduced by about 50% when given with aprepitant (although note that the dose given... 

Ritonavir may increase the levels of prednisone and some manufacturers of betamethasone, budesonide, ciclesonide, or dexamethasone predict a similar interaction with ritonavir or nelfinavir. . 

The manufacturers of dexamethasone note that it is a modest inducer of CYP3A4 and state that it may reduce the plasma levels of indinavir, and saquinavir, or other drugs metabolised by CYP3A4. The clinical outcome of this predicted effect is unknown, but until more is known, it would seem prudent to monitor antiviral efficacy if these combinations are used. 

Many synthetic corticoids were introduced following the discovery of triamcinolone. These include triamcinolone 16,17-acetonide, 6o -methylprednisolone, 16a -methyl-9o -fluoroprednisolone (dexamethasone), 16 -methyl-9a(-fluoroprednisolone (betamethasone), 6o -fluoro-16a-methylprednisolone (paramethasone), 16-methylene-prednisolone, and 6a, 9a -dlfluoro-16a-hydroxyprednisolone 16,17-acetonide (fluocino-lone acetonide). Microbiology played no essential role in their discovery, although in some cases microbiological technology has been employed to advantage in their manufacture. 

---