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Roxithromycin DNA Dosage |
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Susceptible infections
Adult: 150 mg bid or 300 mg once daily for 5-10 days in susceptible infections.
Child: 6-40 kg: 5-8 mg/kg daily.
Renal impairment: Dosage adjustment may be required.
Hepatic impairment: Usual daily doses should be halved in hepatic impairment.
Roxithromycin DNA has a much lower affinity for cytochrome P450 than
erythromycin, and consequently has fewer interactions. Interactions may be
observed, however, with drugs that bind to alpha-1-acid glycoprotein, e.g.
disopyramide.
Roxithromycin DNA does not appear to interact with oral contraceptives,
prednisolone, carbamazepine, ranitidine or antacids.
Theophylline. A study in normal subjects concurrently administered
Roxithromycin DNA and theophylline has shown some increase in the plasma
concentration of the latter. While a change in dosage is usually not required,
patients with high levels of theophylline at commencement of treatment
should have levels monitored.
Ergot alkaloids. Reactions of ergotism with possible peripheral necrosis have
been reported after concomitant therapy of macrolides with vasoconstrictive ergot alkaloids, particularly ergotamine and dihydroergotamine. Because a
clinical interaction with Roxithromycin DNA cannot be excluded, administration of
Roxithromycin DNA to patients taking ergot alkaloids is contraindicated.
Disopyramide. An in vitro study has shown that Roxithromycin DNA can displace
protein bound disopyramide; such an effect in vivo could result in increased
serum levels of disopyramide. Consequently, ECG and, if possible,
disopyramide serum levels should be monitored.
Terfenadine. Some macrolide antibiotics (e.g. erythromycin) may increase
serum levels of terfenadine. This can result in severe cardiovascular adverse
events, including QT prolongation, torsades de pointes and other ventricular
arrhythmias. Such a reaction has not been documented with Roxithromycin DNA,
which has a much lower affinity for cytochrome P450 than erythromycin.
However, in the absence of a systematic interaction study, concomitant
administration of Roxithromycin DNA and terfenadine is not recommended.
Astemizole, cisapride, pimozide. Other drugs, such as astemizole, cisapride
or pimozide, which are metabolised by the hepatic isozyme CYP3A4, have
been associated with QT interval prolongation and/or cardiac arrhythmias
(typically torsades de pointes) as a result of an increase in their serum level
subsequent to interaction with significant inhibitors of this isozyme, including
some macrolide antibacterials. Although Roxithromycin DNA has no or limited ability
to complex CYP3A4 and hence to inhibit the metabolism of other drugs
processed by this isozyme, a potential for clinical interaction of Roxithromycin DNA
with the above mentioned drugs cannot be either ascertained or ruled out in
confidence. Thus, concomitant administration of Roxithromycin DNA and such drugs
is not recommended.
Warfarin. While no interaction was observed in volunteer studies,
Roxithromycin DNA appears to interact with warfarin. Increases in prothrombin time
(international normalised ratio (INR)) have been reported in patients treated
concomitantly with Roxithromycin DNA and warfarin or the related vitamin K
antagonist phenprocoumon, and severe bleeding episodes have occurred as
a consequence.
Digoxin and other cardiac glycosides. A study in healthy volunteers has
shown that Roxithromycin DNA may increase the absorption of digoxin. This effect,
common to other macrolides, may very rarely result in cardiac glycoside
toxicity. This may be manifested by symptoms such as nausea, vomiting,
diarrhoea, headache or dizziness. Cardiac glycoside toxicity may also elicit
heart conduction and/or rhythm disorders. Consequently, in patients treated
with Roxithromycin DNA and digoxin or another cardiac glycoside, ECG and, if
possible, the serum level of the cardiac glycoside should be monitored. This is
mandatory if symptoms suggesting cardiac glycoside overdosage have
occurred.
Midazolam. Roxithromycin DNA, like other macrolides, may increase the area
under the midazolam concentration-time curve and the midazolam half-life.
Thus, the effects of midazolam may be enhanced and prolonged in patients treated with Roxithromycin DNA. There is no conclusive evidence for an interaction
between Roxithromycin DNA and triazolam.
Cyclosporin. A slight increase in plasma concentrations of cyclosporin A has
been observed. This does not generally necessitate altering the usual dosage.
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Information checked by Dr. Sachin Kumar, MD Pharmacology
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