Drug Interactions between cyclosporine and Omeclamox-Pak

MONITOR CLOSELY: Coadministration with macrolide antibiotics that are potent inhibitors of CYP450 3A4 may significantly increase the blood concentrations of cyclosporine, which is primarily metabolized by the isoenzyme. The risk of nephro- and neurotoxicity associated with cyclosporine may be increased. There have been numerous reports of significant increases in cyclosporine peak concentration (Cmax) and systemic exposure (AUC) and decreases in its clearance during concomitant administration with macrolide antibiotics, especially erythromycin and clarithromycin. Macrolides that may significantly inhibit CYP450 3A4 include troleandomycin, erythromycin, and clarithromycin. Azithromycin and dirithromycin are generally believed to have little effect, if any, on CYP450 3A4, although azithromycin was implicated in a single case report.

MANAGEMENT: Caution is advised if cyclosporine is used with macrolide antibiotics that are potent inhibitors of CYP450 3A4. Cyclosporine blood levels and renal function should be checked frequently and the dosage adjusted accordingly, particularly following initiation or discontinuation of macrolide therapy in patients who are stabilized on their cyclosporine regimen. Patients should be advised to notify their doctor if they experience possible signs of cyclosporine toxicity such as nausea, vomiting, diarrhea, abdominal pain, dizziness, fatigue, headache, tremors, and convulsions. Alternative antibiotics that do not interfere with cyclosporine metabolism should be considered whenever possible.

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MONITOR: Chronic use of proton pump inhibitors (PPIs) may induce hypomagnesemia, and the risk may be increased during concomitant use of other agents that can cause magnesium loss such as cyclosporine. The mechanism via which hypomagnesemia may occur during long-term PPI use is unknown, although changes in intestinal absorption of magnesium may be involved. Hypomagnesemia has been reported rarely in patients treated with PPIs for at least three months, but in most cases, after a year or more. Serious adverse events include tetany, seizures, tremor, carpopedal spasm, atrial fibrillation, supraventricular tachycardia, and abnormal QT interval; however, patients do not always exhibit these symptoms. Hypomagnesemia can also cause impaired parathyroid hormone secretion, which may lead to hypocalcemia. In approximately 25% of the cases of PPI-associated hypomagnesemia reviewed by the FDA, the condition did not resolve with magnesium supplementation alone but also required discontinuation of the PPI. Both positive dechallenge as well as positive rechallenge (i.e., resolution of hypomagnesemia with PPI cessation and recurrence with PPI resumption) were reported in some cases. After discontinuing the PPI, the median time required for magnesium levels to normalize was one week. After restarting the PPI, the median time for hypomagnesemia to recur was two weeks.

MONITOR: Coadministration with omeprazole may alter the blood concentrations of cyclosporine in some patients. The mechanism of interaction is unknown. Both increased and decreased cyclosporine levels have been described in isolated case reports of patients treated concomitantly with omeprazole 40 mg/day. Moreover, one retrospective study found that the cyclosporine dosage required to achieve a certain therapeutic level was 28% lower in heart transplant patients who received omeprazole (n=21) than in those who did not (n=139). In contrast, two pharmacokinetic studies have found no significant interaction between these two agents. In 10 male kidney transplant patients with stable renal function receiving maintenance cyclosporine therapy, omeprazole administered at 20 mg once daily for two weeks had no clinically or statistically significant effect on the whole blood concentrations of cyclosporine and its metabolites relative to placebo. In addition, no adverse event and no clinically significant changes in laboratory values were noted during administration of omeprazole. Likewise, no significant changes in cyclosporine levels were observed in eight kidney transplant patients administered omeprazole 20 mg/day for six days compared to controls.

MANAGEMENT: Monitoring of serum magnesium levels is recommended prior to initiation of therapy and periodically thereafter if prolonged treatment with a proton pump inhibitor is anticipated or when combined with other agents that can cause hypomagnesemia such as cyclosporine. Patients should be advised to seek immediate medical attention if they develop potential signs and symptoms of hypomagnesemia such as palpitations, arrhythmia, muscle spasm, tremor, or convulsions. In children, abnormal heart rates may cause fatigue, upset stomach, dizziness, and lightheadedness. Magnesium replacement as well as discontinuation of the PPI may be required in some patients. A potential interaction with omeprazole should also be considered when cyclosporine levels are altered and no other causes can be identified. Occasionally, a dosage adjustment of cyclosporine may be necessary.

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Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

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Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.

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