Drug Interactions between Abraxane and doxycycline

MONITOR: Coadministration with inhibitors of CYP450 3A4, such as grapefruit juice, may increase the plasma concentrations of paclitaxel, which is a substrate of the isoenzyme. Current data suggest that consumption of large quantities of grapefruit juice inhibit both intestinal and hepatic CYP450 3A4 due to certain compounds present in grapefruit. Specific data for paclitaxel are lacking; however, in a case report of a 52-year-old woman with esophageal squamous cell carcinoma receiving a twice weekly chemotherapy regimen including intravenous docetaxel (40 mg/m2) reported that docetaxel systemic exposure (AUC) increased by 65% compared with the AUC target of 1.96 mg*h/L and clearance decreased by 63%, with a 71% reduction in the patient's neutrophil count. In the absence of other CYP450 3A4 inhibitors, these effects were attributed to daily consumption of 250 mL of grapefruit juice, which the patient had been consuming for at least 3 months. Two weeks after the patient ceased the grapefruit juice, the docetaxel AUC was closer to the target value and the neutrophil count reduction was less than 35%. In addition, in a pharmacokinetic study consisting of 7 cancer patients, mean dose-normalized docetaxel AUC increased by 2.2-fold and clearance decreased by 49% when intravenous docetaxel was given at a reduced dosage of 10 mg/m2 in combination with the potent CYP450 3A4 inhibitor ketoconazole (200 mg orally once daily for 3 days) compared to docetaxel administered alone at 100 mg/m2.

MANAGEMENT: Caution is recommended if paclitaxel is to be used in combination with grapefruit and grapefruit juice. Patients should be closely monitored for the development of paclitaxel toxicity, including diarrhea, mucositis, myelosuppression, and peripheral neuropathy and dose adjustment considered per local treatment protocols.

GENERALLY AVOID: The bioavailability of oral tetracyclines and iron salts may be significantly decreased during concurrent administration. Therapeutic failure may result. The proposed mechanism is chelation of tetracyclines by the iron cation, forming an insoluble complex that is poorly absorbed from the gastrointestinal tract. In ten healthy volunteers, simultaneous oral administration of ferrous sulfate 200 mg and single doses of various tetracyclines (200 mg to 500 mg) resulted in reductions in the serum levels of methacycline and doxycycline by 80% to 90%, oxytetracycline by 50% to 60%, and tetracycline by 40% to 50%. In another study, 300 mg of ferrous sulfate reduced the absorption of tetracycline by 81% and that of minocycline by 77%. Conversely, the absorption of iron has been shown to be decreased by up to 78% in healthy subjects and up to 65% in patients with iron depletion when ferrous sulfate 250 mg was administered with tetracycline 500 mg. Available data suggest that administration of iron 3 hours before or 2 hours after a tetracycline largely prevents the interaction with most tetracyclines except doxycycline. Due to extensive enterohepatic cycling, iron binding may occur with doxycycline even when it is given parenterally. It has also been shown that when iron is administered up to 11 hours after doxycycline, serum concentrations of doxycycline may still be reduced by 20% to 45%.

MANAGEMENT: Coadministration of a tetracycline with any iron-containing product should be avoided if possible. Otherwise, patients should be advised to stagger the times of administration by at least three to four hours, although separating the doses may not prevent the interaction with doxycycline.

Chronic alcohol consumption may enhance the elimination of doxycycline. The mechanism is induction of hepatic microsomal enzymes by alcohol. In one study, the half-life of doxycycline in six alcoholics was 10.5 hours, compared with 14.7 hours in six control patients. In addition, half the alcoholic patients had serum concentrations below what is generally considered the minimum therapeutic concentration (0.5 mcg/mL) at 12 to 24 hours after the dose. The investigators suggest that twice-a-day dosing may be indicated in these patients, especially if additional inducing drugs are used. The elimination of other tetracyclines probably is not affected by alcohol consumption.