Drug Interactions between fexinidazole and Terramycin IM

MONITOR: Grapefruit and grapefruit juice may increase the plasma concentrations of lidocaine, which is primarily metabolized by the CYP450 3A4 and 1A2 isoenzymes to active metabolites (monoethylglycinexylidide (MEGX) and glycinexylidide). The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice but has been reported with oral and/or intravenous lidocaine and potent CYP450 3A4 inhibitor, itraconazole, as well as moderate CYP450 3A4 inhibitor, erythromycin. A pharmacokinetic study of 9 healthy volunteers showed that the administration of lidocaine oral (1 mg/kg single dose) with itraconazole (200 mg daily) increased lidocaine systemic exposure (AUC) and peak plasma concentration (Cmax) by 75% and 55%, respectively. However, no changes were observed in the pharmacokinetics of the active metabolite MEGX. In the same study, when the moderate CYP450 3A4 inhibitor erythromycin (500 mg three times a day) was administered, lidocaine AUC and Cmax increased by 60% and 40%, respectively. By contrast, when intravenous lidocaine (1.5 mg/kg infusion over 60 minutes) was administered on the fourth day of treatment with itraconazole (200 mg once a day) no changes in lidocaine AUC or Cmax were observed. However, when lidocaine (1.5 mg/kg infusion over 60 minutes) was coadministered with erythromycin (500 mg three times a day) in the same study, the AUC and Cmax of the active metabolite MEGX significantly increased by 45-60% and 40%, respectively. The observed differences between oral and intravenous lidocaine when coadministered with CYP450 3A4 inhibitors may be attributed to inhibition of CYP450 3A4 in both the gastrointestinal tract and liver affecting oral lidocaine to a greater extent than intravenous lidocaine. In general, the effects of grapefruit products are concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. While the clinical significance of this interaction is unknown, increased exposure to lidocaine may lead to serious and/or life-threatening reactions including respiratory depression, convulsions, bradycardia, hypotension, arrhythmias, and cardiovascular collapse.

MONITOR: Certain foods and behaviors that induce CYP450 1A2 may reduce the plasma concentrations of lidocaine. The proposed mechanism is induction of hepatic CYP450 1A2, one of the isoenzymes responsible for the metabolic clearance of lidocaine. Cigarette smoking is known to be a CYP450 1A2 inducer. In one pharmacokinetic study of 4 smokers and 5 non-smokers who received 2 doses of lidocaine (100 mg IV followed by 100 mg orally after a 2-day washout period), the smokers' systemic exposure (AUC) of oral lidocaine was 68% lower than non-smokers. The AUC of IV lidocaine was only 9% lower in smokers compared with non-smokers. Other CYP450 1A2 inducers include cruciferous vegetables (e.g., broccoli, brussels sprouts) and char-grilled meat. Therefore, eating large or variable amounts of these foods could also reduce lidocaine exposure. The clinical impact of smoking and/or the ingestion of foods that induce CYP450 1A2 on lidocaine have not been studied, however, a loss of efficacy may occur.

MANAGEMENT: Caution is recommended if lidocaine is to be used in combination with grapefruit and grapefruit juice. Monitoring for lidocaine toxicity and plasma lidocaine levels may also be advised, and the lidocaine dosage adjusted as necessary. Patients who smoke and/or consume cruciferous vegetables may be monitored for reduced lidocaine efficacy.

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ADJUST DOSING INTERVAL: Administration with food, particularly dairy products, significantly reduces tetracycline absorption. The calcium content of these foods forms nonabsorbable chelates with tetracycline.

MANAGEMENT: Tetracycline should be administered one hour before or two hours after meals.

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GENERALLY AVOID: Use of alcohol or products containing alcohol during nitroimidazole therapy may result in a disulfiram-like reaction in some patients. There have been a few case reports involving metronidazole, although data overall are not convincing. The presumed mechanism is inhibition of aldehyde dehydrogenase (ALDH) by metronidazole in a manner similar to disulfiram. Following ingestion of alcohol, inhibition of ALDH results in increased concentrations of acetaldehyde, the accumulation of which can produce an unpleasant physiologic response referred to as the 'disulfiram reaction'. Symptoms include flushing, throbbing in head and neck, throbbing headache, respiratory difficulty, nausea, vomiting, sweating, thirst, chest pain, palpitation, dyspnea, hyperventilation, tachycardia, hypotension, syncope, weakness, vertigo, blurred vision, and confusion. Severe reactions may result in respiratory depression, cardiovascular collapse, arrhythmia, myocardial infarction, acute congestive heart failure, unconsciousness, convulsions, and death. However, some investigators have questioned the disulfiram-like properties of metronidazole. One study found neither elevations in blood acetaldehyde nor objective or subjective signs of a disulfiram-like reaction to ethanol in six subjects treated with metronidazole (200 mg three times a day for 5 days) compared to six subjects who received placebo.

GENERALLY AVOID: The potential exists for pharmacodynamic interactions and/or toxicities between fexinidazole and herbal medicines and supplements. In addition, grapefruit and grapefruit juice may, theoretically, increase the plasma concentrations of fexinidazole and the risk of adverse effects. The mechanism is decreased clearance of fexinidazole due to inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict.

ADJUST DOSING INTERVAL: Food significantly increases the oral absorption and bioavailability of fexinidazole. Compared with the fasted state, the systemic exposure (AUC) of fexinidazole and its metabolites (fexinidazole sulfoxide [M1], fexinidazole sulfone [M2]) were 4- to 5-fold higher following administration with food.

MANAGEMENT: To ensure maximal oral absorption, fexinidazole should be administered with food each day at about the same time of day (e.g., during or immediately after the main meal of the day). Coadministration of fexinidazole with grapefruit, grapefruit juice, or herbal medicines or supplements should be avoided. Because clear evidence is lacking concerning the safety of ethanol use during nitroimidazole therapy, patients should be apprised of the potential for interaction and instructed to avoid alcoholic beverages and products containing alcohol or propylene glycol while using oral, intravenous, or vaginal preparations of a nitroimidazole. Alcoholic beverages should not be consumed for at least 48 hours after completion of fexinidazole therapy.

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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.

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