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Drug Interactions between doxazosin and itraconazole

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

itraconazole doxazosin

Applies to: itraconazole and doxazosin

MONITOR: Coadministration with potent inhibitors of CYP450 3A4 may increase the plasma concentrations and effects of doxazosin. In vitro studies suggest that the primary pathway for elimination of doxazosin is via CYP450 3A4.

MANAGEMENT: Caution is advised if doxazosin is used concomitantly with potent CYP450 3A4 inhibitors. Blood pressure and pharmacologic response to doxazosin should be monitored closely whenever a potent CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the doxazosin dosage adjusted if necessary. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, orthostasis, syncope, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medication affects them.

References

  1. (2001) "Product Information. Cardura (doxazosin)." Pfizer U.S. Pharmaceuticals
  2. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  3. Canadian Pharmacists Association (2006) e-CPS. http://www.pharmacists.ca/function/Subscriptions/ecps.cfm?link=eCPS_quikLink

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Drug and food interactions

Moderate

itraconazole food

Applies to: itraconazole

ADJUST DOSING INTERVAL: Food increases the absorption of itraconazole capsules but decreases the absorption of itraconazole oral solution. Cola beverages may increase the bioavailability of itraconazole capsules. Itraconazole capsules require an acidic gastric pH for adequate dissolution and subsequent absorption. Cola beverages help lower gastric pH and improve absorption.

GENERALLY AVOID: Grapefruit juice may impair the absorption of itraconazole capsules, resulting in decreased antifungal effects. In a small, randomized, crossover study, the administration of itraconazole capsules with double-strength grapefruit juice (compared to water) was associated with significantly decreased (43%) plasma concentrations of itraconazole and its pharmacologically active hydroxy metabolite, as well as delayed times to reach peak concentrations of both. The exact mechanism of interaction is unknown but may involve reduced absorption of itraconazole secondary to enhanced activity of intestinal P-glycoprotein drug efflux pumps and delayed gastric emptying induced by certain compounds present in grapefruits. Another study reported no pharmacokinetic changes with single-strength grapefruit juice. Whether or not these observations apply to itraconazole oral solution is unknown.

MANAGEMENT: The manufacturer recommends that the capsules be taken immediately after a full meal and the solution be taken on an empty stomach to ensure maximal absorption. Cola beverages may help increase the bioavailability of itraconazole capsules, particularly in patients with hypochlorhydria or those treated concomitantly with gastric acid suppressants. Until more information is available, it may be advisable to avoid the consumption of grapefruits and grapefruit juice during itraconazole therapy.

References

  1. Van Peer A, Woestenborghs R, Heykants J, et al. (1989) "The effects of food and dose on the oral systemic availability of itraconazole in healthy subjects." Eur J Clin Pharmacol, 36, p. 423-6
  2. Wishart JM (1987) "The influence of food on the pharmacokinetics of itraconazole in patients with superficial fungal infection." J Am Acad Dermatol, 17, p. 220-3
  3. (2002) "Product Information. Sporanox (itraconazole)." Janssen Pharmaceuticals
  4. Barone JA, Koh JG, Bierman RH, Colaizzi JL, Swanson KA, Gaffar MC, Moskovitz BL, Mechlinski W, Van de Velde V (1993) "Food interaction and steady-state pharmacokinetics of itraconazole capsules in healthy male volunteers." Antimicrob Agents Chemother, 37, p. 778-84
  5. Zimmermann T, Yeates RA, Albrecht M, Laufen H, Wildfeuer A (1994) "Influence of concomitant food intake on the gastrointestinal absorption of fluconazole and itraconazole in japanese subjects." Int J Clin Pharmacol Res, 14, p. 87-93
  6. (2022) "Product Information. Sporanox (itraconazole)." Janssen Pharmaceuticals
  7. Kawakami M, Suzuki K, Ishizuka T, Hidaka T, Matsuki Y, Nakamura H (1998) "Effect of grapefruit juice on pharmacokinetics of itraconazole in healthy subjects." Int J Clin Pharmacol Ther, 36, p. 306-8
  8. Barone JA, Moskotitz BL, Guarnieri J, Hassell AE, Colaizzi JL, Bierman RH, Jessen L (1998) "Food interaction and steady-state pharmacokinetics of itraconazole oral solution in healthy volunteers." Pharmacotherapy, 18, p. 295-301
  9. Penzak SR, Gubbins PO, Gurley BJ, Wang PL, Saccente M (1999) "Grapefruit juice decreases the systemic availability of itraconazole capsules in healthy volunteers." Ther Drug Monit, 21, p. 304-9
  10. Katz HI (1999) "Drug interactions of the newer oral antifungal agents." Br J Dermatol, 141, p. 26-32
View all 10 references

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Moderate

doxazosin food

Applies to: doxazosin

GENERALLY AVOID: The concurrent use of ethanol and alpha-1 adrenergic blockers may cause increased hypotensive effects. Patients with aldehyde dehydrogenase deficiencies (primarily Asians) may be at a higher risk of this interaction. The mechanism has not been determined. Data exist for prazosin and other alpha adrenergic blockers are expected to interact also. In addition, any patients taking alpha adrenergic blockers may experience excessive orthostatic hypotension with ethanol ingestion, due to ethanol's unopposed vasodilatory effects in the presence of alpha adrenergic blockade.

MANAGEMENT: Patients who develop a flushing reaction after ethanol ingestion (indicates a possible aldehyde dehydrogenase deficiency) should be advised to avoid ethanol or limit their intake. All patients should be warned about the possibility of orthostatic hypotension with concurrent ethanol use.

References

  1. Kawano Y, Abe H, Kojima S, Takishita S, Omae T (2000) "Interaction of alcohol and an a1-blocker on ambulatory blood pressure in patients with essential hypertension." Am J Hypertens, 13, p. 307-12
  2. (2002) "Product Information. Xatral (alfuzosin)." Sanofi-Synthelabo Canada Inc

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Therapeutic duplication warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

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