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Drug Interactions between Dilt-XR and tizanidine

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

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Interactions between your drugs

Major

dilTIAZem tiZANidine

Applies to: Dilt-XR (diltiazem) and tizanidine

ADJUST DOSE: Tizanidine may potentiate the hypotensive effect of some medications secondary to its alpha-2 adrenergic activity. Pharmacologic studies have found tizanidine to possess between 1/10 to 1/50 of the potency of clonidine, a structurally similar agent, in lowering blood pressure. The hypotensive effect of tizanidine is dose-related and has been measured following single doses of 2 mg or more. In a single-dose study where blood pressure was monitored closely after dosing, two-thirds of patients treated with an 8 mg dose had a 20% reduction in either diastolic or systolic blood pressure. The reduction was seen within 1 hour after dosing, peaked 2 to 3 hours after dosing, and was associated at times with bradycardia, orthostatic hypotension, lightheadedness, dizziness, and rarely, syncope. In clinical trials, the addition of tizanidine to antihypertensive therapy was associated with a 20% to 30% increase in the incidence of clinically significant decreases in systolic or diastolic blood pressure compared with placebo plus antihypertensive therapy or tizanidine alone. The incidence of orthostatic hypotension was also increased.

MANAGEMENT: A lower initial dosage and cautious dosage titration should be considered when tizanidine is initiated in patients receiving hypotensive medications. Although single doses of less than 8 mg of tizanidine have not been shown to be effective for spasticity in controlled clinical studies, some authorities recommend initiating treatment with single oral doses of 2 mg. The dose can then be gradually increased by 2 to 4 mg, with 1 to 4 days between dosage increases, until the optimum effect is achieved. The dose can be repeated at 6- to 8-hour intervals as needed, up to a maximum of three doses in 24 hours and a total daily dosage of 36 mg. Single doses greater than 16 mg have not been studied. Close monitoring for development of hypotension is recommended. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia.

References

  1. "Product Information. Zanaflex (tizanidine)." Acorda Therapeutics PROD (2001):
  2. "Product Information. TiZANidine Hydrochloride (tiZANidine)." Advagen Pharma Limited (2019):
  3. "Product Information. Apo-TiZANidine (tizanidine)." AA Pharma Inc (2023):
  4. "Product Information. Tizagelan (tizanidine)." G.L. Pharma UK Ltd (2022):
View all 4 references

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Drug and food interactions

Moderate

dilTIAZem food

Applies to: Dilt-XR (diltiazem)

MONITOR: Like many CNS-active agents, alcohol can exhibit hypotensive effects. Coadministration with antihypertensive agents including diltiazem may result in additive effects on blood pressure and orthostasis.

MONITOR: Grapefruit juice may increase the plasma concentrations of orally administered diltiazem in some patients. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. In a study of ten healthy male volunteers, administration of a single 120 mg oral dose of immediate-release diltiazem in combination with 250 mL of grapefruit juice increased the diltiazem peak plasma concentration (Cmax) and systemic exposure (AUC) by an average of 22% and 20%, respectively, compared to administration with water. The time to reach Cmax (Tmax) and the terminal half-life were not affected, and no statistically significant differences in blood pressure and heart rate were observed during administration with grapefruit juice relative to water. In a different study, repeated administration of 200 mL of grapefruit juice at 0, 2, 4, 8 and 12 hours had no significant effect on the Cmax or AUC of a single 120 mg oral dose of diltiazem, but increased its half-life from 4.1 to 5.1 hours. The ratios for the N-demethyl and deacetyl metabolites to diltiazem were also not affected by grapefruit juice. However, because pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability, the extent to which a given patient may be affected is difficult to predict.

MANAGEMENT: Patients should be advised that alcohol may potentiate the hypotensive effects of diltiazem, especially during the initiation of therapy and following a dosage increase. Caution should be exercised when rising from a sitting or recumbent position, and patients should notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients who regularly consume grapefruit or grapefruit juice should be monitored for increased adverse effects of diltiazem such as such as headache, irregular heartbeat, edema, unexplained weight gain, and chest pain. Grapefruit and grapefruit juice should be avoided if an interaction is suspected.

References

  1. Bailey DG, Arnold JMO, Spence JD "Grapefruit juice and drugs - how significant is the interaction." Clin Pharmacokinet 26 (1994): 91-8
  2. Sigusch H, Henschel L, Kraul H, Merkel U, Hoffmann A "Lack of effect of grapefruit juice on diltiazem bioavailability in normal subjects." Pharmazie 49 (1994): 675-9
  3. Bailey DG, Malcolm J, Arnold O, Spence JD "Grapefruit juice-drug interactions." Br J Clin Pharmacol 46 (1998): 101-10
  4. Christensen H, Asberg A, Holmboe AB, Berg KJ "Coadministration of grapefruit juice increases systemic exposure of diltiazem in healthy volunteers." Eur J Clin Pharmacol 58 (2002): 515-520
  5. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
View all 5 references

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Moderate

dilTIAZem food

Applies to: Dilt-XR (diltiazem)

MONITOR: Calcium-containing products may decrease the effectiveness of calcium channel blockers by saturating calcium channels with calcium. Calcium chloride has been used to manage acute severe verapamil toxicity.

MANAGEMENT: Management consists of monitoring the effectiveness of calcium channel blocker therapy during coadministration with calcium products.

References

  1. Henry M, Kay MM, Viccellio P "Cardiogenic shock associated with calcium-channel and beta blockers: reversal with intravenous calcium chloride." Am J Emerg Med 3 (1985): 334-6
  2. Moller IW "Cardiac arrest following intravenous verapamil combined with halothane anaesthesia." Br J Anaesth 59 (1987): 522-6
  3. Oszko MA, Klutman NE "Use of calcium salts during cardiopulmonary resuscitation for reversing verapamil-associated hypotension." Clin Pharm 6 (1987): 448-9
  4. Schoen MD, Parker RB, Hoon TJ, et al. "Evaluation of the pharmacokinetics and electrocardiographic effects of intravenous verapamil with intravenous calcium chloride pretreatment in normal subjects." Am J Cardiol 67 (1991): 300-4
  5. O'Quinn SV, Wohns DH, Clarke S, Koch G, Patterson JH, Adams KF "Influence of calcium on the hemodynamic and anti-ischemic effects of nifedipine observed during treadmill exercise testing." Pharmacotherapy 10 (1990): 247
  6. Woie L, Storstein L "Successful treatment of suicidal verapamil poisoning with calcium gluconate." Eur Heart J 2 (1981): 239-42
  7. Morris DL, Goldschlager N "Calcium infusion for reversal of adverse effects of intravenous verapamil." JAMA 249 (1983): 3212-3
  8. Guadagnino V, Greengart A, Hollander G, Solar M, Shani J, Lichstein E "Treatment of severe left ventricular dysfunction with calcium chloride in patients receiving verapamil." J Clin Pharmacol 27 (1987): 407-9
  9. Luscher TF, Noll G, Sturmer T, Huser B, Wenk M "Calcium gluconate in severe verapamil intoxication." N Engl J Med 330 (1994): 718-20
  10. Bar-Or D, Gasiel Y "Calcium and calciferol antagonise effect of verapamil in atrial fibrillation." Br Med J (Clin Res Ed) 282 (1981): 1585-6
  11. Lipman J, Jardine I, Roos C, Dreosti L "Intravenous calcium chloride as an antidote to verapamil-induced hypotension." Intensive Care Med 8 (1982): 55-7
  12. McMillan R "Management of acute severe verapamil intoxication." J Emerg Med 6 (1988): 193-6
  13. Perkins CM "Serious verapamil poisoning: treatment with intravenous calcium gluconate." Br Med J 2 (1978): 1127
  14. Moroni F, Mannaioni PF, Dolara A, Ciaccheri M "Calcium gluconate and hypertonic sodium chloride in a case of massive verapamil poisoning." Clin Toxicol 17 (1980): 395-400
View all 14 references

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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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