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Drug Interactions between Mellaril-S and QM-260

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

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Interactions between your drugs

Major

quiNINE thioridazine

Applies to: QM-260 (quinine) and Mellaril-S (thioridazine)

CONTRAINDICATED: Coadministration with inhibitors of CYP450 2D6 may increase the plasma concentrations and adverse effects of thioridazine and its two active metabolites, mesoridazine and sulforidazine, all of which are substrates of the isoenzyme. A study in 19 healthy male patients reviewed thioridazine metabolism in 6 slow and 13 rapid hydroxylators of debrisoquin (the rate of which is believed to be dependent upon the level of CYP450 2D6 activity). A single oral dose of thioridazine (25 mg) produced a 2.4-fold higher peak plasma concentration (Cmax) and a 4.5-fold higher systemic exposure (AUC) for thioridazine in the slow hydroxylators, which is predicted to be similar to what would be seen in patients on CYP450 2D6 inhibitors. Additionally, significant increases (up to severalfold) have been observed during coadministration with fluvoxamine, propranolol, and pindolol in pharmacokinetic studies, although these reductions in clearance may be via other currently unknown mechanisms. The use of thioridazine has been associated with dose-related prolongation of the QT interval, thus elevated plasma levels of the drug may potentiate the risk of ventricular arrhythmias such as ventricular tachycardia and torsade de pointes as well as cardiac arrest and sudden death. Several cases of torsade de pointes have been reported.

MANAGEMENT: The use of thioridazine with fluvoxamine, propranolol, pindolol and/or drugs that inhibit CYP450 2D6 is considered contraindicated. Depending on the elimination half-life of these drugs, a considerable waiting period may be appropriate following their discontinuation before thioridazine is initiated. For example, the manufacturer of fluoxetine recommends that thioridazine not be administered within 5 weeks after discontinuing fluoxetine because of the drug's long half-life. In addition, the prolonged duration of CYP450 2D6 inhibition by the moderate CYP450 2D6 inhibitor rolapitant of at least 28 days after its administration should also be taken into account.

References

  1. Silver JM, Yudofsky SC, Kogan M, Katz BL (1986) "Elevation of thioridazine plasma levels by propranolol." Am J Psychiatry, 143, p. 1290-2
  2. Greendyke RM, Kanter DR (1987) "Plasma propranolol levels and their effect on plasma thioridazine and haloperidol concentrations." J Clin Psychopharmacol, 7, p. 178-82
  3. Greendyke RM, Gulya A (1988) "Effect of pindolol administration on serum levels of thioridazine, haloperidol, phenytoin, and phenobarbital." J Clin Psychiatry, 49, p. 105-7
  4. Abernethy DR, Greenblatt DJ, Steel K, Shader RI (1982) "Impairment of hepatic drug oxidation by propoxyphene." Ann Intern Med, 97, p. 223-4
  5. (2001) "Product Information. Prozac (fluoxetine)." Dista Products Company
  6. Fletcher GF, Kazamias TM (1969) "Cardiotoxic effects of Mellaril: conduction disturbances and supraventricular arrhythmias." Am Heart J, 78, p. 135-8
  7. Markowitz JS, Wells BG, Carson WH (1995) "Interactions between antipsychotic and antihypertensive drugs." Ann Pharmacother, 29, p. 603-9
  8. (2001) "Product Information. Mellaril (thioridazine)." Sandoz Pharmaceuticals Corporation
  9. Thomas M, Maconochie JG, Fletcher E (1996) "The dilemma of the prolonged QT interval in early drug studies." Br J Clin Pharmacol, 41, p. 77-81
  10. Hartigan-Go K, Bateman DN, Nyberg G, Martensson E, Thomas SHL (1996) "Concentration-related pharmacodynamic effects of thioridazine and its metabolites in humans." Clin Pharmacol Ther, 60, p. 543-53
  11. Carrillo JA, Ramos SI, Herraiz AG, Llerena A, Agundez JAG, Berecz R, Duran M, Benitez J (1999) "Pharmacokinetic interaction of fluvoxamine and thioridazine in schizophrenic patients." J Clin Psychopharmacol, 19, p. 494-9
  12. Glassman AH, Bigger JT Jr (2001) "Antipsychotic drugs: prolonged QTc interval, torsade de pointes, and sudden death." Am J Psychiatry, 158, p. 1774-82
  13. (2015) "Product Information. Varubi (rolapitant)." Tesaro Inc.
  14. (2019) "Product Information. Thioridazine Hydrochloride (thioridazine)." Mylan Institutional (formerly UDL Laboratories)
View all 14 references

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Drug and food interactions

Moderate

thioridazine food

Applies to: Mellaril-S (thioridazine)

GENERALLY AVOID: Concurrent use of ethanol and phenothiazines may result in additive CNS depression and psychomotor impairment. Also, ethanol may precipitate dystonic reactions in patients who are taking phenothiazines. The two drugs probably act on different sites in the brain, although the exact mechanism of the interaction is not known.

MANAGEMENT: Patients should be advised to avoid alcohol during phenothiazine therapy.

References

  1. Lutz EG (1976) "Neuroleptic-induced akathisia and dystonia triggered by alcohol." JAMA, 236, p. 2422-3
  2. Freed E (1981) "Alcohol-triggered-neuroleptic-induced tremor, rigidity and dystonia." Med J Aust, 2, p. 44-5

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Minor

quiNINE food

Applies to: QM-260 (quinine)

Coadministration with grapefruit juice does not appear to affect the pharmacokinetics of quinine in a clinically relevant manner. Although grapefruit juice is an inhibitor of CYP450 3A4 and quinine is metabolized by this pathway to its major metabolite, 3-hydroxyquinine, a study of ten healthy volunteers found no significant differences in quinine peak plasma concentration (Cmax), time to reach Cmax (Tmax), terminal elimination half-life, systemic exposure (AUC), or apparent oral clearance (Cl/F) when a single 600 mg oral dose of quinine sulfate was administered in combination with 200 mL of orange juice (control), half-strength grapefruit juice, and full-strength grapefruit juice twice daily for 6 days each, separated by a 2-week washout period. Relative to the control period, the apparent renal clearance of quinine was markedly increased by 81% during treatment with half-strength grapefruit juice. However, since renal clearance accounts for approximately 6% of the total clearance of quinine, this change would likely have minimal clinical impact. The lack of a significant interaction is probably due to the fact that grapefruit juice primarily inhibits intestinal rather than hepatic CYP450 3A4, and quinine is not known to undergo significant presystemic metabolism as evidenced by its relatively high oral bioavailability (76% to 88%). Nevertheless, excessive consumption of grapefruit juice and tonic water (which contains quinine) was suspected as the cause of torsade de pointes arrhythmia in a patient with a history of asymptomatic long QT syndrome. Treatment with magnesium sulfate and metoprolol had no effect, but the arrhythmia resolved spontaneously 48 hours after discontinuation of the drinks. Based on current data, moderate grapefruit juice consumption is probably safe for the majority of patients taking quinine.

References

  1. Ho PC, Chalcroft SC, Coville PF, Wanwimolruk S (1999) "Grapefruit juice has no effect on quinine pharmacokinetics." Eur J Clin Pharmacol, 55, p. 393-8
  2. Hermans K, Stockman D, Van den Branden F (2003) "Grapefruit and tonic: a deadly combination in a patient with the long QT syndrome." Am J Med, 114, p. 511-2
  3. (2006) "Product Information. Qualaquin (quinine)." AR Scientific Inc
  4. Zhang H, Coville PF, Walker RJ, Miners JO, Birkett DJ, Wanwimolruk S (1997) "Evidence for involvement of human CYP3A in the 3-hydroxylation of quinine." Br J Clin Pharmacol, 43, p. 245-52
  5. Mirghani RA, Yasar U, Zheng T, et al. (2002) "Enzyme kinetics for the formation of 3-hydroxyquinine and three new metabolites of quinine in vitro; 3-hydroxylation by CYP3A4 is indeed the major metabolic pathway." Drug Metab Dispos, 30, p. 1368-71
View all 5 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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