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Drug Interactions between Dolophine and fosamprenavir

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

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Interactions between your drugs

Moderate

methadone fosamprenavir

Applies to: Dolophine (methadone) and fosamprenavir

MONITOR: Coadministration with fosamprenavir alone or in combination with low-dose ritonavir may decrease the plasma concentrations of methadone. The exact mechanism of interaction has not been described. In 16 study subjects treated with methadone (44 to 100 mg daily for at least 30 days) and amprenavir (1200 mg twice a day for 10 days), mean peak plasma concentration (Cmax), systemic exposure (AUC) and trough plasma concentration (Cmin) of the pharmacologically active R(+) enantiomer of methadone were reduced by 25%, 13% and 21%, respectively, compared to administration of methadone alone. Similarly, in 19 study subjects administered methadone (70 mg to 120 mg once a day) in combination with fosamprenavir/ritonavir (700 mg/100 mg twice a day) for two weeks, Cmax, AUC and Cmin of R(+) methadone decreased by 21%, 18% and 11%, respectively.

GENERALLY AVOID: Methadone may decrease the plasma concentrations of amprenavir in the absence of low-dose ritonavir as a pharmacokinetic booster. In 16 study subjects treated with methadone (44 to 100 mg daily for at least 30 days) and amprenavir (1200 mg twice a day for 10 days), mean serum amprenavir Cmax, AUC and Cmin were reduced by 27%, 30% and 25%, respectively, compared to a non-matched historical control group. The clinical significance of these changes is unknown. In contrast, the pharmacokinetics of amprenavir administered as fosamprenavir/ritonavir were not altered by methadone when compared to historical control data.

MANAGEMENT: Based on available pharmacokinetic data, the interaction between methadone and fosamprenavir/ritonavir is not expected to be clinically significant. However, as a precaution, patients should be monitored for opiate withdrawal symptoms if prescribed fosamprenavir/ritonavir while receiving methadone treatment. Patients should be advised to notify their caregiver if they experience symptoms of methadone withdrawal such as restlessness, insomnia, sweating, lacrimation, or rhinorrhea. Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiretroviral drug levels, fosamprenavir should preferably not be used with methadone in the absence of ritonavir as a pharmacokinetic booster.

References

  1. (2003) "Product Information. Lexiva (fosamprenavir)." GlaxoSmithKline

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Drug and food interactions

Moderate

methadone food

Applies to: Dolophine (methadone)

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of methadone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In 8 study subjects stabilized on methadone maintenance treatment, ingestion of regular strength grapefruit juice (200 mL one-half hour before and 200 mL simultaneously with the daily methadone dose) for five days resulted in an approximately 17% mean increase in methadone peak plasma concentration (Cmax) and systemic exposure (AUC) and a 14% mean decrease in apparent clearance for both the R(+) and S(-) enantiomers. Grapefruit juice did not affect the time to peak level (Tmax), terminal half-life, or apparent volume of distribution of methadone. No signs or symptoms of methadone toxicity or changes in intensity of withdrawal symptoms were reported in the study.

MANAGEMENT: Given the interindividual variability in the pharmacokinetics of methadone, a more significant interaction with grapefruit juice in certain patients cannot be ruled out. Patients treated with methadone should preferably avoid or limit the consumption of grapefruit juice, particularly during the induction of maintenance treatment.

References

  1. Iribarne C, Berthou F, Baird S, Dreano Y, Picart D, Bail JP, Beaune P, Menez JF (1996) "Involvement of cytochrome P450 3A4 enzyme in the N-demethylation of methadone in human liver microsomes." Chem Res Toxicol, 9, p. 365-73
  2. Oda Y, Kharasch ED (2001) "Metabolism of methadone and levo-alpha-acetylmethadol (LAAM) by human intestinal cytochrome P450 3A4 (CYP3A4): potential contribution of intestinal metabolism to presystemic clearance and bioactivation." J Pharmacol Exp Ther, 298, p. 1021-32
  3. Benmebarek M, Devaud C, Gex-Fabry M, et al. (2004) "Effects of grapefruit juice on the pharmacokinetics of the enantiomers of methadone." Clin Pharmacol Ther, 76, p. 55-63
  4. Foster DJ, Somogyi AA, Bochner F (1999) "Methadone N-demethylation in human liver microsomes: lack of stereoselectivity and involvement of CYP3A4." Br J Clin Pharmacol, 47, p. 403-12
View all 4 references

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Moderate

fosamprenavir food

Applies to: fosamprenavir

ADJUST DOSING INTERVAL: Food may reduce the systemic bioavailability of amprenavir from fosamprenavir oral suspension. The mechanism of interaction has not been described. According to the product labeling, administration of fosamprenavir oral suspension (1400 mg single dose) with a high-fat meal (967 kcal, 67 g fat, 33 g protein, 58 g carbohydrate) reduced amprenavir peak plasma concentration (Cmax) by 46% and systemic exposure (AUC) by 28% compared to administration in a fasted state. The time to reach peak plasma level (Tmax) was delayed by 0.72 hours. In contrast, the same high-fat meal did not affect the pharmacokinetics of amprenavir from fosamprenavir tablets.

MANAGEMENT: Fosamprenavir suspension should be administered on an empty stomach in adults, but with food in pediatric patients to aid palatability and compliance. If emesis occurs within 30 minutes after dosing the suspension, the dose should be repeated. Fosamprenavir tablets may be taken with or without food.

References

  1. (2003) "Product Information. Lexiva (fosamprenavir)." GlaxoSmithKline

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Moderate

methadone food

Applies to: Dolophine (methadone)

GENERALLY AVOID: Ethanol may potentiate the central nervous system (CNS) depressant effects of opioid analgesics. Concomitant use may result in additive CNS depression and impairment of judgment, thinking, and psychomotor skills. In more severe cases, hypotension, respiratory depression, profound sedation, coma, or even death may occur.

MANAGEMENT: Concomitant use of opioid analgesics with ethanol should be avoided.

References

  1. Linnoila M, Hakkinen S (1974) "Effects of diazepam and codeine, alone and in combination with alcohol, on simulated driving." Clin Pharmacol Ther, 15, p. 368-73
  2. Sturner WQ, Garriott JC (1973) "Deaths involving propoxyphene: a study of 41 cases over a two-year period." JAMA, 223, p. 1125-30
  3. Girre C, Hirschhorn M, Bertaux L, et al. (1991) "Enhancement of propoxyphene bioavailability by ethanol: relation to psychomotor and cognitive function in healthy volunteers." Eur J Clin Pharmacol, 41, p. 147-52
  4. Levine B, Saady J, Fierro M, Valentour J (1984) "A hydromorphone and ethanol fatality." J Forensic Sci, 29, p. 655-9
  5. Sellers EM, Hamilton CA, Kaplan HL, Degani NC, Foltz RL (1985) "Pharmacokinetic interaction of propoxyphene with ethanol." Br J Clin Pharmacol, 19, p. 398-401
  6. Carson DJ (1977) "Fatal dextropropoxyphene poisoning in Northern Ireland. Review of 30 cases." Lancet, 1, p. 894-7
  7. Rosser WW (1980) "The interaction of propoxyphene with other drugs." Can Med Assoc J, 122, p. 149-50
  8. Edwards C, Gard PR, Handley SL, Hunter M, Whittington RM (1982) "Distalgesic and ethanol-impaired function." Lancet, 2, p. 384
  9. Kiplinger GF, Sokol G, Rodda BE (1974) "Effect of combined alcohol and propoxyphene on human performance." Arch Int Pharmacodyn Ther, 212, p. 175-80
View all 9 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.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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