Answer

Dextromethorphan, the cough suppressant in both DayQuil and NyQuil, is safe to take with the Z-Pack (azithromycin) and Tamiflu (oseltamivir). There are no known drug interactions.

For your situation, unless you have a contraindication to dextromethorphan, or your doctor has recommended against it, it is considered safe to use with either DayQuil or NyQuil.

Remember that NyQuil and DayQuil are combination ingredient products, and contain many of the same drugs. Therefore, you don't want to use them at the same time. Be sure to separate doses by at least 6 hours.

DayQuil contains the following ingredients:

  • Acetaminophen 325 mg
  • Dextromethorphan HBr 10 mg
  • Phenylephrine 5 mg
  • Guaifenesin 200 mg (only in DayQuil Severe)

NyQuil contains the following ingredients:

  • Acetaminophen 325 mg
  • Dextromethorphan HBr 15 mg
  • Doxylamine succinate 6.25 mg
  • Phenylephrine 10 mg (Only in NyQuil Severe)

Tamiflu is safe to take with most drugs, as it has few documented interactions. In fact, only two are well known:

  • Intranasal Influenza Vaccine: (Major)
  • Probenacid

Giving Tamiflu with a live flu vaccine (such as the intranasal one) may inhibit viral replication and reduce vaccine efficacy.

Co-administering probenacid and Tamiflu can raise Tamiflu concentrations in the body nearly two-fold. However, the prescribing information for Tamiflu states that the interaction is not clinically relevant, due to the safety margin of the drug and no dosage adjustment is needed.

The Z-Pack has far more interactions than Tamiflu, but is safe with dextromethorphan (and all the other ingredients in NyQuil/DayQuil).

As mentioned above, taking a cough suppressant should be fine with the medications you mentioned. If you have further questions, be sure to send us an email or leave a comment below so we can reply.


Summary

There is no known interaction between dextromethorphan, azithromycin and Tamiflu.

References
  1. Tamiflu Prescribing Information. Genetech
  2. Azithromycin Prescribing Information. PubMed
  3. DrugBank Interaction Checker (PharmacistAnswers). Interaction Checker