Taking Clindamycin Soon After Finishing Azithromycin

In our latest question and answer, the pharmacist discusses the potential issues of starting clindamycin soon after starting azithromycin,


How long after I finish a round of azithromycin can I start a new round of the antibiotic clindamycin for treatment of strep A? After the first go, the infection did not clear, so a second round (clindamycin) was prescribed.

Asked by Jimmy On Jun 19, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Jun 19, 2022
Last updated Jun 19, 2022

Key points

  • Although they share a similar name, clindamycin and azithromycin are antibiotics in different classes.
  • Clindamycin and azithromycin both work in a similar way, acting on the same bacterial site (50S ribosome). Taking both at the same time will cause them to compete for the same site of action. For this reason, they are generally not used together.
  • There is no defined or recommended waiting period between taking azithromycin and clindamycin. Your doctor may choose to start one right after the other, choose a different antibiotic combination, or monitor your response and adjust your therapy as needed.

Hello, and thanks for your question!

I'm sorry to hear your infection has not cleared up yet. Hopefully, your second round of antibiotics will do the trick.

I do want to mention before getting into the crux of your question, that even though azithromycin and clindamycin have a similar spelling, and share 'mycin' in their name, they are not in the same drug class.

Azithromycin is a 'macrolide' antibiotic and clindamycin is a 'lincosamide' antibiotic. They are similar in how they work but are chemically distinct, and I just wanted to make this distinction.

Can You Use Them Together?

To start off, I want to point out that there is technically no drug interaction between clindamycin and azithromycin.

However, in the vast majority of situations, they should not be used together since they have a similar mechanism of action and actually act on the same site on bacteria.

Specifically, both drugs bind to an area on bacterial ribosomes (known as the 50S subunit), which inhibits protein synthesis, which then in turn stops bacterial replication.

Using them together would cause them to essentially compete for the same site of action.

You won't get an additive benefit when using them together and you would likely be increasing your risk of side effects occurring (I do want to note that some small studies suggest their use together may be beneficial, but this appears to be in only specific situations).

Waiting Period

This brings us to the specific point in your question of how long to wait after finishing azithromycin to take clindamycin.

The main thing we want to consider is how long azithromycin lasts in your system.

Azithromycin has an extremely long half-life for an antibiotic, which is often used as a measure of how long a drug will last in your system (the half-life is technically the time it takes to metabolize 50% of a drug). The half-life of azithromycin is around 40-68 hours,

It generally takes about 5 to 6 half-lives for a drug to be considered completely eliminated from your system, so, for azithromycin, we're talking a week to 10 days after your last dose.

It is because of this long-half life that the drug can be dosed as it is.

Azithromycin can be taken as a single 2-gram dose for many different infections, and the commonly prescribed 5-day 'ZPak' course has antibacterial activity for 10 days, if not longer.

Additionally, many studies show that a once-daily 5-day course of azithromycin is as effective as 10-day courses of the other macrolide antibiotics, like clarithromycin.

I am assuming your doctor has prescribed you clindamycin because your most recent course of azithromycin was ineffective.

Now, there is no defined or guideline-recommended period of time to wait between finishing azithromycin and starting clindamycin.

You could certainly start clindamycin right after azithromycin, but there is a chance the clindamycin won't be fully effective for at least a couple of days due to what I've written about above (that these drugs will compete for the same site of action).

There is also the fact you may be at an increased risk of side effects, like nausea, and diarrhea, since you will have two different antibiotics in your system.

Waiting between taking the two antibiotics has its concerns as well, since you want to treat your infection as soon as possible.

My best advice is to talk to your doctor about what they recommend you do for your specific medical scenario, as these things aren't black and white, and there are many considerations.

I would imagine your doctor will either switch to an antibiotic that doesn't interfere with azithromycin, or they would start you immediately on clindamycin, and monitor you for clinical response (and perhaps lengthen how long you are being treated for).

I say this because you generally err on the side of treating an infection when there are no significant risks of side effects or negative outcomes, and taking clindamycin after azithromycin isn't inherently risky, you just may need to be treated longer with clindamycin or switch to another if you find clindamycin isn't working.

Final Words

The recommended dosing of clindamycin for the treatment of Streptococcus (group A) is 300 mg 3 times daily for 10 days.

You generally start to see some response to your antibiotics within a few days. Be sure to keep in touch with your doctor regarding how you are feeling so they adjust your dose, or drug, as necessary.

Thanks again for your question and for reaching out to us!


  • Azithromycin Monograph, PubChem
  • Clindamycin Monograph, PubChem
  • Combination of Clindamycin and Azithromycin as Alternative Treatment for Toxoplasma gondii Encephalitis, PubMed
  • Different antibiotic treatments for group A streptococcal pharyngitis, PubMed

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at Hello@HelloPharmacist.com! You can also connect with Dr. Brian Staiger on LinkedIn.

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