How Long To Wait Before Sun Exposure After Taking Bactrim

In our latest question and answer, the pharmacist discusses how long you need to wait after taking Bactrim (sulfamethoxazole/trimethoprim) to go in the sun.

Question

How many days after finishing Bactrim do I need to wait before sun exposure?

Asked by Cindy On Jun 19, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Jun 19, 2022
Last updated Jun 19, 2022

Key points

  • Bactrim can increase sensitivity to sunlight, making you more susceptible to sunburns.
  • Bactrim is completely metabolized and eliminated from your system in about 3 days, and your sensitivity to the sun should be back to normal after that time.

Hello and thank you for reaching out!

Overview

Bactrim, also known as co-trimoxazole, is a combination antibiotic, consisting of sulfamethoxazole and trimethoprim, that is used to treat a variety of bacterial infections. 

Bactrim, like many other drugs, can increase an individual's sensitivity to the sun.

This sensitivity to sun exposure is actually considered a phototoxic reaction, where the drug (Bactrim in this case) absorbs UVA light and causes cellular damage.

This reaction can occur when exposed to sufficient amounts of and is often characterized as an exaggerated sunburn.

This reaction can occur within minutes after the sun exposure. In most cases, the affected areas are only those that are directly exposed to sunlight.

The best way to avoid this reaction from happening is to avoid prolonged sun exposure while taking the drug or using a broad-spectrum sunscreen.

How Long To Wait

In terms of how long to avoid direct sun, you have to consider how long it takes for Bactrim to be metabolized and removed from your system.

The half-life of a drug is a good way to estimate how long it takes for it to be eliminated (the half-life of Bactrim is between 8-10 hours).

It takes 5 to 6 half-lives, in general, to eliminate a drug from your system. Therefore, the Bactrim should be eliminated from your system after about three days.

To ensure that you do not have a phototoxic reaction to the sun, you should wait 3 days until direct sunlight exposure to be completely safe.  At the very least, remember to practice safe sun protection any time you are in the sun.

It is recommended by the CDC to use a sunscreen 15 SPF or higher anytime you are in the sun to reduce the risk of skin cancer and reapply after 2 hours.

If you are going to be in the sun for a long period of time, attempt to cover up as much as possible with long sleeves and pants, wear a hat, and protect your eyes from cataracts with sunglasses.

Final Words

Thanks again for your question and feel free to reach out anytime!

References

  • Bactrim Prescribing Information, AccessFDA
  • Bactrim Monograph, PubChem
  • Drug-induced photosensitivity: new insights into pathomechanisms and clinical variation through basic and applied science, PubMed

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 11 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication related questions!

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