skip to Main Content

Bactrim Dosage


Bactrim (a combination of two antibiotics: sulfamethoxazole and trimethoprim) is a medication that’s used to treat an expansive list of bacterial infections, such as staph/MRSA. While Bactrim is safely prescribed for patients 2 months of age and older, the dosage needs to be carefully followed to ensure it’s long-term effectiveness for the patients. Below we’ve presented a helpful table for you to cross-reference dosage levels for your patients. Please note that administering Bactrim to newborns or infants younger than 2 months old is not advised due to the risk of serious side effects.

Trimethoprim/sulfamethoxazole Suspension
(40/200 per 5mL)

(must be > 2 months old)

WEIGHT DOSE (Infection*)
(lbs) (kg) (10mg TMP/kg/day)
22 lbs 10 kg 1 tsp PO BID
44 lbs 20 kg 2 tsp BID or 1 tab BID
66 lbs 30 kg 3 tsp BID or 1.5 tab BID
88 lbs 40 kg 4 tsp BID or 2 tab BID or 1 DS tab BID
Adult (skin infection; MRSA) 1 DS tab PO BID ** (others will give 2 DS tab PO BID to obese patients)

*doses are for acute otitis media or UTI
**reference: personal communication with Dirk Elston, MD
(1 tsp = 1 teaspoon = 5mL)
(TMP = trimethoprim)
1 tab = 80/400 (= 2 tsp of the suspension)
1 DS tab = 160/800 (= 4 tsp of the suspension)


High Dose Bactrim for treating PCP (as a point of reference)

WEIGHT DOSE – Every 6 Hours (= 20mg TMP/kg/day dose)
(lbs) (kg) Teaspoonfuls Tablets
18 lbs 8 kg 1 (5 mL)
35 lbs 16 kg 2 (10 mL) 1
53 lbs 24 kg 3 (15 mL) 1 1/2
70 lbs 32 kg 4 (20 mL) 2 (or 1 DS Tablet)
88 lbs 40 kg 5 (25 mL) 2 1/2
106 lbs 48 kg 6 (30 mL) 3 (or 1 1/2 DS Tablets)
141 lbs 64 kg 8 (40 mL) 4 (or 2 DS Tablets)
176 lbs 80 kg 10 (50 mL) 5 (or 2 1/2 DS Tablets)

For the lower limit dose (15 mg/kg trimethoprim and 75 mg/kg sulfamethoxazole per 24 hours) administer 75% of the dose in the above table.

Disclaimer: All of the information on this website is being presented as helpful reference material but should not be considered authoritative. There are no references because the information has been collected over the years piecemeal from notes, lectures, journals, textbooks, personal communications with other physicians and experience. You may disagree with some of it. Take it simply for what it is: information that I have found useful in my day to day practice as a clinical dermatologist and my hope is that you find it useful as well.


4060 Sheridan Street, Suite C
Hollywood, Florida 33021

From the moment I walked into his office, I was impressed by the warm and welcoming environment. The staff was friendly and accommodating, and the doctor was incredibly knowledgeable and attentive.
J. Michaels
Rating 5/5
And read more of our 1,500+ reviews on Google.

We are a member of the TopLine MD Alliance, a collective group of practices, providers and specialty centers that help patients navigate a complicated healthcare system. Membership in the alliance is highly selective and based on exceptional patient satisfaction. Our priority is to provide you with top-of-the-line care, through a network of dedicated people you can trust, while making your experience simple and convenient.

Florida Academy of Dermatology

© 2023 MINARS DERMATOLOGY. All rights reserved.

Back To Top