Lapis ISSN 2398-2969

Trimethoprim/sulfamethoxazole

Synonym(s): Trimethoprim and sulfamethoxazole, TMP/SMX, Co-trimoxazole

Contributor(s): Joanna Hedley, Vicki Baldrey

Introduction

Name

  • Trimethoprim/sulfamethoxazole.

Class of drug

  • Potentiated sulfonamide antimicrobial.

Description

Molecular formula

  • C24H29N7O6S.

Molecular weight

  • 543.599 g/mol.

Storage requirements

  • Protect from light and store at room temperature (<25°C/77°F).

Uses

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Indications

  • Useful in the management of many infections, especially those affecting the respiratory tract, urinary tract or prostate.
  • Effective against a range of Gram-positive and Gram-negative bacteria, including Streptococcus Streptococcus spp, Enterobacteriaceae, Brucella and Nocardia. Also effective against Pneumocystis carinii, Toxoplasma gondii Toxoplasma gondii and coccidia.
  • Pseudomonas Pseudomonads and Leptospira are usually resistant.
  • Trimethoprim/sulfonamides are ineffective in the presence of necrotic tissue.

Administration

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Pharmacokinetics

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Precautions

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Interactions

With other drugs

  • Warfarin - concurrent use may enhance the anticoagulant effect of warfarin.
  • Antacids - bioavailability of trimethoprim/sulfamethoxazole may be reduced.
  • Drugs containing procaine - the action of sulfonamides may be inhibited as procaine is a precursor for para-aminobenzoic acid.
  • Urinary acidifying agents - concurrent use may increase the risk of sulfonamide crystallization within the urinary tract.
  • Theoretically other plasma protein-bound drugs (such as thiazide diuretics) could be displaced by concurrent administration of trimethoprim/sulfamethoxazole, although the clinical relevance of this is unknown.

With diagnostic tests

  • May result in false-positive measurements of urine glucose if using the Benedict’s method.
  • May reduce Schirmer II tear test results.

Adverse Reactions

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Shirani D, Selk Ghaffari M, Akbarein H et al (2010) Effects of short-term oral administration of trimethoprim-sulfamethoxazole on Schirmer II tear test results in clinically normal rabbits. Vet Rec 166 (20), 623-624 PubMed.

Other sources of information

  • Meredith A (2015) BSAVA Small Animal Formulary. Part B: Exotic Pets. 9th edn. BSAVA, Quedgeley, Gloucester.

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