title: Spectrophotometric determination of sulphamethoxazole and trimethoprim (co-trimoxazole) in binary mixtures and in tablets.
abstract: BACKGROUND
  The formulation of sulphamethoxazole (S) and trimethoprin (T) (CO-TRIMOXAZOLE) in a combination mixture is very good pharmacologically since it enhances the efficacy of the individual drugs. However in this combination, difficulties in analysis on ordinary UV spectrophotometry are introduced because the two components give overlapping spectral bands on zero-order. The United States Pharmacopoea (USP)-recommended HPLC analytical method is quite expensive.
  
  
  OBJECTIVE
  The objective of the present work was to assess whether derivative spectrophotometry could be used to circumvent the overlapping spectral bands of the components and hence use it for routine analysis of the drug.
  
  
  METHODS
  Experimental.
  
  
  METHODS
  The aqueous solution of the individual drugs and their binary mixtures were scanned on zero order and on first derivative at the wave length between 200- 300 nm and at the pH of 4.5.
  
  
  RESULTS
  The zero-order spectra of the compounds were completely overlapping. However the first-derivative scan offered better separation and hence T was determined from the absorbance at 237.6 nm with negligible contribution from S (since at this point it was reading zero). Likewise S was determined at a wavelength of 259 nm when T was reading zero. The linear calibration graphs were obtained for 4-25 microg x ml(-1) of S and for 4-20 microg x ml(-1) of T.
  
  
  CONCLUSIONS
  The method is rapid, simple and can be applied successfully to assay a mixture of the two drugs in pharmaceutical preparations.
authors.affiliation: Department of Pharmacy, Makerere University, Faculty of Medicine, PO Box 7072, Kampala, Uganda. shurik@swiftuganda.com
authors.forename: S
authors.initials: S
authors.lastname: Balyejjusa
authors.forename: R O
authors.initials: RO
authors.lastname: Adome
authors.forename: D
authors.initials: D
authors.lastname: Musoke
mesh_terms: D015203:Reproducibility of Results; D012996:Solutions; D013053:Spectrophotometry; D013607:Tablets; D013678:Technology, Pharmaceutical / Q000379:methods*; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000737:chemistry*
chemical_list: D012996:Solutions; D013607:Tablets; D015662:Trimethoprim, Sulfamethoxazole Drug Combination