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Abstract Background Lamivudine (LAM) and tenofovir disoproxil fumarate (TDF) are part of a fixed-dose combination (FDC) therapy recommended by WHO. Both drugs exhibit similar solubility in many solvent systems and tend to have overlapping spectra with maxima at 260 and 270 nm, respectively, in the UV spectrum—thus making their spectrophotometric assay difficult in FDCs. A third-order derivative (D3, d3 A/dλ 3) spectrophotometric technique was applied to simultaneously evaluate TDF and LAM in FDC drugs, with amplitudes at 240 and 262.5 nm, respectively. Pharmacopoeia-recommended chromatographic method was also applied for comparative purpose. Results Method performance by the proposed D3 technique showed linearity for LAM and TDF from 2–10 µg mL−1 to 8–24 µg mL−1, respectively (R 2 ≥ 0.998), while for HPLC method both drugs ranged from 0.25 to 5.0 µg mL−1 (R 2 ≥ 0.999). The intercepts and slopes of the regression equations were ≤ 1.62 × 10−4 and ≤ 3.58 × 10−5, respectively, while calculated standard errors were ≤ 8.04 × 10−5. Limits of detection and quantification for both methods were ≤ 0.46 μg mL−1 and ≤ 1.40 μg mL−1, respectively, for LAM, while corresponding limits for TDF were ≤ 2.61 and ≤ 7.90 μg mL−1. The percentage recovery for both drugs and methods ranged from 94.80 to 100.33%. The amount of LAM and TDF in brands I and II was ≥ 99.59 ± 1.19% and ≥ 99.39 ± 0.63%, respectively, for the proposed D3 spectroscopic method, while corresponding values for the HPLC method were ≥ 99.86 ± 0.50 and ≥ 99.87 ± 0.32%. Statistically, both methods were adjudged to have no significant difference at 95% confidence level as the student’s t-test values; experimental paired t- and F-test values were found satisfactory. Conclusion The D3 spectrophotometric technique was time saving, cheap, simple and more environmental friendly and shows reliability, precision and accuracy and could be used for routine analysis of FDCs where HPLC is not available. Graphical abstract |
