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This thesis describes bioanalytical methods for drug determination in biological matrixes, with drugs in focus used against diseases largely affecting low-income countries. Solid-phase extraction is used for sample cleanup, and processed samples are analyzed by liquid chromatography. Developed bioanalytical methods are validated according to international guidelines. Eflornithine (DFMO) is a chiral drug, used for treating human African trypanosomiasis. A bioanalytical method for determination of DFMO enantiomers in plasma is presented. The enantiomers are detected by evaporative light-scattering detection. The method has been applied to determination of D-DFMO and L-DFMO in rats, after intravenous and oral administration of racemic DFMO. It is concluded that DFMO exhibits enantioselective absorption, with the more potent enantiomer L-DFMO being less favored. Sulfadoxine (SD) and sulfamethoxazole (SM) are sulfa-drugs used for malaria and pneumonia respectively. Two methods are described for simultaneous determination of SD and SM in capillary blood sampled on filter paper. The former method allows direct injection of extracts from dried blood spots (DBS), while for the latter method solid-phase extraction is added. Pre-analytical factors contributing to measurement uncertainty is also discussed, and it is concluded that it is of high importance that homogeneity in type of sampling paper and sampling volume is assured. Piperaquine (PQ) is an antimalarial, increasingly used in artemisinin combination therapy. A method for determination of piperaquine in DBS is presented. By using a monolithic LC column, a very short LC analysis of two minutes per sample is achieved. A method for simultaneous determination of three antiretroviral drugs i.e. lamivudine (3TC), zidovudine (AZT) and nevirapine (NVP), in DBS samples is described. The method is applied to drug determination in two subjects after receiving standard antiretroviral treatment. Conclusion is that the method is suitable for determination of 3TC and NVP, and to some extent for AZT.