- Pharmacokinetics (PK) is the study of the transit of drug into, within and removal from the body to reveal how the body acts on a drug when it is taken. There are four major areas in PK: absorption, distribution, metabolism and elimination. Pharmacokinetics research can be separated into two areas: clinical research and analysis of pharmacokinetics values. Upon obtaining drug concentrations at each sample time point, computer analysis using pharmacokinetics software is performed to determine the pharmacokinetics values of the drug: T[subscript max] (time to peak drug plasma concentration), C[subscript max] (peak plasma drug concentration), V (volume of distribution), half-life (t1/2), elimination constant (k) etc. Current pharmacokinetic software on the market includes programs such as WinNonlin, Kinetica, Pharmod, NONMEM. In this thesis, WinNonlin and Kinetica are used to analyze plasma drug concentrations versus time data sets to compare and validate the results of both software packages. There are two drug models used in this study, xanthohumol and lipoic acid. Xanthohumol (XN) is the most common flavonoid component found in hops, totaling about 82-89% of the amount of prenylated flavonoids present. However, there are other prenylflavonoids, isoxanthohumol (IX) and 8-prenylnaringenin (8PN). Isoxanthohumol (IX) can occur during the brewing process. The content of xanthohumol and isoxanthohumol depends on brewing conditions. 8-prenylnaringenin is produced by O-demethylation of isoxanthohumol. In this study xanthohumol was given in 20, 60 or 80 mg doses to healthy volunteers. After xanthohumol administration the plasma concentrations of xanthohumol increased rapidly with all three doses and reached the peak concentrations in 0.78, 1.23 and 2.03 hours for 20, 60 and 180 gm dose of xanthohumol, respectively. Xanthohumol and its metabolites were eliminated in 1, 2 or 3 days. Moreover there was linearity in the pharmacokinetics of xanthohumol as shown in the C[subscript max] versus dose curve, R² is 1. Isoxanthohumol was also formed rapidly from xanthohumol. T[subscript max] are 7 and 5 hours for medium and high dose respectively. Xanthohumol and isoxanthohumol each have a high volume distribution. Unfortunately, no results for 8-prenylnaringenin (8PN) were obtained due to plasma drug concentrations being undetectable in all subjects. Lipoic acid (LA) is also known as alpha lipoic acid or thioctic acid. It has two enantiomers, (R)-(+)-lipoic acid (RLA) and (S)-(-)-lipoic acid (SLA). A racemic mixture (R/S)-lipoic acid (R/S-LA) is commercially available. R-form of lipoic acid occurs naturally in food but the synthetic product is a racemic mixture. Lipoic 500mg in R- and racemic forms were given to healthy volunteers. Lipoic acid is absorbed rapidly in both forms, 40 minutes for racemic form and 30 minutes for R-form. The C[subscript max] and AUC values of racemic form are comparable to the R-form, around 2400 ng/mL for Cmax and 115,000 min*(ng/mL) for AUC. Comparing the results obtained on the pharmacokinetic parameters from the two pharmacokinetic software, Kinetica and WinNonlin revealed that almost all pharmacokinetic parameters of xanthohumol and isoxanthohumol obtained from Kinetica and WinNonlin are the same. However for the pharmacokinetic parameters of lipoic acid, all parameters are different, p-value <0.05, except for C[subscript max] and T[subscript max]. The comparisons of pharmacokinetic parameters show that only the normal data set of xanthohumol and isoxanthohumol produced the same results from Kinetica and WinNonlin software programs. The pharmacokinetic results obtained from pharmacokinetic programs vary due to the different methods of calculation and variations and limitations of the two programs.