SALIVARY, PROTEIN UNBOUND AND TOTAL PLASMA CONC OF RIFAMPICIN HADIJA H SEMVUA 11/12/2015KCRI_PhD SYMPOSIUM

Outline Background information Study objectives Methodology Results Discussion and conclusion Acknowledgement 11/12/2015KCRI_PhD SYMPOSIUM

Background information Development of new drugs, evaluation of drug-interactions and therapeutic drug monitoring in individual patients require pharmacokinetic analysis Pharmacokinetic sampling enables an accurate assessment of the total exposure of the drugs. Saliva may be an easily obtainable alternative sampling matrix for PK studies. salivary concentrations reflect the protein-unbound (active) fraction of rifampicin in plasma. 11/12/ KCRI_PhD SYMPOSIUM 2013

Study objectives To compare the PK of rifampicin in saliva and plasma To assess whether saliva could be an alternative matrix for PK studies and TDM for rifampicin. 11/12/ KCRI_PhD SYMPOSIUM 2013

Methodology Intensive pharmacokinetic sampling for INH, RIF, ETH and PZA Time-matched samples of saliva and plasma Samples were taken at (t=0) and 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours. Plasma concentrations were quantified using validated HPLC assays Pharmacokinetic parameters were determined using WinNonlin Programme (version 5.2) All statistical analyses were done in SPSS, version /12/ KCRI_PhD SYMPOSIUM 2013

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Analysis Salivary, total (protein-unbound plus bound) and unbound plasma concentrations of rifampicin were measured. Performance of salivary concentrations to predict plasma concentrations was evaluated. 11/12/2015KCRI_PhD SYMPOSIUM

Results The geometric mean AUC 0-24h of rifampicin in saliva was 3.1 h*mg/L. Protein-unbound AUC 0-24h in plasma was 5.3 h*mg/L AUC 0-24h based on total concentrations (bound and unbound was 32.7 h*mg/L. Corresponding geometric mean C max values were 0.64, 1.0 and 6.8 mg/L respectively. 11/12/2015KCRI_PhD SYMPOSIUM

Pharmacokinetic of rifampicin in saliva and plasma (N= 15) 11/12/2015KCRI_PhD SYMPOSIUM

Results cont The prediction of total and unbound plasma concentrations based on salivary concentrations of rifampicin resulted in median percentage prediction errors (MPPE) of 13.4% and 6.0% Measure of accuracy (<15%) Median absolute percentage prediction errors (MAPE) was again 35.7% and 23.0%, respectively. Measure of precise (>15%). 11/12/2015KCRI_PhD SYMPOSIUM

Discussion The salivary AUC 0-24h and C max of rifampicin were much lower than those in plasma This was anticipated, as only the protein-unbound (free) fraction of a drug in plasma can pass into the salivary compartment. Several other factors that (apart from protein binding) determine the extent of diffusion of drugs into saliva, including lipid solubility, the degree of ionisation in blood and in saliva, and salivary flow The average protein binding of 84% which was found in this study is close to 80% protein binding for rifampicin (Acocela G 1978, Holdiness 1984). 11/12/2015KCRI_PhD SYMPOSIUM

Discussion cont The rifampicin molecule exhibits high lipid solubility [Kenny 1981] ; its degree of ionisation is dependent on the pH of the solution in which it resides. The rapid appearance of rifampicin in saliva suggest that this TB drug enters saliva by passive diffusion instead of active transport. 11/12/2015KCRI_PhD SYMPOSIUM

Disc cont. Kenny and Strates 1981 stated that highest rifampicin levels in saliva and sputum are obtained up to 4hr. Gurumuthy et al 1990 showed that peak concentrations of rifampicin in saliva were 10.6% of those in plasma. Very similar to data from our study (0.64mg/L to 6.8mg/L) Orisakwe et al 2004 found a much higher saliva to plasma ratio for AUC 0-24h (i.e. a ratio of 0.67). In our study it was However in their study they used chewing gum stimulated saliva and intensive pharmacokinetic sampling in healthy volunteers. 11/12/2015KCRI_PhD SYMPOSIUM

Conclusion The AUC 0-24h of rifampicin in saliva was significantly lower than the protein-unbound plasma AUC 0-24h. Due to inadequate precision associated with this study prediction, we can not advocate on the the use of saliva as alternative matrix for TDM 11/12/2015KCRI_PhD SYMPOSIUM

Acknowledgement  Sponsoring programme: APRIORI  Kilimanjaro Clinical Research Institute  Kibong’oto National TB Hospital (TZ)  Radboud University Nijmegen Medical Centre (NL)  Department of pharmacy Radboud University (NL)  Supervisors and TB team members of KCRI/KNTH 11/12/ KCRI_PhD SYMPOSIUM 2013

Ahsanteni sana 11/12/2015KCRI_PhD SYMPOSIUM