# Presentation: 132538

## Liposome Drug Products: Bioavailability and Bioequivalence Issues

- Kofi A. Kumi, R.Ph., Ph.D.
- Office of Clinical Pharmacology and Biopharmaceutics
- Division of Pharmaceutical Evaluation III
- ACPS 7/20/2001

## Bioavailability  

- Regulatory Definition (21 CFR 320.1(a)): “Bioavailability means the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action.”

## Bioequivalence 

- Regulatory Definition (21 CFR 320.1(e)):“Bioequivalence means the absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study....”

## Bioavailability/Bioequivalence

- Key factors for consideration in assessing bioavailability (BA) and bioequivalence (BE) of liposome drug products
- Release of active moiety from drug product
- Availability at the site of action

## Types of Evidence to EstablishBA/BE

- 			           * ****21 CFR 320.24***The following *in vivo* and *in vitro* approaches, in *descending order of accuracy, sensitivity, and reproducibility*, are acceptable for determining the bioavailability or bioequivalence of a drug product:
- Blood/plasma/serum drug conc. measurement in humans
- Urinary excretion in humans
*In vivo* pharmacological effect
- Well-controlled clinical trials
*In-vitro* test
- Any other approach deemed adequate by FDA

## Prerequisites for Using PK Method to Assess BA/BE

-  Availability of a specific and sensitive analytical method useful when determining *in vivo* release of drug from liposomes
-  Rate of release of drug from carrier affects overall pharmacokinetics (PK) of drug and carrier
-  Demonstrating* in vivo* stability (Pilot)
-  Separate measurement of encapsulated (E) & unencapsulated (U) drug in an *in vivo single dose* study. If the drug remains in the circulation substantially in the E form and the ratio of U/E remains constant, then the liposome drug product may be considered stable in vivo.

## Classification of Liposome Drug Products Based on MPS

-  Mononuclear Phagocyte System (MPS)
-     = Reticuloendothelial system (RES)
-  MPS Uptake
-  MPS Avoidance
-  Intermediate

## MPS Uptake Liposomes

- Preferential uptake (targeted) by MPS
- Relatively short duration in systemic circulation
- Generally, active drug slowly released back into systemic circulation from depot site (MPS)
- PK dose-dependent
- PK affected by particle size, charge, etc.

## MPS Avoidance Liposomes

- Designed to evade recognition and uptake by MPS
- Remain in systemic circulation for extended period
- Preferential uptake (“targeting”) at  site(s) other than MPS
- PK dose-independent
- PK affected by liposome composition, charge, etc.

##    The Key Issues

-  Is blood/plasma/serum concentration of drug adequate to determine BA and BE in view of the fact that
- Liposome drug products (LDP) may or may not be stable *in vivo*
- The residence time of the LDP in the blood/ serum/plasma may differ
- Different LDPs may be designed targeted toseparate sites
- e.g. MPS, Tumor cells

## MPS Uptake: Suggested Scheme for BA/BE Determination

## MPS Avoidance: Suggested Scheme for  BA/BE Determination

## Combined Scheme for                     Determination of BA/BE

## Acknowledgements

- Mei-Ling Chen		Helen Winkle
- Barbara Davit		Ajaz Hussain
- Arthur Shaw			Yuan Yuan Chiu
- Liposome WG members	Larry Lesko
- 			                   John Lazor
- 					Arzu Selen
- 					Funmi Ajayi
- 					Mehul Mehta
- 					Hae-Young Ahn
- 					CDS CC members
- 					DPEIII colleagues