DISSOLUTION & ABSORPTION
2020 Anna Řezáčová
DISSOLUTION & ABSORPTION
Interaction active ingredient × organism
➢ pharmaceutical phase – disintegration, dissolution
(pharmaceutical availability)
➢ pharmacokinetic phase – ADME (biological availability),
AUC, cmax, tmax
➢ pharmacodynamic phase – interaction between drug and receptor
(therapeutic effect)
oral administration
disintegration
dissolution
ingredient can diffuse
absorption
hepatic pass
systemic distribution
resorption part
first pass effect
Bioavailability
galenic
availability
time
bloodconcentration
characterize a ratio between solubility in water and lipids
permeability across membranes
Bioavailability
Permeability
high
Class 1
(amphiphilic)
tramadol.HCl
losartan
pravastatin
Class 2
(lipophilic)
atorvastatin
itraconazole
valsartan
Permeability
low
Class 3
(hydrophilic)
gabapentin
metformin.HCl
valcyclovir
Class 4
(trouble makers!)
acyclovir
furosemide
cyclosporine
Solubility
high
Solubility
low
➢ highly soluble API (BCS) – its highest dose is soluble in 250 ml
of a dissolution medium in physiological pH range
➢ highly permeable API (BCS)
– absorption is > 90%
Biopharmaceutical Classification System (BCS)
BCS
class
Solubility Permeability Speed
limiting item
Dissolution
requirements
Note
1 high high stomach
emptying
fast
in all pH range (85%
in 30 min
in all media)
2 low high dissolution specification based
on IVIVC
absorption
controlled by
solubility of API
3 high low absorption
through
instestine
membrane
very fast
in all pH range (85%
in 30 min
in all media)
fast solubility
required to
maximize the
absorption
4 low low dissolution
and absorption
low chance
for IVIVC
prodrug
preparation,
higher solubility
= higher
permeability
Biopharmaceutical Classification System (BCS)
➢ disintegration – ability of a dosage form to disintegrate
into particles (compression pressure, porosity,
excipients)
➢ dissolution – releasing of molecules (ions) from a crystal
bond and their diffusion in a solvent or digestive
juices (chemical form: salt, weak acid, weak base;
physical form: amorphous, polymorph, particle size)
Disintegration × dissolution
➢ disintegration – studies
if tablets or capsules
disintegrate under defined
experimental conditions
in a defined liquid, within
defined time
Disintegration
➢ process, by which a solid substance comes into a solvent and
becomes a solution
➢ necessary requirement for drug absorption
➢ important tool for proposal, manufacture, evaluation and
quality control of dosage forms
➢ connection of in vitro testing and in vivo availability
Dissolution
dn/dt – a mass of a tested substance
dissolved per time unit
D – diffusion coefficient
S – area of phase boundary between
a solid phase and a solution
cS – concentration of a saturated
solution on a phase boundary
c – concentration in all volume
δ – width of diffusion layer
➢ Noyes-Whitney equation
Dissolution of API – Intrinsic dissolution
➢ pure API or a mixture with excipients
➢ critical parameter – preparation (compression of a tablet)
Dissolution of API – Intrinsic dissolution
MODIFICATION OF API SOLUBILITY
Dissolution
modifying factors
Physicochemical
properties of API
Physiological factors
in GIT
diffusion coefficient D molecule size Mr, temperature viscosity of digestive
juices
surface area S particle size, wettability surfactants, bile
width of diffusion layer δ ––– motility, flow rate
solubility cS hydrophilicity, crystal structure,
solubilisation
pH in GIT, bile, food,
buffer capacity
Dissolution profile
0
20
40
60
80
100
0 10 20 30 40 50 60
time (min)
dissolvedamount
(%)
➢ dissolution profile is a dependence of released amount
of active substance on time
➢ specification of dissolution is specified by minimal
acceptable amount of released active substance
within specified time (minimal XX % within YY min)
Dissolution – Dissolution profile, specification
➢ physicochemical properties of API (solubility, polymorphy,
size and shape of particles, porosity)
➢ formulation components (excipients, buffers, surfactants)
➢ manufacturing process (mixing process, wet granulation,
melt extrusion, tableting pressure)
➢ physical properties of a dosage form (wettability, swelling,
disintegration)
Rate of active substance releasing
from a dosage form
➢ dissolution test
▪ media composition, pH, ion power, buffer capacity
▪ media volume
▪ stirring (hydrodynamics)
Rate of active substance releasing
from a dosage form
➢ temperature: (37 ± 0.5) °C
➢ buffer pH: 1 to 6.8 (± 0.05)
➢ volume: 500 – 1000 ml
▪ saturated concentration determination, sink conditions
calculation cS/cd > 3
➢ additives: surfactants, enzymes
➢ rotation speed: 50 – 100 rpm
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
dissolvedamountin%
time in minutes
water 0.1 M HCl 0.01 M HCl phosphate buffer pH 6.8
Dissolution media
➢ 7 types according to the USP
▪ baskets
▪ paddles
▪ reciprocating cylinder
▪ flow-through cell
▪ paddle over disk
▪ rotating cylinder
▪ reciprocating holder
▪ special instruments (TNO TIM-1, „Golem“)
▪ on-line
▪ off-line
Dissolution methods
➢ 1 – basket, 2 – paddle
➢ limitation – traditional closed models, dissolved drug stays
in the system – accumulation × absorption in vivo,
concentration gradient is establishing
➢ flowing on a surface, sticking on a bottom (spirals), different
hydrodynamics in particular parts of solution
Dissolution methods – USP 1, 2
➢ USP 3 – equipment with reciprocating cylinder, closed
system
➢ simpler simulation of GIT conditions (pH changes and
transit times)
➢ product releasing in 6 different pH media
➢ suitable mainly for MR products, proof of drug form
against strong mechanic stress
Dissolution methods – USP 3
➢ USP 4 – flow-through cell, open system
➢ absorption process is simulated by keeping of concentration
gradient, no peristalsis
➢ suitable mainly for products containing low soluble API,
MR products, special dosage forms
Dissolution methods – USP 4
➢ paddle over disk, extraction cell
➢ for transdermal preparations
➢ 32 °C
Dissolution methods – USP 5
➢ rotating cylinder
➢ for transdermal preparations
➢ 32 °C
Dissolution methods – USP 6
Disolúcia - typy liekových foriem
➢ fast releasing dosage forms – minimum 85% within 15 min
➢ immediate releasing dosage forms – minimum 70 – 80%
within 30 – 45 min
➢ modified release dosage forms – dissolution lasts usually
8 – 24 h, specification minimum in three points in profile
➢ delayed release dosage forms – enterosolvent tablets
Dissolution – Requirements for dosage forms
Dissolution methods – Physiological approaches
➢ pepsin
➢ bile salts
➢ phospholipids (lecithin)
➢ lipase, pancreatic enzymes
➢ Ca2+ (lipase activity)
➢ ion power
➢ Fasted State Simulated Gastric Fluid (FaSSGF)
➢ Fed State Simulated Gastric Fluid (FeSSGF)
➢ Fasted State Simulated Intestinal Fluid improved version
(FaSSIF V2)
➢ Fed State Simulated Intestinal Fluid improved version
(FeSSIF V2)
Dissolution methods – Physiological approaches
➢ gastro-intestinal dissolution model TNO TIM-1
➢ full simulating of GIT (stomach, duodenum, jejunum, ileum,
pancreatic and bile secretion, enzymes, dynamic conditions,
peristalsis, body temperature, ion power)
Dissolution methods – Physiological approaches
To the colon
Peristaltic
pump
Stomach
(HCl pH 1.7,
NaCl, KCl, gastric
secretion)
Duodenum
(Bicarbonate buffer
pH 5, NaCl, KCl,
pancreatic and
biliary secretion)
Jejunum
(Bicarbonate buffer
pH 6, NaCl, KCl)
Ileum
(Bicarbonate buffer
pH 7, NaCl, KCl)
Temperature
probe
Heating
37 °C
➢ Golem
➢ Golem – user-friendly software
➢ Influence of bile and pancreatic juices (atorvastatin)
Examples
➢ Clopidogrel + acetylsalicylic acid (enterosolvent tablets)
0,000
0,100
0,200
0,300
0,400
0,500
0,600
0,700
0,800
0,900
1,000
0 10 20 30 40 50
c(mg/ml)
t (min)
Stomach ASA
Clopidogrel b.
SWIA0005 +
Bayaspirin b. H150
Clopidogrel + ASA b.
0A001
Clopidogrel + ASA b.
0A007
0,000
0,100
0,200
0,300
0,400
0,500
0,600
0,700
0,800
0,900
1,000
0 50 100 150
c(mg/ml)
t (min)
Duodenum ASA
Clopidogrel b.
SWIA0005 +
Bayaspirin b. H150
Clopidogrel + ASA
b.0A001
Clopidogrel + ASA
b.0A007
0,000
0,050
0,100
0,150
0,200
0,250
0,300
0,350
0,400
0,450
0 50 100 150 200 250 300
c(mg/ml)
t (min)
Jejunum ASA
Clopidogrel b.
SWIA0005 +
Bayaspirin b. H150
Clopidogrel + ASA b.
0A001
Clopidogrel + ASA b.
0A007 0,000
0,200
0,400
0,600
0,800
1,000
1,200
0 50 100 150 200 250 300
c(mg/ml)
t (min)
Ileum ASA
Clopidogrel b.
SWIA0005 +
Bayaspirin b. H150
Clopidogrel + ASA b.
0A001
Clopidogrel + ASA b.
0A007
Batch 0A001 and 0A007
Bayaspirin
Examples
➢ Atorvastatin (batches 80 and 82 vs. reference)
/thanks also to Dr. Čulen/
0
10
20
30
40
50
0 2 4 6 8 10 12 14 16 18 20 22 24
c(ng/ml)
t (h)
BES4
Reference 00 Batch 80
90% CI:
Upper limit = 127%
Criteria : 80 − 125%
NOT bioequivalent
0
5
10
15
20
25
30
0 50 100 150 200 250 300
%dissolved
t (min)
Batch 82
Reference 06 (no BES)
Batch 01
0
10
20
30
40
50
0 2 4 6 8 10 12 14 16 18 20 22 24
c(ng/ml)
t (h)
BES3 Reference 10 Batch 82
90% CI:
Lower limit = 100%
Upper limit = 121%
Bioequivalent
Criteria: 80 − 125%
Examples
➢ European Pharmacopoeia Ph. Eur.
➢ Czech Pharmacopoeia – Dissolution of solid dosage
forms, Dissolution of transdermal preparations,
requirements on particular dosage forms
➢ EMA guideline (European Medicines Agency) –
ICHQ2(R1) – method validation (accuracy, precision,
linearity, robustness, …)
Dissolution methods – Directives, guidelines
Rectal
Permeability
Placental
Permeability
Lung
Permeability
Absorption – Methods of administration, barriers
physical factors
(particle size, enhancers)
absorption
chemical factors
(lipophilicity, molecule size,
ability to be ionized
mechanism of absorption)
functional status of GIT
(motility, …)
formulation factors
(type of dosage form,
excipients, inhibitors and
enhancers of carriers, …)
drug interactions
(antacids, adsorbents, …)
method of administration
(i.m., p.o., …)
Absorption influencing factors
➢ ability to be ionized (pKa)
▪ important influence on drug solubility and permeability
(passive diffusion absorption – only nonionized form
is absorbed)
▪ many drugs are weak acids or bases
▪ Henderson-Hasselbalch equation
for acids: log ([HA]/[A-]) = pKa-pH
for bases: log ([BH+]/[B]) = pKa-pH
Absorption influencing factors – Chemical factors
➢ biological membrane
▪ coherent bilayer of lipid molecules with outer polar and
inner nonpolar part
▪ inserted proteins working as receptors, enzymes,
transport systems, keeping the shape, ...
Mechanisms of absorption
➢ paracelular × transcelular
▪ paracelular
• tight junction
• passive, diffusion (concentracion gradient),
• hydrophilic molecules with low Mr (cimetidin, atenolol)
paracelular transcelular
Mechanisms of absorption
▪ transcelular
• lipid diffusion: dissolution in membrane lipids, according
to concentration gradient, lipophilic drugs, nonionized
form (Henderson-Hasselbalch); majority of drugs
• diffusion across water pores: hydrophilic substances,
Mr till 150, low importance for drugs; Li
Mechanisms of absorption
▪ transcelular
• facilitated diffusion: with the aid of protein carrier, but
only on concentration gradient (protein oscillation);
AK-HEB
• active transport: against concentration gradient, energy
supply (ATP), with the aid of protein carrier (reversible
binding), one-way; levodopa
Mechanisms of absorption
▪ transcelular
• transport on ion pairs: quarter ammonia bases, neutral
complex with mucin, pure diffusion
• exocytosis and endocytosis, pinocytosis and fagocytosis
Mechanisms of absorption
➢ GIT anatomy
▪ stomach, small (duodenum, jejunum a ileum) and large
intestine
▪ length and surface of particular parts
➢ transit time
▪ dissolution, transporters, degradation
➢ local pH
▪ ionization level, acids, bases
Absorption influencing factors – Functional status
of GIT
➢ physiological parameters of GIT
Part of GIT Surface (m2) Length (m) Transit time (h) pH
stomach 0.053 – 0.5 – 1.5* 1.5 – 2
small
intestine**
200 6.5 (81 %) 3 – 4 6.0 → 6.5 →
7.0
large intestine 0.35 1.55 (19 %) 8 – 72 6.3
* transit time in oesophagus: a few seconds
** duodenum, jejunum, ileum
Absorption influencing factors – Functional status
of GIT
➢ physiological pH in GIT
Absorption influencing factors – Functional status
of GIT
➢ volume of gastric liquids
➢ local pH (solubility, dissociation)
➢ stomach filling (fasted × fed)
➢ speed of stomach emptying (size of bite, calories amount)
➢ gastrin (absorption increasing)
➢ somatostatin (absorption decreasing)
➢ bile salts (micelles, lipophilic drugs)
Absorption influencing factors – Functional status
of GIT
➢ surface area
➢ speed of peristalsis
➢ level of perfusion (congestion)
➢ activity of intestine microflora
➢ activity of digestive enzymes
➢ presystemic elimination: destruction in cells of intestine
epithelium, first pass effect, pass through lungs, … !!!
Absorption influencing factors – Functional status
of GIT
➢ originator companies: to find out, if a candidate has
suitable biopharmaceutical properties (peroral
absorption – marketing)
➢ generic companies: to find out, if a candidate has a same
absorption profile as original product
Usage of absorption models
➢ experiments performed
▪ in silico
▪ in vitro
▪ in situ
▪ in vivo
Absorption models
➢ computer models
▪ on basis of information about a structure and data from
preceding in vivo experiments, counting of absorption
of new substances
▪ important factors lipophilicity, hydrogen bindings, inter- and
intramolecular bindings, charge, molar weight prediction
of passive transport
▪ QSAR (Quantitative Structure – Activity Relationship)
Experiments performed in silico
!!! together with in silico methods – saving of animals !!!
➢ chromatographic methods
➢ artificial lipid membranes
➢ cell cultures
➢ parts of small intestine
➢ (SHIME)
Experiments performed in vitro
➢ chromatographic methods
▪ stationary phase resembling lipid bilayer or immobilised
phospholipids or liposomes
▪ only interaction with lipid bilayer, not a transportation
across a membrane
Experiments performed in vitro
➢ artificial lipid membranes
▪ hydrophobic porous filter impregnated with phospholipids
▪ prediction of passive diffusion, transportation across
a membrane
▪ PAMPA (Parallel Artificial Membrane Permeation Assay)
12 thousand CZK / 5 plates
Experiments performed in vitro
PVDF - polyvinyliden fluorid
➢ PAMPA
Experiments performed in vitro – PAMPA
%ofabsorption
➢ comparison of nanonized and standard API
%ofabsorption
API Particle size (nm)
(Nano API (x90))
Particle size (μm)
(standard API)
Meloxicam 290 20
Valsartan 697 30
API Permeability (%)
(Nano API)
Permeability (%)
(standard API)
Meloxicam 20.8 9.8
Valsartan 56.0 10.7
Experiments performed in vitro – PAMPA
➢ cell cultures
▪ prediction of transportation across a cell membrane
including active transport
▪ Caco-2 cells 10 500 – 22 500 CZK / 1 compound
Experiments performed in vitro
➢ Caco-2 cells
▪ cells of human adenocarcinoma of large intestine (colon)
▪ suggested for simulation and prediction of intestinal drug
absorption after oral administration
▪ dispose of enzymatic and transportation systems
(with limitations – low capacity)
▪ correlation with in vivo data has shown that Caco-2 cells are
able to predict absorption in vivo and identify low
permeable substances; BCS classification
▪ low amount of tested compound
▪ not possible to distinguish differences in absorption
in particular parts of small intestine, better for APIs than
drug forms, narrow range of working pH, time consuming
Experiments performed in vitro
➢ parts of small intestine
▪ human
▪ rat, dog
▪ Ussing chamber
▪ absorption in particular parts
Experiments performed in vitro
➢ SHIME (Simulation of the Human Intestinal Microbial System):
▪ model, which simulates physicochemical and enzymatic
conditions and contains bacterial colonies
resembling colonies situated in human GIT
▪ multi-compartment 5-step system, 2 steps small intestine,
3 steps large intestine
▪ decomposition of active molecule × prodrug (Sulfasalazin)
Experiments performed in vitro
➢ perfused organs
▪ comparison of isolated absorption
▪ solution, solid dosage forms
▪ mass balance
▪ small sample series – surgical adjustment
▪ anaesthesia
Experiments performed in situ
➢ animal models
▪ mouse 6 000 USD / 1 compound
▪ rat
▪ guinea pig
▪ dog
▪ pig
▪ mini-pig
▪ ape
▪ surgical adjusted (probes etc.)
▪ there is not a single universal suitable mate of animal model
Experiments performed in vivo
Thank you for your attention