Biomedical Engineering Reference
In-Depth Information
ml after oral application [
79
]), cimetropium, granisetron, tropisetron and trospium
(about 6 ng/ml after oral dosing [
61,
71,
73,
83,
84
]), and scopolamine (13 ng/ml
after i.v. injection [
97
], 7 ng/ml after 15 min i.v. infusion [
98
] , 0.25-1.3 ng/ml after
nasal administration [
88
] ) (Table
5
). Corresponding MS/MS transitions are sum-
marized in Table
9
.
Whereas PK studies referred above required analysis of drugs in the circulation,
distribution studies discussed next were performed to investigate drug transfer into
or through other compartments.
3.4.2
Distribution Studies
Van Zyl et al. reported on the diffusion of ipratropium through porcine bronchial
epithelium tissue [
74
]. In principle, ipratropium is administered via the respiratory
tract by inhalation to treat pulmonary diseases associated with bronchoconstriction.
Therefore, pulmonary absorption by bronchial tissue determines its local efficacy
and was thus investigated in a diffusion cell in vitro. Bronchial epithelium was
equilibrated in PBS and discs of 4 mm
2
were mounted on that diffusion cell separat-
ing the donor and receiver compartment. The donor compartment contained the
drug dissolved in PBS (1 mg/ml) and the receiving chamber was permanently
flushed with a low flow (1.5 ml/h) of PBS thus allowing time-resolved fractionation
for subsequent direct analysis by LC-ESI MS/MS in MRM mode. Transition to the
product ion at
m
/
z
124 was monitored for quantification (Table
9
). The transfer of
ipratropium was characterized by the flux (about 220 ng/cm
2
/min) and the permea-
bility coefficient calculated to be 1.6 × 10
−8
cm/s.
Whereas ipratropium is inhaled for therapy, the MR agonist (−)-Sat (Fig.
1
) is
thought to be directly dropped into the eye to treat glaucoma and reduce IOP [
85
] .
Therefore, penetration of satropane into the anterior chamber determines its thera-
peutic efficacy. Accordingly, Fu et al. analysed this process in an in vivo study using
anaesthetized rabbits. A linear probe was implanted in the centre of the anterior
chamber of dilated rabbit pupils. Perfusion was performed at 2 ml/min with isotonic
PBS. Satropane was instilled into the eyes and microdialysates were collected after
distinct periods of time for subsequent direct LC-ESI MS/MS analysis in MRM
mode. Transition from the
m
/
z
354 precursor ion to the product ion at
m
/
z
182 was
monitored for measurement as listed in Table
9
. Matrix effects of aqueous humour
dialysates caused about 18 % suppression of satropane ionization but allowed reli-
able quantification. Even though the paper of Fu et al. presents careful method vali-
dation no physiological data on drug distribution were provided.
Callegari et al. characterized the central nervous system (CNS) penetration of
the QTA trospium and methyl scopolamine as well as of the TTA scopolamine [
77
] .
Therefore, they performed in vivo studies administering the drugs to rats subcuta-
neously. After 1 h animals were euthanized, cerebrospinal fluid (CSF) was taken
from cisterna magna and brains were removed and homogenized. Whereas CSF
was mixed with IS (atropine) to be directly injected for LC-ESI MS/MS analysis,
brain homogenates were extracted by SPE on Oasis HLB material subsequent to IS
