Transfersulin® was prepared from a commercially available regular solution of human recombinant insulin (Actrapid® 100 HM; Novo Nordisk), which was either ...
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Transfersome® compositions are described in the patents mentioned previously in the text.
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lated in the carriers. This indicates that Transfer
some® mediated drug delivery through the skin is
transport across intact skin is the delivery of carrier
little affected by the molecular size of the carrier associated active ingredient. Measurements of 1251 or 3H radioactivity show that Transfersome® mediated non invasive delivery across the skin leads to similar biodistribution
associated active ingredient into the viable epider
profiles as a subcutaneous injection of the drug. The
mal tissue, just below the skin barrier. Here, small
epicutaneous
and soluble drugs tend to dissociate from the carriers
more time to reach the final state and results in lower systemic, but increased local, drug concentration at
3. Basic Biodistribution The first step of Transfersome® mediated drug
and diffuse into the bloodstream. In contrast, larger molecules are distributed in the skin via interstitial fluid flow. Such flow also helps to bring material
administration,
however,
requires
the beginning of the transportation process. This
could influence the biological fate of the drug.
into deep tissue below the application site. In light of the available pathway areas, it is initially relatively
unlikely that aggregates will enter lymphatic vessels
4. Pharmacokinetic Considerations
in the dermis via fenestrations and then progress
The lag time for Transfersomes® crossing the
further into the systemic blood circulation. The deep
skin can be as short as 15 minutes in rodentsm] and
tissue penetration therefore prevails early after
humans (unpublished data). The pharmacokinetic
Transfersomes® application. At later times, how
profile of drugs delivered through the skin with
ever, after local tissue saturation, entry into the
Transfersomes® therefore depends on the average
blood via the lymph gains importance. Previous
rate with which Transfersomes® cross the skin and
experience with subcutaneously injected lipid vesi
on the kinetics of drug release from the carri
cles,l31] scrutiny of published biodistributionww] or
ers.[7>13=26 271 The delivery rate depends on the carrier
pharmacokinetic[9*32] results and unpublished data support such notions. Several lines of evidence suggest that stability
composition and design, on the applied carrier dose,
and on other application parameters. The release
optimised ultra deformable vesicles overcome the
rate is also affected by drug characteristics. If small and rapidly released molecules, or those
skin barrier as large entities, if not essentially in
with a low affinity for the carrier, are administered
tact.l331 An indication for this is the clearance of
on the skin in sufficient quantity they start appearing
Transfersome® derived lipids by the reticulo endo
in the blood in significant quantity within l hour
thelial system, especially in the liver or spleen,[26]
after administration.l8"°3 In contrast, large mole
which is common to the elimination of most aggre gates from the blood.[31]
first accumulate in the skin, then fill the subcutane
cules, or those with a high affinity for the carrier,
To study Transfersome® mediated drug delivery
ous reservoir, and finally enter the blood via the
through the skin, animal experiments were carried
lymph. Detailed analysis of the effects of drug size
out using 3H or 14C labelled drugs associated with
(figure 1), lipophilicity,[13] carrier composition[91 and applied dose (unpublished data) vindicates the conclusion. The minimum lag time for such drug
different carriers. This revealed that lipophilic low
molecular weight drugs, such as testosterone (288 Da), triamcinolone acetonide (434 Da) and other
redistribution is two hours.l9l For the less deforma
steroids, but also other fat soluble drugs, appear in
ble or more diluted carriers, this value even can be
the blood at times comparable to those measured
up to 8 10 hours,[7’1°’27] depending on the applied
with empty carrierslll Similar results were obtained
amount of drug and carrier or the application area.
with high molecular weight water soluble drugs,
In order to define the characteristics of a specific
such as calcitonin, heparin or dextran (3432, 7500 and 70000 Da, respectively) originally encapsu
drug or formulation, pharmacokinetic studies have
© Adis Data Information BV 2003. All rights resen/eol.
been performed by injecting Transfersome® formu
Clin Pharmacokinet 2003; 42 (5)
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Ultradeformable Carriers for Transderinal Insulin
I
Epicutaneous
O
Subcutaneous
6 ._
125i Calcitonin
_k&i/(f*tr~r
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125i Serum albumin
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8
Fig. 1. Pharmacokinetics in mice oi macromolecules in Transtersomes® applied on the skin (closed symbols) or injected subcutaneously
(open symbols) in simitar amounts. The systemic drug derived label concentration is of comparable magnitude for all tested proteins at 4 8 hours after epicutaneous administration, indicative of constant transcutaneous carrier transport and drug release. In contrast, the rate of elimination of the injected drug varies and seems to depend on the size and/or the interaction of macromolecules with carriers”! (modified and extended iromlzel).
lations of different labelled proteins under the skin
lin/C peptide concentration ratio was found to re
and by applying corresponding carrier suspensions on the skin surface. Figure 1 gives representative
semble closely the glucodynamic profile in the blood, with either value reaching a plateau 4—6 hours after administration. Figure 2 illustrates this observation and indirectly confirms a rapid dissocia tion of the drug Transfersomes® complex, followed by the drug action, once the skin barrier has been
comparative data for three different macromole cules. The relatively low early serum concentrations
of larger proteins reflect the effects of increasing drug size or carrier affinity on protein release kinet ics in the body. The pharmacokinetics of human recombinant in sulin combined with Transfersomes® (Transfersu lin®) first was tested in healthy human volunteers. The change in appropriately normalised serum insu © Aclis Data Information B\/ 2003. All rights reserved.
crossed.
4.1 Absorption
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In vitro methods for studying transdermal migra tion of Transfersomes® rely on skin biopsy punches Clln Pharmacokinet 2003.‘ 42 (5)
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Time atterTranslersulin® application (h) Fig. 2. Pharmacokinetic and pharmacodynarnic characteristics of insulin in Transfers0mes® applied on intact skin of a healthy human volunteer. The temporal increase of relative concentrations ot insulin and its co product, C peptide, in the blood proves the delivery of
exogenous hormone through the skin. Parallel decrease of the serum glucose concentration is indicative of the biological activity of non invasively delivered drug. Data points represent mean values from three independent experiments. Vertical bars give standard deviation of
the mean. or on analysis of vacuum pulled skin blisters. Both are preferably done with fresh human or porcine skin, but at best yield indicative data, owing to the
lack of proper intercellular fluid motion in excised skin. In case of rhodamine labelled Transfer somes®, stratum corneum penetration is detectable after less than l hour; however, a much greater quantity of the label is recovered in epidermis or
dermis 8—l2 hours later (A. Schatzlein, unpublished data). Skin penetration experiments done with Trans fersomes®in vivo revealed that the preferred path of the vesicle transport through the barrier always in
volves the regions of lowest skin penetration resis tance. These are typically located between intercel lular lipids and corneocyte membranes in the stra © Adis Data Information BV 2003. All rights reserved.
tum corneum or else between the stacks of intercellular lipid lamellaelm The data also confirm the essential role of hydration gradient across the skin that provides the necessary energy for the skin penetration by Transfersomes®.[112830] The question remains open as to whether or not highly elastic vesicles cross the skin intact.[33’34] However, no
doubt exists about the transcutaneous pathway opening by,[1'°"*22=35] and the superior barrier penetra tion ability of, elastic/deformable vesiclesllzim in comparison with conventional liposomeslzfi 303837] or mixed micelles.[26=30*38l In a representative study,[9] Transfersomes® la belled with [3H]phosphatidylcholine or loaded with 3H labelled inulin (~5000 Da) were applied on in tact murine skin or were injected subcutaneously.
Clin Pharrnacokinet 2003; 42 (5)
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Ultracleformable Carriers for Transdermal Insulin
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Fig. 4. Pharmacodynamics of insulin applied on the skin in Transfersomes® (epicutaneous [e.c.]; closed symbols) or injected under the skin
(subcutaneous [s.c.]; open symbols) in the form of ultralente insulin (Ultratard®, Novo Nordisk). Very similar glucodynamic response is measured in human volunteer with both tested formulations, despite the fact that the drug reservoir is on the skin in the former and in subcutaneous tissue in the latter case. Transfersulin® HC, with 250 IU/ml, appears to be somewhat more potent on per dose basis than Transtersulin® C, with 50 IU/ml, possibly due to the higher carrier payload in the former formulation. Full and dashed lines give the results of nearest neighbours averaging for e.c. and s.c. application, respectively.
acting insulin,[39] which is under development by several biotechnological companies. I 4.3 Metabolism oncl Eliminotion Insulin associated reversibly with Transfer somes® on the skin appears to be released rapidly after the carriers have reached the watery in tracutaneous tissue. A modern Transfersulin® for mulation therefore lowers the blood glucose concen tration as rapidly and efficiently as an injected solu tion of ultralente insulin (see figure 4 and figure 5). © Aclls Doro Information B\/ 2003. All rights reserved.
The similar biological effects of injected ul
tralente insulin and of epicutaneously administered Transfersulin®, the results of comparative biodis tribution studies, and general appearance of the drug in the gut, thus together support the hypothesis that the drug from Transfersomes® is processed and biodggmded Similarly to free injected drug
5. Therapeutic Experience and |mp|icqfi°ns Earlier tests with healthy volunteers eenfirmed the feasibility of non invasive transdermal insulin Clin Pnorrnocokinet 2003: 42 (5)
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Ultradeformable Carriers for Transdermal Insulin
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_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .
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Fig. 5. Glucodynamics measured in patients with type 1 diabetes mellitus before and after an epicutaneous administration of insulin in highly deformable carriers, Transfersomes® (filled symbols), or in solution, non optimised vesicles or micelles, which as a group served as a negative control (open symbols). Times of regular insulin injections are shown with an asterisk. Error bars or shaded zones define the 95% confidence range for the individual experiments or groups, respectively; when not seen, this range is smaller than the symbol. n gives the appropriate total number of experiments done with various experimental formulations on each patient. (a) Patient treated up to 2 hours with a subcutaneous continuous insulin infusion (CSll) and then with Transfersulin® T. (b) Patient on intensified insulin pre therapy until —8 hours treated epicutaneously with 'l'ransfersulin® T (3—5>< basal daily dose) or subcutaneously with an injection of ultralente insulin (1>< [full curve] or 0.4>< [broken curve] of daily basal dose). (c) The patient on intensive insulin therapy received Transiersulin® C (filled symbols) or the negative control formulations specified above (open symbois) on the skin. Insets give the net change in blood glucose concentration,
2 r5»
defined as the difference between experimental and negative controt results. Ticks on the main and insert axes correspond.
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© Aclis Doto lnformotion BV 2003. All rights reserved.
Clin Phormocokinet 2003; 42 (5)
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