pharmacokinetics of dgavp in plasma following intranasal and oral administration to healthy subjects

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Peptides, Vol. 15, No. 6, pp. 1101-1104, 1994 Copyright © 1994 Elsevier Science Ltd Printed in the USA. Aft fights reserved

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Pharmacokinetics of DGAVP in Plasma Following Intranasal and Oral Administration to

Healthy Subjects

H. G. M. W E S T E N B E R G , *1 R. HIJMAN,* V. M. W I E G A N T / f F. L A C Z I t A N D J. M. V A N REEI"

Rudolf Magnus Institute of Neurosciences, *Departments of Psychiatry and i'Pharmacology, Utrecht University, The Netherlands

Received 16 March 1994

WESTENBERG, H. G. M., R. HIJMAN, V. M. WIEGANT, F. LACZI AND J. M. VAN REE. Pharmacokinetics ofDGA VP in plasma following intranasal and oral administration to healthy subjects. PEPTIDES 15(6) 1101-1104, 1994.--A pharmacokinetic study was carried out to assess the bioavallability of desglycinamide-[ArgS]vasopressin (DGAVP, Org 5667). DGAVP (2 mg) was administered both intranasally and orally to healthy subjects with a treatment interval of 1 week. Blood samples were taken regularly between 15 min before and 210 min after administration and were assayed for DGAVP by radioimmunoassay. In all subjects endogenous vasopressin (AVP) levels were detectable. Peak levels of DGAVP occurred at 15 rain after both treatments. The mean absorption half-life was 8.7 and 7.3 min and the mean elimination half-life was 38 and 34.6 min for the intranasal and oral route of administration, respectively. The bioavailability of orally administered DGAVP was low compared with the intranasally administered drug; the relative bioavailability of oral/nasal administration was 0.7%. The results indicate that DGAVP is absorbed rapidly after both oral and intranasal administration, but the intranasal route of administration of DGAVP is 100 times more effective in increasing plasma DGAVP levels.

DGAVP Pharmacokinetics Healthy subjects

CLINICAL trials have been performed with different vasopressin congeners, including synthetic naturally occurring vasopressins, [ArgS]vasopressin (AVP) and [LysS]vasopressin (LVP), an ana- logue of AVP (1-desamino-D-arginine-vasopressin, DDAVP), and a fragment of AVP (desglycinamide-[Arg8]vasopressin, DGAVP) to evaluate the effects ofvasopressin (VP) on cognitive disturbances in humans (8,9,21). The dose of VP that can be used is limited, because of the endocrine effects of the peptide on blood pressure and water retention. DDAVP is a more se- lective peptide in that it affects water retention, but not blood pressure. Removal of glycinamide from VP almost completely eliminates these peripheral effects, yet DGAVP retains considerable CNS effects, as assessed in animal studies (4). DGAVP should therefore be favored above DDAVP, AVP, and LVP to investigate the influence of these peptides on cognition in humans.

For neuropeptides, it is important to know whether system- ically administered compounds are transported into the central nervous system. The most widely held view is that neuropeptides poorly cross the blood-brain barrier. Several studies have been conducted to investigate the permeability of the blood-brain barrier to vasopressin analogues, but by and large the results are

inconsistent ( 1,3,11,12,15-17). These inconsistencies with regard to the permeability of the blood-brain barrier to AVP and its congeners, however, can be largely explained by the existence of a carrier-mediated and saturable brain to blood transport system for AVP (2). This transport system may prevent AVP accumulation in the brain following increases of the neuropeptide in the periphery. When the brain is exposed to high amounts of neuropeptide, however, this transport system may become saturated, so that accumulation can occur.

Information on the pharmacokinetics and bioavailability of DGAVP is therefore essential for a proper understanding and evaluation of the clinical data. On the other hand, there are also brain region where some leakiness of the blood-brain barrier can be observed. A study done by Riekkinen et al. (13) shows that DGAVP can easily cross the blood-brain barrier in humans a~er intranasal administration. Intranasal application is therefore the most frequently used route of administration of DGAVP to humans, although it has the disadvantage that the dose cannot be controlled accurately and administration is difficult if subjects suffer from rhinitis. A considerable amount of intranasally administered DGAVP (about 2 mg) was absorbed into the blood of healthy volunteers (unpublished data, Organon International

Requests for reprints should be addressed to Dr. H. G. M. Westenberg, Department of Psychiatry, Academic Hospital Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands.

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1102 WESTENBERG ET AL.

B.V., The Netherlands). Oral administration has been found effective in rats (20). In heroin addicts, sublingual administration of DGAVP has a beneficial effect on methadone detoxification (6,18).

Over the past years, our group has conducted several clinical trials into the efficacy of DGAVP in the treatment of cognitive dysfunctions (7). DGAVP is particularly effective in patients with memory impairment due to light brain concussion. In these studies DGAVP was administered via the oral or the intranasal route.

It was assumed that the intranasal route is more efficient than the oral route because of the susceptibility of peptides to metabolic degradation in the gastrointestinal tract. However, this was not reflected in the results of the clinical studies, which did not show marked differences between the two routes of administration. It was therefore deemed of interest to investigate the bioavailability of the peptide after administration by both routes.

METHOD

Subjects

Nine healthy volunteers (five females, four males), aged 25- 39 years, participated in the study. All subjects gave their in- formed consent and the study was approved by the Medical Ethical Committee of the Academic Hospital of Utrecht Uni- versity. Subjects with rhinitis or other conditions that preclude the absorption of drugs after intranasal administration were excluded as well as those who were pregnant or at risk of pregnancy. All subjects were drug free.

Design

All subjects received DGAVP (Org 5667) twice; on the first occasion the drug was administered via the nasal route and on the second occasion via the oral route. The interval between treatments was 1 week. For intranasal administration, a spray containing DGAVP dissolved in saline was used (one puff per nostril). For oral administration, DGAVP was dissolved in saline to a concentration of 0.2 mg per ml. A total of 10 ml was given as a single dose in the fasting state. Blood samples for the de- termination of DGAVP were taken from the antieubital vein with plastic disposable syringes. Samples of approximately 10 ml of blood were taken 15 and 5 min before and 5, 15, 30, 60, 90, 120, 180, and 210 minutes after DGAVP administration. Heparinized blood (200 IU heparin/10 ml blood) was transferred to plastic tubes (5 ml blood per tube) and immediately cooled on ice. After centrifugation at 4°C, plasma samples were stored at - 7 0 ° C until analyzed.

Determinat ion o f D G A V P

DGAVP was assayed by radioimmunoassay (RIA) using antiserum W4E, basically as described previously (5,19). Syn- thetic DGAVP was used as standard and in radioiodinated form (Iodogen method) (14) as tracer. RIAs were performed in Veronal buffer, pH = 8, containing 5 mg human serum albumin per ml (RIA buffer). RIA buffer was used for the dilution of standards (0.25-32 pg per tube), samples, tracer (about 10,0000 cpm per tube), and antiserum (final dilution 1:48,000).

Assays were carried out at 4°C in a total volume of 110 #1 under nonequilibrium conditions (preincubation 48 h; incu- bation 24 h). Separation of bound and free DGAVP was performed by precipitation with polyethylenegiycol (1 ml; 30% w/v) after the addition of 50 #1 horse serum as carrier protein. Standard curves were calculated by linear regression analysis

after logit-log transformation of the data. The antiserum showed partial cross-reactivity with AVP (35.6%) and negligible cross- reaction with AVP(1-7) (1.6%) and [Cyt6]AVP(2-8) (0.2%). The detection limit of the assay was 0.25 pg DGAVP per tube (at 10% displacement of tracer).

DGAVP was extracted from 1-ml plasma samples with ther- mally activated Vycor R glass powder (5). Extractions were car- fled out in duplicate. Dry residues were redissolved from RIA buffer and 50-#1 aliquots were assayed for DGAVP-IR in duplicate. The results were calculated by interpolation in the RIA standard curve. The data were not corrected for recovery of the extraction procedure.

Pharmacok ine t i c Analyses

The intranasal data could best be described by an open two- compartment model with first-order absorption. The equation describing the relationship between the plasma concentration and time, according to this model, is: Cppl = A . e-~t + B . e-at - C. e - k a . t, where a and ~ are the distribution and elimination rate constants, respectively, and ka is the absorption rate con- stant.

The biological half-life of the drug is represented by t~/2a = In 2//3. Similarly, the tt/2abs = In 2/ka and tt/2~ = In 2/a. The total area under the plasma concentration-time curve (AUC) (i.e., from time zero to infinite) can be calculated from: Ct = B /

+ A / a - C/ka . The mean value of two pretreatment deter- minations ( -15 and - 5 min) was taken as the basal plasma concentration.

The oral data could best be fitted to an open one-compartment model with first-order absorption. The equation describing this model is: Cpl = A . e -ke" ~ - B . e -k~'t, where ke and ka are the elimination and absorption rate constants, respectively. The biological half-life of the drug is given as tt/2 = In 2/ke. The total AUC is: AUC = A / k e - B /ka .

The relative bioavailability (oral/intranasal), that is, the frac- tion of the administered oral dose absorbed relative to that of the same dose administered intranasally (F,~l), was calculated from the ratios of the AUCs of the oral and intranasal data.

The data were fitted by computer with a NONLIN program using a Quasi-Newton minimization program.

RESULTS

TWO subjects had a high DGAVP-IR level (75.9 and 75.9 log/ ml, respectively) before oral administration of DGAVP. This is probably due to an increase in native AVP levels resulting from stress associated with venapunction (10). One of these subjects also had a high AVP level (155.3 pg/ml) before intranasal administration of the drug. The data from this subject (intranasal and oral) and subject 3 (only oral) were excluded from the analyses.

The mean plasma levels of DGAVP-IR after intranasal and oral administration are depicted in Figs. 1 and 2, respectively. A clear-cut increase in DGAVP-IR was found after intranasal DGAVP administration, with a peak at 15 min. Levels returned to basal values within about 3 h. Oral administration also in- creased plasma DGAVP-IR, albeit less than after nasal administration. The peak levels occurred 5-15 rain after administration, and were about 100 times lower than those found after intranasal administration. The levels returned to basal values within about 2 h after administration.

Basal levels of DGAVP-IR were detectable (2.0-8.2 pg/ml) in all subjects (Tables 1 and 2). The mean absorption half-life after intranasal administration was 8.7 rain (range 2.2-13:0). The absorption phase was followed by a rapid distribution phase

DGAVP, P H A R M A C O K I N E T I C S IN H E A L T H Y SUBJECTS 1103

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T ime (min)

FIG. 1. Plasma concentration-time curve of DGAVP-IR in eight healthy volunteers following intranasal administration of 2 mg DGAVP (ORG 5667). The curve was fitted to the data of all subjects assuming a two- compartment open pharmacokinetic model with first-order absorption, using a NONLIN program. The data points are the mean values at the different time points.

with a mean half-life of 10 min (range 1.8-15.0). The drug was eliminated with a mean half-life of 38.0 min (range 15.0-57.8).

The half-life values estimated from the oral data were com- parable to those obtained from the intranasal data. The mean half-life of absorption and elimination was 7.3 (range 0.2-27.0) and 34.6 min (range 7.7-69.0), respectively. The bioavailability of D G A V P after oral administration was lower than that obtained after intranasal administration (the mean F ~ was 0.7%).

DISCUSSION

Intranasally administered D G A V P rapidly appeared in the general circulation, with peak values occurring 15 min after administration. Oral administration of D G A V P also resulted in a rapid increase in D G A V P immunoreact ivi ty in plasma, albeit peak values were much lower than after intranasal administration. Although the absolute bioavailability cannot be assessed from the present experiments, as intravenous data are lacking, obviously the amount of D G A V P absorbed through the nasal epithelium is much larger than through the gastrointestinal tract. This can be accounted for in part by the absence of gastrointes-

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150 20O 250

T ime (min)

FIG. 2. Plasma concentration-time curve of DGAVP-IR in seven healthy volunteers following oral administration of 2 mg DGAVP (ORG 5667) as a solution. The curve was fitted to the data of all subjects assuming a one-compartment open pharmacokinetic model with first-order absorption. The data points are the mean values at the different time points.

TABLE 1

PHARMACOKINETIC PROFILE OF DGAVP AFTER INTRANASAL ADMINISTRATION

C~a* C=~ t,/2 abs tl/2= tt/2~ AUC Subj. (pg/ml) (pg/ml) (min) (rain) ( m i n ) (pg/ml/h)

1 2.6 2949 10.8 13.0 57.8 2694 2 6.7 613 9.9 10.5 49.5 660 3 2.8 1359 5.2 6.1 36.5 1251 4 4.2 542 13.0 15.0 15.0 529 5 2.6 1873 10.4 12.8 49.5 2513 6 7.1 736 12.0 13.9 40.8 768 7 6.0 358 6.2 6.5 33.0 317 8 2.0 1727 2.2 1.8 22.0 1320

Mean 4.3 1269 8.7 10.0 38.0 1257 SD 2.1 884 3.8 4.7 14.5 898

* Mean value of the two pretreatment data.

tinal degradation and hepatic first-pass metabolism. The present study shows that the intranasal route of administration is 100 times more effective in increasing the plasma levels of D G A V P than the oral route. It should be emphasized that the D G A V P concentrations may have been underestimated, because it cannot be ruled out that D G A V P administration decreases the endogenous release of AVP by the pituitary. This is important for the oral data where the levels of DGAVP-IR were low. The greater systemic availability after intranasal administration may result in much greater availability of the neuropeptide at the site of action, because the etilux system (2) will become saturated when it is exposed to high levels of AVP analogues. An additional advantage of the intranasal route of administration is the possible transport of drug directly into the brain and the CSF by diffusion through the olfactory epithelium (l 3). It is interesting to note that, although the bioavailability following oral administration was poor, peak plasma D G A V P levels were attained already after 5 min in five out of seven subjects. The rapid appearance of D G A V P in the general circulation after oral administration is hard to explain by absorption from the gastrointestinal tract. A more plausible explanation for this phenomenon could be that D G A V P is absorbed through the epithelial lining of the mouth, which, like the rest of the alimentary tract, behaves as a lipid-like barrier to the passage of drugs. In view of the high

TABLE 2

PHARMACOKINET1C PROFILE OF DGAVP AFTER ORAL ADMINISTRATION

Cb,~ C ~ t~r2 alas tl/2 AUC F~ Oral/Nasal Subj. (pg/ml) (pg/ml) (rain) (min) (pg/ml/h) (%)

1 2.1 6.7 27.0 69.0 8.7 0.2 2 6.7 18.5 13.9 15.8 3 0.5 3 . . . . . .

4 2.4 6.5 3.5 46.2 4.5 0.9 5 2.0 11.5 0.2 17.8 4.6 0.2 6 8.2 26.2 5.5 7.7 8.2 1.1 7 4.7 9.9 0.2 16.5 2.4 0.8 8 3.4 13.2 0.6 69.0 17.5 1.3

Mean 4.2 13.2 7.3 34.6 7 0.7 SD 2.4 7.1 10.1 26.4 5.2 0.4

1104 WESTENBERG ET AL.

vascularity of the oral cavity, sublingual or buccal administration generally results in a rapid absorption of many compounds, including peptides. If this reasoning is correct, the bioavailability of DGAVP after oral administration in other dosage forms (e.g., capsules) can be expected to be negligible.

The plasma concentra t ion- t ime curve of DGAVP after intranasal administration could best be described by a two-compartment pharmacokinetic model, suggesting diffusion into less rapidly perfused organs or permeation across certain barriers

into less accessible tissue. Like most peptides, the elimination half-life of DGAVP was short (about 35 min). Rapid elimination has also been reported by Riekkinen et al. (13). Whether this rapid clearance is due to metabolic degradation or to renal or hepatic el imination is yet unknown. This short half-life of DGAVP may hamper its usefulness in the treatment of cognitive dysfunctions, assuming a relationship between brain concentration and clinical effect. Intranasal administration seems to be the route of choice for further clinical trials with DGAVP.

R E F E R E N C E S

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2. Banks, W. A.; Kastin, A. J.; Horvath, A.; Michals, E. A. Carrier- mediated transport of vasopressin across the blood-brain barrier of the mouse. J. Neurosci. Res. 18:326-332; 1987.

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6. Fraenkel, H. M.; van Beek-Verbeek, G.; Fabriek, A. J.; van Ree, J. M. Desglycinamide9-arginineS-vasopressin and ambulant methadone-detoxification of heroin addicts. Alcohol Alcohol. 18:331- 335; 1983.

7. Hijman, R.; Joiles, J.; Verhoeven, W. M. A.; van Ree, J. M.; Elderson, A.; de Wied, D. Desglycinamide-(ArgS~-vasopressin in five trials with memory-disturbed patients. Hum. Psychopharmacol. 7:7-23; 1992.

8. Jolles, J. Vasopressin-like peptides and the treatment of memory disorders in man. In: Cross, B. A.; Leug, G., eds. The neurohypo- physis: Structure, function and control. Amsterdam: Elsevier;, 1983: 169-182.

9. Jolles, J. Vasopressin and human behavior. In: Gash, D. M.; Boer, G. J., eds. Vasopressin principles and properties. New York: Plenum Press; 1987:549-578.

10. Laczi, F.; Burbach, J. P. H.; van der Kleij, A. A. A. M.; de Wied, D.; Wiegant, V. M. Vasopressin(1-8) (desglycinamide9-[ArgS]vaso - pressin) is an endogenous peptide present in rat plasma. Peptides 12:329-342; 1991.

I 1. Legros, J. J.; Gilot, P.; Semn, X.; et al. Influence of vasopressin on learning and memory. Lancet 1:41-42; 1978.

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13. Riekkinen, P.; Legros, J. J.; Sennef, C.; Jolkkonen, J.; Smitz, S.; Soininen, H. Penetration of DGAVP (Org 5667) across the blood- brain barrier in humansubjects. Peptides 8:261-265; 1987.

14. Salacinsky, P.; Hope, J.; McLean, C.; et al. A new simple method which allow theoretical incorporation of radio-iodine into proteins and peptides without damage. J. Endocrinol. 81:31 ; 1979.

15. Simon-Opperman, C.; Gray, E.; Szczepanska-Sadowska, E.; Simon, E. Vasopressin in blood and third ventricle CSF of dogs in chronic experiments. Am. J. Physiol. 245:541-548; 1983.

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17. S6rensen, P. S.; Vilhardt, H.; Gjerris, F.; Warberg, J. Impermeability of the blood-cerebrospinal fluid barrier to l-deamino-8-D-arginine- vasopressin (DDAVP) in patients with acquired, communicating hydrocephalus. Eur. J. Clin. Invest. 14:435-439; 1984.

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pharmacokinetics of dgavp in plasma following intranasal and oral administration to healthy subjects

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