BIOPHARMACEUTICS & DRUG DISPOSITION, VOL. 12, 537-546 (1991)

PHARMACOKINETICS AND BIOAVAILABILITY OF PAPAVERINE HCl FOLLOWING INTRAVENOUS, PERORAL, RECTAL, VAGINAL, TOPICAL AND BUCCAL ADMINISTRATION IN BEAGLE DOGS CHRISTIAN KRAUS, AMEERA SHAAYA, JOACHIM ULMER, DAWN HUTCHINGS, ANIL MENON, ADEL SAKR AND WOLFGANG A. RITSCHEL*

Division of Pharmaceutics and Drug Delivery Systems, University of Cincinnati Medical Center. Cincinnati, Ohio,USA.

ABSTRACT This in vivo study was designed to obtain bioavailability data and a definite pharmacokinetic profile of papaverine HCl in Beagle dogs following intravenous (IV), peroral (PO), rectal, vaginal, topical, and buccal administration of different papaverine HCl formulations. Blood samples were analyzed by high-performance liquid chromatography. The pharmacokinetic parameters were determined using either a curve fitting program (RESID) or a compartment model independent program (AUC-RPP). The plasma concentration-time profiles show that papaverine HCl pharmacokinetics is best described by an open two-compartment model. The absolute bioavailability of papaverine HCl was determined to be 57.2 per cent, 25.2 per cent, 53.2 per cent, 3.2 per cent and 7.5 per cent, respectively, following P.O., rectal, vaginal, topical and buccal administration. KEY WORDS

PapaverineHCI Pharmacokinetics Bioavailability Beagle dog and extravascularadministration

Intravascular

INTRODUCTION Papaverine is a benzylisoquinoline alkaloid, which can be prepared synthetically or is obtained from opium.' Papaverine acts as a peripheral vasodilator having a direct spasmolytic effect on smooth muscles due to an inhibition of cyclic nucleotide phosphodiesterase thus increasing levels of intracellular cyclic However, it is shown that papaverine preferably inhibits the calmodulin stimulated cyclic AMP-phosphodiesterase a~tivity.~ The spasmolytic effect of papaverine is most pronounced on blood vessels including coronary, cerebral, pulmonary, and peripheral arterie~.~ It has a distinct relaxant effect on smooth muscles of the bronchi, gastrointestinal tract, ureters, and biliary system.6 Papaverine is effectively used in different diseases, such as in cerebrovascular

* Addressee for correspondence. 0142-2782/9 1/070537-10$05.OO 0 1991 by John Wiley & Sons, Ltd.

Received 31 August 1990

538

C. KRAUS ET A L .

and cardiovascular insufficiency, intestinal colics associated with nephrolithiasis and cholecystolithiasis, gastrointestinal spasms and p s o r i a ~ i s .Nowadays ~,~ it is used alone or in combination with phentolamine as an intracavernous injection for the treatment of erectile Only a limited number and little unequivocal data are available on the pharmacokinetic behavior of papaverine HCl after intra- and extravascular administration. It is known that papaverine shows a high variation of bioavailability. Axelrod et al. investigated first the fate of papaverine in man.l0 They showed that papaverine is almost completely metabolized in the liver by 0-demethylation to phenolic compounds. The major metabolite is 4'-hydroxy papaverine. The metabolites are excreted in urine and bile as glucuronide and sulphate conjugates." More than 90 per cent of papaverine is bound to plasma proteins."J2 Ritschel and Hammert3used the data of Axelrod et aZ.I0for a retrospective pharmacokinetic analysis of papaverine plasma levels in man. Further investigations of the pharmacokinetics of papaverine in healthy volunteers were published by Garret et a1.14and by Berg et ~ 1 . ~ ~ The typical animal model for pharmacokinetic studies is the Beagle dog.16 Until now the pharmacokinetic behavior of papaverine HCl has not been well documented in that species. The aim of the present study was to establish the pharmacokinetics of papaverine HCl and to obtain a comparison of the bioavailability upon IV, PO, rectal, vaginal, topical and buccal routes of administration in Beagle dogs.

MATERIALS AND METHOD Experimental design

Eleven healthy Beagle dogs (three female and eight male) with a mean body weight of 10.5 f 2.3 kg (SD) were used to determine the pharmacokinetic profile of papaverine HCl. Six of these dogs were used in a crossover experimental design to compare the pharmacokinetics after IV, PO, rectal and topical administration. After the death of one female dog the vaginal study could be realized with only two remaining female dogs. Five other dogs participated in the buccal absorption study. Blood level concentrations of all 11 dogs were measured after IV administration of papaverine HCl to make an individual calculation of the bioavailability for each dog possible. Whereas the dogs were fasted for the IV, PO, vaginal, topical and buccal study over a period of 12h (overnight fasting), there was a prolonged fasting period over 18h before rectal administration. Water was available ad libitum at all times. The drug was administered between 8 am and 10 am to exclude influences by circadian rhythm.17J8A minimum washout period of 1 week was maintained between the treatments. The dogs were anesthetized by IV injection of sodium pentobarbital (NembutaP 50 mg ml-I; Abbott Laboratories, North Chicago, IL, USA) before vaginal and buccal administration. In preliminary

PAPAVENNE PHARMACOKINETICS

539

experiments we ascertained that the anesthetic did not interfere with the analysis of papaverine HCl. Drug administration Intravenous administration. A dose of 2mg papaverine HCl kg- body weight (Sigma Chemical Co., St Louis, MO, USA) was administered by an IV push injection over 1 min into a cephalic vein. Time zero was considered when 50 per cent of the desired dose was injected. The aqueous solution was sterile. The concentration of the injected drug solution was 7-5mg ml-'. Peroral administration. A hard gelatin capsule (size 00), containing papaverine HCl in a dose of about 5 mg kg-' body weight, was placed on the posterior portion of the tongue, the mouth was closed, and air was blown through the dog's nostrils to induce swallowing. This was followed by 50ml water from a syringe into the mouth for rinse. Rectal administration. A dose of about 5mg papaverine HClkg-' body weight, moleculardispersly distributed in a hydrogel, was administered rectally 50 mm deep into the rectum. The hydrogel consisted of 12.0 per cent Cab-O-Sil (Cabot Co., Boston, MA, USA), 52-8 per cent polyethylene glycol 400 (Sigma Chemical Co., St Louis, MO, USA) and 35.2 per cent Soerensen buffer (Matheson Coleman and Bell Manufacturing Chemists, Norwood, OH, USA) pH 6.2. It was prepared by dissolving papaverine HCl in the aqueous buffer solution and mixing with polyethylene glycol. Cab-O-Sil was added to this solution continuously under stirring. More than 1 per cent of papaverine is unionized as the base in the hydrogel formulation. Vaginal administration. A dose of 5mg papaverine HCl kg-' body weight was dissolved in a hydrogel and administered deeply into the vagina of the anesthetized dog. The composition of the hydrogel was equal to the described formula which was used for rectal treatment. An excretion of the hydrogel was avoided by closing the vagina with an adhesive bandage. Topical administration. After shaving the lateral side of the dog, a siliconbased frame (Silastic" MDX4-4210, Dow Corning Co., Midland, MI, USA) with internal dimensions of 100 X 15Omm was fixed to the skin surface using a medical adhesive (355 Medical Adhesive@Dow Corning Co., Midland, MI, USA). A dose of about 50 mg papaverine HC1kg-I body weight, incorporated in 30g hydrogel, was administered to the skin inside the boundaries of the affixed frame, resulting in a gel application thickness of 2mm. The same hydrogel, the composition of which is described above, was used again for topical administration. Occlusion conditions were maintained by a plastic film, which was placed over the entire surface of the treated skin. After 3 h the hydrogel

540

C.

KRAUS ET A L.

was removed and the skin surface was cleaned with cotton balls moistened with a solution of 60 per cent isopropanol. The papaverine content in the remaining hydrogel was determined to estimate the actually absorbed dose size. Buccal administration. The buccal administration was performed by means of a buccal absorption cell, which is described by Ritschel et The absorption cell was placed on the inside buccal mucosa of an anesthetized dog, and fixed to the cheek with two alligator spring clamps (Parallel Jaw Spring Clip, Model 612-12, Edward Labs, Irvine, CA, USA). Inside the absorption cell the surface of the buccal mucosa was washed with 0.5ml Soerensen buffer solution (pH 6.2) and then the cell was filled with about 0 . 5 d of drug suspension (50 mg papaverine HCl rnl-l). At pH 6.2 more than 1 per cent of the drug molecules are unionized. After 1 h the remaining drug suspension was aspirated, and the cell was rinsed with 05ml Soerensen buffer solution (pH 6.2) 10 times. The actually administered dose size could be determined by analysis of the papaverine content of the aspirated suspension and rinsings. Blood sampling

For the measurement of papaverine concentration, venous blood samples of about 3 ml were taken immediately before as well as at 5, 10, 15, 30, 45, 60, 90, 120, 180, 240, 300 and 360 min after IV and PO administration, at 5, 10, 15, 30, 45, 60, 75, 90, 120, 150, 180, 240 and finally 360 min after buccal administration, at 10, 20, 30, 45, 60, 90, 120, 180, 240, 360, 480, and 600 min after vaginal administration, and at 10, 20, 30, 45, 60, 80, 100, 120, 180, 240, 300, 360, 480, 600 and finally 720 min after rectal and topical administration. The blood was transferred into heparinized glass test tubes (Monoject@Blood Collection Tubes, Sherwood Medical, St Louis, MO, USA) containing 143 units of sodium heparin U.S.P. and centrifuged (CentrificTMCentrifuge, Model 225, Fisher Scientific, Springfield, NJ, USA) at 3000revmin-' for 15 min. The obtained plasma was frozen and stored in plain test tubes until analyzed. Drug analysis

The plasma concentration of papaverine was analyzed by a modified HPLC method described by Pierson et aL20 The HPLC system consisted of a HPLC chromatograph (Programmable Solvent Module 126, System GoldTM,Beckman Instruments, Inc., San Ramon, CA, USA), equipped with a valve injector (50 ~1 loop) (AltrexTMValve Injector, Beckman Instruments, Inc., San Ramon, CA, USA), a microparticulate non-polar reversed phase C18-column(Micro BondapakTM,Waters, Milford, MA, USA), and an UV detector (Scanning Detector Module 167, System GoldTM,Beckman Instruments, Inc., San Ramon, CA, USA), set on 254nm. The system was operated at ambient temperature

541

PAPAVERINE PHARMACOKINETICS

I

h

I1

01 0

c n

0 v)

n

a

T i m e (min)

(a)

Time (min)

(b)

Figure 1 . HPLC chromatograms of dog plasma, spiked with 12.5 pg internal standard (11) ml-' plasma, after dosing with papaverine HCl: (a) papaverine 0.469 pg ml-' (I); (b) papaverine 0.733 pgml-' (I)

with a flow rate of l.8mlmin-'. The mobile phase consisted of 55 per cent (v/v) methanol, 1 per cent (vh) acetic acid (both Fisher Scientific, Springfield, NJ, USA), and 0.005 M 1-heptanesulfonicacid sodium (Sigma Chemical Co., St Louis, MO, USA) ad 100 per cent HPLC-grade distilled water (Fisher Scientific, Springfield, NJ, USA). The plasma was spiked with chlorpheniramine maleate (Sigma Chemical Co., St Louis, MO, USA) 12.5pg ml-' as an internal standard. Quality parameters of the HPLC analysis are: reproducibility: CV = 1-5-2-0per cent r = 0.99994 linearity: recovery: 98 per cent Figure 1 shows typical HPLC chromatograms of two plasma samples. The ratio of the peak height of papaverine HC1 to that of the internal standard was used to calculate the drug concentration, based on a linear standard curve. Extraction procedure

Exactly 1.00 ml plasma was spiked with 0.25ml of an aqueous solution of chlorpheniramine maleate (5Opgml-') and vortexed; 0.2ml of 0.7 N NaOH and 10.0 ml ether (Fisher Scientific, Springfield, NJ, USA) were added. T h e sample was shaken mechanically for 15 min and centrifuged. The ether phase was extracted with 0.50ml of O.3NHCl by shaking and centrifuging as described

542

C . KRAUS ET A L .

above. The ether phase was evaporated, and 5 0 ~ of 1 the remaining aqueous phase was injected into the HPLC chromatograph. Pharmacokinetic analysis

The pharmacokinetic parameters were evaluated using a curve fitting computer program, the RESID method,21for the data of IV and PO administration, and a compartment model independent computer program, the AUC-RPP method,22for the data of rectal, vaginal, topical and buccal administration, respectively. RESULTS AND DISCUSSION The plasma concentration-time curves for all routes of administration are shown for the individual dogs in Figure 2. The semilogarithmicplots of the plasma concentrations of papaverine against time after IV and PO administration showed that papaverine pharmacokinetics are best described by an open two-compartment mode. The duration of the distribution phase was about 45-60min after IV administration, and 1-2h after PO administration, respectively. The peak plasma concentration occurred between 0.25 and 1 h after PO administration, between 2 and 4h after rectal, and 1h after vaginal administration. A uniform peak time after topical administration was not ascertainable. Also, after buccal administration a distinct peak time was not detectable. This fact showed the presence of a slow absorption process with the absorption rate as the rate-limiting step. A flip-flop model results. However, a distinct lag time of absorption was not observed for any route of administration investigated. The pharmacokinetic parameters of papaverine HCl were derived by RESID and AUC-RPP computer evaluations. They are listed in Table 1 as mean values with their corresponding standard deviations. After IV administration the terminal disposition rate constant, /3, varied between 0.29 and 0.43 h-* (elimination half-life 1.62.4h). The distribution rate constant, a , ranged from 2.07 to 4.30h-1 (half-life of distribution 1&20 min). The plasma levels after IV and PO administration did not show a significant difference of the elimination rate constant. The absorption rate constant after PO and vaginal administration, k,, was 10.77 and 9.84hP1,respectively. After both applications tlhawas about 5 min. In comparison with this, the absorption rate constant after rectal administration was lower, it was 2.04h-I ( t H a= 25 min). Because of the presence of a flip-flop model, the absorption rate constant after buccal administration would have been seen to be derived from the terminal slope of the plasma level curve. Since the plasma concentrations were very low, the sensitivity of the HPLC assay was insufficient to determine the concentration during the elimination

543

PAPAVERINE PHARMACOKINETICS

0

2

4

60

2

4

6

8

10

12

Time [h] Figure 2. Papaverine plasma concentration-time profiles upon IV, PO, rectal, vaginal, topical, and buccal routes of administration of papaverine HCI

phase. Therefore, the absorption rate constant was not determined after buccal administration. After IV administration the volume of the central compartment, V,, at steady

t, a

454-70.0 0.57 f 0.20

18.1-33.3 1.oo

(mg)

(mg)

D

Dw

41.6-68.4 0.25f0.11

*

8.0-17.0

0.91 f0.38 5.99 f 3.60

1 176.5 f 559.0 107.3 f 52.3 6.21 f 1.23

n.d.: Not determined. * By curve-fitted program RESID. By compartment model independent program AUC-RPP. For extravascular route of administration Vd and CI are listed for V,/fand ClV IV data used.

f,PP

f

8.0-15.0

9.0-17.0

(kg)

BW

1.94 f0.62 4.78 f 2.00

1.54f0.15 3.52 f 0.64

( w h m1-l) (pg.h2 ml-I)

AUC,,,, AUMC,,,,,

(ml.kgmin-I)

(h)

440.2 f 144.8 42.8 f 19.0 2.45 f 0.61

229.8 f 61.3 21.8 f 2.25 2.28 f0.33

(ml min-l)

n.d. n.d. 18.9 f9.99

n.d. n.d. 7.49 f4-07

C1' c1t MRT

v*D*

vdss

n.d. n.d. 2.04 f 1.27 0.42 f0.18

0 6

Rectalt

0.41 f 0.09 1.80 f 0.48 4.94 f 2.07 0.16 f0.08 10.8 f4.43 0.08 f 0.06

PO*

1.30 f0 3 2 3.01 f 0.52 3.93 f 0.54

(h)

tlha

0.34 f 0.04 2.09 f0.24 3.16 f 0.77 0.23 f0.06

IV*

(1 kg-') (1 kg) (1 kg-V

(h-9

k,

vc

(h)

t,,

0-9

(h-7

(h)

B

Pharmacokinetic parameter

204-75.7 0.40 f0.24

4964-603.4 0.03 f 0.02

524k53.0 0.53 f0.15 24.7-39.9 0.87 f0.04

10.5-18.0

1.10 k0.34 8.79 f4.95 10.5-1 1.0

1.97 f0.61 9.67 f 2.41

87550 f 2380.2 815.3 f 322.6 7.59 f 1.87

n.d. n.d. 142.7 f56.2

n.d. n.d. 10.3 f 3.91

464.6 f 138.1 43.5 f 14.3 4.95 f0.31

n.d. n.d. n.d. n.d.

6 6

Topicalt

n.d. n.d. 9.84 f 5.61 0.08 f 0.05

6 8

Vaginalt

21.3-56.8 0.08 f0.04

21.3-56.8 0.08 f 0.04

9.0-1 2.0

0.18 f0.04 0.87*0.16

2433.3 f 5 17.7 250.1 f 66.4 4.93 f 0.54

*

n.d. n.d. 46.70 11.2

n.d. n.d. n.d. n.d.

6 8

Buccalt

Table 1. Pharmacokinetic parameters of papaverine HCl following different routes of administration (X f SD; n = 6, for vaginal administration n = 2)

545

PAPAVERINE PHARMACOKINETICS

state, V,, and the apparent volume of distribution, V4, were 1.30 1 kg-l, 3.01 1 kg-l and 3.93 1 kg-', respectively. The total clearance C1, was 21-8 mbkg min-I. For the extravascular routes of administration the values of Vd and C1 are listed for Vdlfand Cl$ The absolute bioavailability,f, after extravascular routes of administration was determined from the total area under the curve, AUC,,v,+,, and administered dose size, D, in comparison with these values, measured after IV administration. The application of different dose sizes was possible because no dose dependency was observed. The mean bioavailability data which are listed in Table 1 were derived from individual calculations for each dog. For papaverine HCl there was an absolute bioavailability determined of 57.2 per cent, 25.2 per cent, 53.2 per cent, 3.2 per cent and 7.5 per cent, respectively, after PO, rectal, vaginal, topical and buccal administration. The determined absolute bioavailability of 57.2 per cent after PO administration in Beagle dogs has an almost equal value to that reported in man.I3 This shows that the Beagle dog is a good model for pharmacokinetics of papaverine HCl in man. For vaginal and topical administration the listed values of the absolute apparent bioavailability,fapp,were derived from respective, corrected doses. These dose sizes were based on the actual absorbed amount of drug, which were obtained from the difference between administered dose size and recovered amount of drug after administration. It is an apparent bioavailability because the actual absorbed dose depends on the special experimental design, i.e. the used skin area for the hydrogel administration, the thickness of the hydrogel layer on the skin, the period of drug administration, and the dimensions of the buccal absorption cell. The high apparent bioavailability of papaverine HCl after vaginal administration (f,,, = 87.4 per cent) was remarkable. Table 2. Mean absolute bioavailability and mean apparent absolute bioavailability of papaverine HCl upon different routes of administration based on the data of the AUC up to a certain time Bioavailability basedon AUC,,,

f I.V. P.O. Rectal Vaginal

Topical Buccal

1-00 0-57 0.25 0.53 0.032 0.075

,af

Bioavailability basedon AUC,,,,,

f

fam

Bioavailability basedonAUCo,,,,,

f

1.oo

1.00

1.oo

0.57 0.25 0-87

0.57

0.57

1.00 -

-

0.21

0404

-

-

0.50 0.028

0.075

0.059

0.059

-

faPP

1.oo 0.21 0.81 0.292 -

The AUC,,-+, which were calculated from the concentration-time data after topical and buccal administration might be underestimated because the elimination phase was not reached at the end of the observed time period. The sensitivity

546

C . KRAUS ET A L .

of the papaverine analysis limited the evaluation of the more blood samples over a longer period of time. Therefore, in addition to the calculated bioavailability based on the AUCO,,, Table 2 shows the bioavailability values, which were derived from certain AUCo+t.These data were obtained from a comparison of the AUCo,, over a time period of 6 h for PO and buccal administration and 12 h for rectal, vaginal and topical administration, respectively. This calculation, which was based on a comparison of the AUCo-,, made an accurate determination and comparison of the bioavailability possible. After taking the AUCo., as the basis for the calculation of the bioavailability, the apparent absolute bioavailability upon different routes of administration decreased in the order vaginal, PO, topical, rectal and buccal administration.

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Profile of Papaverine Hydrochloride, K. Florey (Ed.), Academic Press, New York, 1988, pp. 36747. G. Poch and W. R. Kukovetz, Life Sci., 10, 133 (1971). G. Poch and W. Umfahrer, Naunyn-Schmiedebergs Arch. Pharmacol., 293,257 (1976). R. Mannhold, Arzneim. Forsch., 38, 1806 (1988). F. H. Stern, J. Amer. Geriat. Sac., 18, 507 (1970). M. A. Stawiski, J. A. Powell, P. G. Lang, A. Schork, E. A. Duell, and J. J. Voorhees, J. Invest. Dermatol., 64, 124 (1975). G. K. McEvoy (Ed.) AHFS Drug Information, American Society of Hospital Pharmacists, Inc., Bethesda, Maryland, 1989, pp. 941-942. R . Virag, D. Frydman, M. Legman and H. Virag, Angiology, 35,79 (1984). T. C. Gasser, R. M. Roach, E. H. Larsen, P. 0. Madsen and R. C. Bruskewitz, J. Urol., 137,678 (1987). J. Axelrod, R. Shofer, J. K. Inscoe, W. M. King and A. Sjoerdsma, J. Pharmacol. Exp. Ther., 124,9 (1958). F. M. Belpaire and M. G. Bogaert, Xenobiotica, 5,421 (1975). F. M. Belpaire, M. G. Bogaert and M. M. Mussche, Eur. J. Clin. Pharmacol., 11,27 (1977). W. A. Ritschel and G. V. Hammer, Int. J. Clin.Pharmacol., 15,227 (1977). E. R. Garret, H. Roseboom, J. R. Green Jr. and W. Schuermann, Int. J. Clin. Pharmacol., 16,193 (1978). G. Berg, K.-A. Jonsson, M. Hammar and B. Norlander, Pharmacol. Toxicol., 62,308 (1988). W. A. Ritschel, Sci. Techn. Prat. Pharm. (Paris), 3, 125 (1987). W. A. Ritschel, Oesterreich. Apoth. Ztg., 37, I (1983). W.A. Ritschel, Pharm. Internat.,5, 116(1984). W. A. Ritschel, M. Neub and D. D. Denson, Meth. Find. Exptl. Clin. Pharmacol., 9, 811 (1987). S. L. Pierson, J. J. Hanigan, R. E. Taylor and J. E. McClurg, J. Pharm. Sci., 68, 1550 (1979). W. A. Ritschel, RESID: A curve-fitting program to generate pharmacokinetic parameters, in International Symposium in Clinical Pharmacokinetics, Salzgitter-Ringelheim, July 20-21, 1975. W. A. Ritschel, Meth. Find. Expt. Clin. Pharmacol., 8,633 (1986).