J. Vet. Med. A. 42, 397-409 (1995) @ 1995 Blackwell Wissenschafts - Verlag, Berlin ISSN 0931-184X

Clinic of Small Animals, Hanover School of Veterinary Medicine

Long-Term Treatment of Diseased, FIV-Seropositive Field Cats with Azidothymidine (AZT)

S. HART and I. NOLTE

Address of authors: Clinic of Small Animals, Hanover School of Veterinary Medicine, Bischofsholer Damm 15, D-30173 Hannover, Germany

With 5 figures and 4 tables

(Received for publication March 25, 1995)

Summary The long-term effectiveness of Azidothymidine (AZT, Zidovudine) was evaluated in FIV-

seropositive cats with clinical symptoms (n = 9; Group 1) compared with conventional symp- tomatical therapy (n = 5; Group 2). The oral administration of Azidothymidine at a dosage of 5 mg/kg BW yielded a mean peak plasma concentration of 4.59 pM one hour after application (median: 3.74 pM). Elimination half time was 1.5 h.

The permanent oral application of Azidothymidine at a dosage of 5 mg/kg BW TID led to a total recovery from clinical symptoms in six of nine FIV-seropositive cats (Group 1) 4-6 weeks after the onset of therapy. One cat clinically improved with only sporadical recurrence of disease; therapy with Azidothymidine was not effective in two cats.

All the FIV-seropositive cats treated symptomatically responded well to antibiotics and immunomodulators within 1C-14 days (n = 5; Group 2). Recurrence of clinical symptoms was noticed in three of five patients within 2 years after therapy and one cat died.

During the treatment with Azidothymidine hyperproteinemia and abnormal albumin-to- globulin ratio became normal within 6 months in four FIV positive cats (Group I), whereas hyperproteinemia did not change in Group 2. The following adverse effects were noticed in Group 1: a transient decrease of red blood cell count (RBC), packed cell volume (PCV) and haemoglobin until the 4th week of application of Azidothymidine (5/8), but the haemogram was within the normal range after 3 months. In one cat with hyperglycemia the anaemia remained until the administration of Azidothymidine was terminated. Heinz (Schmauch) bodies in the erythrocytes appeared in two FIV-positive cats 2 weeks after the onset of the therapy.

Introduction Since the detection of the Feline Immunodeficiency Virus (FIV) reports o n

treatment of sick cats have been rare. In vitro studies show a decrease in the FIV reverse transcriptase (RT) activity after application of RT inhibitors (NORTH et al., 1989). Two of these drugs (Azidothymidine, AZT, Zidovudine and PMEA, Phos- phonomethoxyethyladenine) were first tested for their efficacy to inhibit the FIV life cycle. Several clinical studies reported that FIV-seropositive, sick cats clinically improved after subcutaneous administration of the drugs for 3 t o 4 weeks (EGBERINK et al., 1990; EGBERINK et d., 1991; HARTMANN et al., 1992).

US. Copyright Clearance Center Code Statement: 0931 - 184X/95 /4206 - 0397$11.00/0

398 HART and NOLTE

Because of the risk of progression of the disease temporary administration of reverse transcriptase inhibitors does not seem to be recommendable in FIV-seropositive cats with chronic diseases. Until now, n o data about clinical course, survival and adverse effects after long-term administration of RT inhibitors are available in cats with FIV infection. F o r a long-term regimen of Azidothymidine or other RT inhibitors the oral route of administration would be preferable to the parenteral application. This study was initiated t o determine an optimal dosage of Azidothymidine for oral administration confirmed by pharmacokinetic studies. The main purpose was to evaluate the long-term effectiveness of the oral administration of Azidothymidine in FIV-positive cats with clinical symptoms, compared with symptomatically treated FIV-positive cats. Furthermore, the course of the disease and possible adverse reactions were recorded during the application of Azidothymidine.

Materials and Methods Elimination half time

Studies to determine elimination half time (t1I2) were performed in six sick, FIV-seropo- sitive, naturally infected cats (two males, two neutered males and two females) with a body weight of 4.1 k 0.9 kg and an age of 4.8 2 1.5 years. They were fed a commercial cat food (Whiskas, Effem, Verden, Germany) and they had tap water ad libitum. The animals were hospitalized for at least 3 days until the study started. The afternoon prior to and during the study the cats were left without food, but they had water ad libitum. Blood was taken 1-4, 6 and 8 hours after administrating Azidothymidine from the cephalic or jugular vein in glass tubes. After centrifugation of the blood for 10 min at 1500 g, serum was stored at -70 "C. Serum levels of Azidothymidine were measured by high-performance liquid chromatography (HPLC) within one week after collection (KAMALI and RAWLINS, 1990).

Therapy group Naturally infected cats with clinical signs of FIV infection (n = 14) were presented by the

owners or referred to the clinic. All patients were ELISA- and Western Blot-positive for the FIV infection and negative for FeLV antigen. ELISA tests were performed using a commercial test kit (CITE ComboR, IDEXX Lab., Westbrook, ME, USA).

Study design FIV-seropositive cats with clinical symptoms were randomly assigned to one of two

treatment groups. Group 1 (n = 9 cats) received Azidothymidine (RetrovirR, Wellcome, Burgwedel, Germany) at a dosage of 5 mg/kg BW TID for 3 months or longer. Azidothymidine was usually administered as monotherapy; only if necessary, additional symptomatic treatment (antibiotics (penicillin, amoxicillin) for 1 week (n = 2), local disinfection (I), fluid therapy IV and penis amputation in a case of recurring FUS) was done in four FIV-positive cats (Table 1). FIV-positive cats of Group 2 (n = 5) were treated only symptomatically depending on the concurrent disease, i.e. with antibiotics (Spiramycin, Enrofloxacin, Lincomycin etc.), immu- nomodulators (Orfvirus, Bayparnun@, Bayer, Leverkusen, Germany) and fluid therapy.

Clinical assessment The FIV-seropositive sick cats underwent intense clinical and laboratory examination prior

to therapy and then 2 and 4 weeks, 3, 6, 9 and 12 months after the onset of Azidothymidine application. Besides general condition, body weight and appetite, mouth, lymph nodes, hair coat and respiratory tract were examined with special attention. Haematological and biochemical tests as well as a FIV test 3 months after the onset of the treatment completed the control.

Laboratory evaluation Haematologic examination included determination of complete red blood cell counts,

differential white blood cell counts, haematocrit, haemoglobin, platelet and reticulocyte counts. RBC and haemoglobin concentration were measured with a semi-automated counter (Micro- cellcounter F-800, Sysmex Digitana, Hamburg, Germany) according to the manufacturer's advice. Leucocytes, reticulocytes and platelets were counted visually (HALLMANN, 1980; HART

Treatment of FIV-Seropositive Field Cats 399

and NOLTE, 1990). Packed cell volume was measured using the microhaematocrit-centrifugation method. Reticulocytes and Heinz bodies were counted on brilliant cresyl blue-stained smears. Blood chemistry (alanine aminotransferase (ALT), glutamic dehydrogenase (GLDH), total bilirubin, blood urea nitrogen (BUN), creatinine, total protein, glucose, total calcium) was performed by use of an automatic chemical analyzer (Hitachi 704, Boehringer Mannheim, Mannheim, Germany). Sodium and potassium were measured by use of an automatic analyzer with ion-sensitive electrodes (Ciba Corning 614, Ciba Corning, Fernwald, Reiskirchen, Germany). Serum celluloseacetate electrophoresis was accomplished in an Elphor chamber (Bender & Hobein, Munich, Germany) at 220 V for 20 min with a power device (Pherostab.500, Biotec-Fischer, Reiskirchen, Germany). After dying with amidoblack the bands were measured densitometrically (Elphorgraph 3, HBE, Neubiberg, Germany). The albumin-to-globulin (AG) ratio was calculated from the appropriate data.

Adverse events Adverse events in association with the oral administration of Azidothymidine were recorded

by the clinician.

Statistics Data were expressed as means, standard deviations (SD) and medians for all results. For

statistical reasons results of a third group (FIV-seropositive cats with successful Azidothymidine therapy) were shown as well. The haematological and biochemical data before and during the treatment were compared for each group with the paired-samples Wilcoxon signed rank test. Differences between the groups were evaluated with the Mann-Whitney test (SHO~T, 1991). P-values < 0.05 were considered significant.

Plasma levels of Azidothymidine were given by mean, standard deviation and median. Pharmacokinetic evaluation was performed with the statistical program Plotit 2.0 using a non- linear regression according to a Marquardt algorithm based on the means of the plasma levels.

Elimination half time (tlJ was calculated according to the formula In 2

t l I 2 = - b '

Results Elimination half time

Azidothymidine given orally at a dose of 5 mg/kg BW in six cats peaked in a mean plasma level of 4.59 pM (median: 3.74 pM) one hour after application. Mean plasma concentration after 8 h was 0.23 pM. Elimination half time was 1.5 h (Fig. 1).

Treatment Results Complete improvement of clinical signs occurred in six out of nine FIV-sero-

positive cats treated with Azidothymidine (Group 1) (Table 1). Within 4 to 8 weeks gingivitis, lymphadenopathy and symptoms of the upper respiratory tract disappeared (n = 5). Dull hair in two FIV-infected cats became bright and shiny 6-8 weeks after the onset of Azidothymidine treatment.

In one cat (# 6) suffering from pneumonia, considerable improvement was seen, and the symptoms reoccurred only sporadically. One patient (cat 9) with initial complete recovery displayed a changing health condition 5 months later. A liver tumor was sonographically diagnosed in this patient and the cat was euthanized. Treatment with Azidothymidine for 3 months was unsuccessful in one FIV-positive cat with proliferative gingivitis (# 4).

At present, 6 FIV-seropositive cats have been treated with Azidothymidine for at least 9 months, and up to 2 years (Table 1). With the exception of one patient (cat 6) no recurrence of symptoms after beginning the application of Azidothymidine has been noticed.

Clinical recovery occurred in all the FIV-seropositive cats of Group 2 after 10-

400

10

9 1

HART and NOLTE

n = 6 cats

1 2 3 4 5 6 7 8 9 10 Time [hl after AZT administration

0 5 mg/kg BWp.0.

Fig. 1. Plasma concentration of Azidothymidine after oral administration of 5 mg/kg BW (mean and standard deviation).

14 days of symptomatic therapy depending on the severity of disease. The patients responded well to antibiotics combined with immunomodulators (Table 2). Recurrence of clinical signs was noticed in three of five FIV-seropositive cats within 2 years after symptomatic therapy (Group 2). Two of three patients repeatedly suffered from the disease and one cat died. Elevated white blood cell counts became normal after 2 weeks of therapy in all groups.

In four FIV-seropositive cats with hyperproteinemia (Group 1) the total protein decreased to the normal range after treatment with Azidothymidine for 6 months although differences were not statistically significant (p = .076) (Fig. 2). Simul- taneously the elevated gamma-globulin fraction decreased, and the altered albumin- to-globulin ratio became normal (Table 3). The elevated total protein concentration of FIV-seropositive cats in Group 2 (n = 3) remained above reference range and the abnormal albumin-to-globulin ratio did not improve.

All the other parameters of clinical biochemistry, even liver enzymes and total bilirubin, were not affected by the treatment with Azidothymidine at a dosage of 5 mg/kg BW TID orally. Also, cats with symptomatic therapy alone (Group 2) did not show any noticeable changes in their biochemical data.

All the nine cats of Group 1 remained FIV-positive 3 months after the onset of the Azidothymidine treatment.

Adverse effects of azidothymidine During the application of Azidothymidine a significant decline of the red blood

cell count (RBC) (week 2: p = 0.036; week 4: p = 0.012), packed cell volume (PCV) (week 2: p = 0.12; week 4: p = 0.018) and haemoglobin (week 2: p = 0.21; week 4: p = 0.025) was seen in the successfully treated cats of Group 1 which started after 2 weeks and got worse until the 4th week of application (Fig. 3). Two months later

Tabl

e 1.

Eff

ect

of t

he tr

eatm

ent

with

Azi

doth

ymid

ine

on th

e cl

inic

al s

tatu

s of

FIV

-ser

opos

itive

cat

s

Clin

ical

sym

ptom

s pr

ior

to

Out

com

e du

ring

A

dditi

onal

s

mpt

omat

ical

l

Cat

A

ge

Dur

atio

n of

A

zido

thym

idin

e A

zido

thym

idin

e no

. [y

ears

] B

reed

G

ende

r di

seas

e tre

atm

ent

treat

men

t T

ime

of f

ollo

w-u

p t

erap

y

1 4

ESH

m

ale,

neu

tere

d

2 4

ESH

fe

mal

e,

3 4

ESH

m

ale,

neu

tere

d

4 2

Siam

ese

mal

e,

5 10

E

SH

fem

ale,

neut

ered

neut

ered

neut

ered

6 12

E

SH

mal

e

7 5

ESH

m

ale

3 w

eeks

6 w

eeks

-

seve

ral w

eeks

1 ye

ar

4 w

eeks

4 da

ys

diar

rhea

, vo

miti

ng,

wei

ght

loss

al

opec

ia, c

rust

y de

rmat

itis

puru

lent

derm

atiti

s

prol

ifera

tive

ging

iviti

s up

per

resp

irato

ry

sign

s,

h ype

rgly

cem

ia

coug

h, p

neum

onia

recu

rrin

g FU

S,

cyst

itis

wei

ght

gain

, tot

al

reco

very

tota

l rec

over

y

tota

l re

cove

ry

unsu

cces

sful

tota

l rec

over

y

reco

very

, bu

t sp

orad

ical

cou

gh-

tota

l rec

over

y af

ter

surg

ery

ing

2 ye

ars

afte

r 5 m

onth

s lo

st

2 ye

ars

loca

l

2 m

onth

s

to fo

llow

-up

disi

nfec

tion

term

inat

ion

of

Azi

doth

ymid

ine

appl

icat

ion

afte

r 5

mon

ths

2.5

year

s

22 m

onth

s

8 4

ESH

m

ale

3 w

eeks

up

per

resp

irato

ry

tota

l re

cove

ry

18 m

onth

s

9 6

ESH

m

ale,

neu

tere

d -

apat

\y , w

eigh

t in

itial

rec

over

y eu

than

asia

afte

r

sign

s,

lym

had

enop

athy

loss

, dul

l hai

r coa

t, gi

ngiv

itis

of l

iver

tum

or

5 m

onth

s be

caus

e

amox

icill

in a

nd

clav

ulan

ic a

cid

for 7

days

pe

nici

lline

, flu

id t

hera

py,

amm

oniu

m

chlo

ride,

die

t, 2n

d tim

e pe

nis

ampu

tatio

n,

enro

floxa

cine

P m

n

A p.

P 2

ESH

= E

urop

ean

Shor

thai

r cat

P 0

h,

Tabl

e 2.

Eff

ect o

f the

sym

ptom

atic

al th

erap

y on

the

clin

ical

sta

tus

of F

IV-s

erop

ositi

ve c

ats

Cat

A

ge

Dur

atio

n of

C

linic

al

Tim

e of

no

. [y

ears

] B

reed

G

ende

r di

seas

e sy

mpt

oms

The

rapy

fo

llow

-up

Out

com

e

1 4

ESH

m

ale,

2 5

ESH

fe

mal

e ne

uter

ed

3 3

ESH

fe

mal

e

4 3

ESH

m

ale,

ne

uter

ed

5 7

ESH

fe

mal

e,

neut

ered

1 w

eek

neck

abs

cess

4 da

ys

ocul

ar

disc

harg

e, d

ysp-

ne

a

resp

irato

ry s

igns

se

vera

l day

s up

per

3 w

eeks

di

arrh

ea,

wei

ght

loss

, ly

mph

aden

opat

hy

4 da

ys

feve

r, an

orex

ia

antib

iotic

, lo

cal

2.3

year

s di

sinf

ectio

n an

tibio

tic,

3 ye

ars

imm

unom

odul

ator

antib

iotic

, 1.

5 ye

ars

opht

halm

ic

oint

men

t, im

mun

o-

mod

ulat

or

fluid

ther

apy,

ant

i- 1

year

bi

otic

, st

yptic

a,

imm

unom

odul

ator

an

tibio

tic,

13

imm

unom

odul

ator

m

onth

s

2 ye

ars

late

r sk

in a

bsce

ss

2 ye

ars

late

r di

scha

rge,

dy

spne

a, p

rolif

erat

ive

stom

atiti

s no

ne

afte

r 6 m

onth

s di

arrh

ea 1

ye

ar l

ater

dia

rrhe

a,

urem

ia,

euth

anas

ia

none

ESH

= E

urop

ean

Shor

thai

r cat

2 g To

tal p

rote

in [

g/dl

] A

lbum

in [

%I

y-gl

obul

in [

%]

2l

Prio

r to

Azi

- A

fter 6

mon

ths

Prio

r to

Azi

- A

fter 6

mon

ths

Prio

r to

Azi

- A

fter 6

mon

ths

z C

at

doth

ymid

ine

of A

zido

thym

- do

thym

idin

e of

Azi

doth

ym-

doth

ymid

ine

of A

zido

thym

- wl 5 E

Tabl

e 3.

Inf

luen

ce o

f th

e tr

eatm

ent w

ith A

zido

thym

idin

e on

tota

l pro

tein

, al

bum

in a

nd y

-glo

bulin

in

4 FI

V-s

erop

ositi

ve c

ats

0

No.

tre

atm

ent

idin

e th

erap

y tre

atm

ent

idin

e th

erap

y tre

atm

ent

idin

e th

erap

y a

3 9.

47

8.37

31

.4

52.5

31

.3

23.6

s.

7.28

6.

98

44.5

48

.0

35.5

24

.5

z.

6 8 8.

78

7.34

26

.7

44.0

37

.4

30.9

TJ

1 9.

18

7.13

33

.1

49.9

47

.0

35.3

z.

0

P 0

W

404

12 11 l o - 9 -

8- c 7 -

6 -

- I

.- 0

: 5 - - m g 4 -

3 - 2 - 1 -

0

HART and NOLTE

-

2

-

4 ...._._._._......-. -.----4 --.---..- .._...__---_-_ _.... ....--

- _._.... --

T T I 8.0 .-- .----- ..._._.__._. ......_....__..... - . - F L

a 6.0 2

m

I I I I I I

I Group 1 * Group2 I Fig. 2. Concentration of total protein of FIV-seropositive cats during treatment (median and

range).

RBC, haematocrit and haemoglobin concentration were again within the normal range (Table 4).

At the end of the treatment period the concentration of haemoglobin was sig- nificantly higher (p = 0.047) in FIV-positive cats with successful Azidothymidine treatment compared with the controls.

Reticulocyte counts diminished only slightly during the observation interval. No significant differences could be seen in the haemogram of the FIV-positive cats after symptomatic therapy (Group 2).

* * 0.01cp<0.05 -1 48 I

* I *

0 0 0.5 1 3 6 9

Time of azidothymidine therapy [months]

0 Erythrocytes (Grp 1) A Erythrocytes (Grp 2)

* PCV (Grp 1)

Fig. 3. RBC and PCV of FIV-seropositive cats during the treatment (median and range).

Tabl

e 4.

Hae

mog

ram

s of

FIV

-ser

opos

itive

cat

s w

ith A

zido

thym

idin

e th

erap

y an

d sy

mpt

omat

ical

trea

tmen

t

Prio

r to

2

Wee

ks

4 W

eeks

3

Mon

ths

6 M

onth

s 9

Mon

ths

Azi

doth

ymid

ine

trea

tmen

t af

ter

the

onse

t of

the

Azi

doth

ymid

ine

trea

tmen

t

Med

ian

Ran

ge

Med

ian

Ran

ge

Med

ian

Ran

ge

Med

ian

Ran

ge

~ ~~

~

Gro

up I

: FIV

-ser

opos

itive

cat

s w

ith A

zido

thym

idin

e th

erap

y N

o. o

f ca

ts

8 8

RB

C [M

ill. /

PI]

9.10

3.

26

7.48

5.

51

6.45

Hae

mat

ocri

t [%

I 37

.5

14

34

18

30.5

T

otal

pro

tein

[g/

dl]

8.84

3.

38

8.78

1.

88

8.46

G

roup

Ia:

FIV

-ser

opos

itive

cat

s w

ith s

ucce

ssfu

l Azi

doth

ymid

ine

ther

apy

No.

of

cats

5

5 R

BC

[Mill

. /PI

] 8.

91

3.26

6.

27

5.51

5.

78

Hae

rnog

lobi

n [g

/dl]

13

.4

4.4

10.2

6.

6 10

.7

Hae

mat

ocri

t [Y

O]

37

7 27

17

30

T

otal

pro

tein

[g/

dl]

8.84

3.

38

8.78

1.

88

8.46

G

roup

11:

FIV

-ser

opos

itive

cat

s w

ith s

ympt

omat

ical

tre

atm

ent

No.

of

cats

5

5 R

BC

[M

ill. /P

I] 7.

76

2.86

8.

03

4.08

7.

84

Hae

mog

lobi

n [g

/dl]

11

.7

3.6

12.4

6.

3 11

.6

Hae

mat

ocri

t [%

I 35

12

37

18

33

.5

Tota

l pro

tein

[g/

dl]

9.00

4.

25

9.50

2.

59

8.93

Hae

mog

lobi

n [g

/dl]

13

.4

5.0

12.0

7.

4 11

.0

8 5.

22

9.0

28

1.84

5 5.

22

7.5

21

1.84

5 0.

67

0.8 3 1.34

7 7.

40

2.92

13

.3

3.3

37.0

9

8.16

1.

85

5 7.

40

1.17

13

.3

2.2

37

6 8.

32

1.55

5 7.

13

4.55

11

.8

6.7

31

16

8.64

2.

73

Med

ia

Ran

ge

Med

ian

Ran

ge

2 c 2 5

5 z

7.20

2.

48

7.66

4.

07

4

13.0

2.

5 13

.4

2.24

z ::

37.0

11

36

.0

8

a %.

7.20

2.

48

7.66

4.

07

n z! 1

n

c WJ

7.72

1.

04

7.72

1.

19

5 5

'D c.

13.0

2.

5 13

.4

2.24

37

11

36

8

7.72

1.

04

7.72

1.

19

5 5

7.22

4.

56

7.82

3.

36

a

11.2

6.

1 11

.9

4.1

32

17

34

10

8.74

3.

17

8.91

3.

06

406 HART and NOLTE

Fig. 4. Punctate and aggregate reticulocytes and several erythrocytes with periphcral Heinz Bodies. Blood smear, Brillant Cresyl Blue stain, 250 x magnification.

In 2 patients (# 1, 7) of Group 1 Heinz (Schmauch) bodies were demonstrable in the erythrocytes after the first 2 weeks of the application of Azidothymidine (Fig. 4). Although the cats were in a healthy condition the Heinz bodies persisted during the treatment.

In one FIV-seropositive cat with a persistent hyperglycemia (# 5 ) a progressive decline of PCV, RBC and haemoglobin concentration was noticed during a 5 month application of Azidothymidine. After the termination of its administration the hae- mogram became normal within one month (Fig. 5).

Discussion In this study, Azidothymidine was administered at a dosage of 5 mgikg BW TID

orally, because the plasma levels suggested a safer RT-inhibition of the FIV than a single dose. The elimination half time of 1.5 h for Azidothymidine corresponded with other reports (1.6 h), where the drug was used at a dosage of 20 mg/kg BW TID orally for the treatment of FeLV-infected cats (ZEIDNER et al., 1990).

Data concerning the effectiveness of inhibition of the FIV life cycle, measured by the activity of RT in vitro, are variable in the literature. 0.05 pM are sufficient to

Treatment of FIV-Seropositive Field Cats 407

- - - - - - - - - - -

2

1

52 48 44 40 36 32 28 24 20 16 '2

- 8 - 4

t application of Azidothymidine

I I I I I I 0' I I I I '0 0 0.5 1 3 5 6

time [months]

-e- Erythrocytes -I- PCV

Fig. 5. Atypical decline of RBC and PCV in a FIV-positive cat with hyperglycemia during the therapy with Azidothymidine.

reduce the RT-activity of FIV-infected thymocytes by 50 percent (EGBERLINK et al., 1990; EGBERINK et al., 1991). NORTH and coworkers (1989) reported that 0.1 pM Azidothymidine inhibited the RT-activity in Crandell feline Kidney cells 14 days p. inf. about 90 percent, but there was only a 15-20 percent inhibition after 21 and 28 days p.inf.

Inhibitors of the RT have proven their ability to stop the FIV life cycle in in vitro- tests and in clinical studies (NORTH et al., 1989; EGBERINK et al., 1990; EGBERINK et al., 1991; HARTMANN et al., 1992). However, the application of Azidothymidine for a limited time may lead to a recurrence of the disease some months later (EGBERINK et al., 1990; EGBERINK et al., 1991). In this study, no recurrence of symptoms was noticed in Group 1, whereas three of five FIV-seropositive cats with symptomatic therapy showed repeated episodes of disease. Moreover, the decrease of the hy- perproteinemia to the normal range and the correction of the abnormal AG ratio after 6 months of administration seems to be a beneficial effect of Azidothymidine. These phenomena indicate a restitution of the impaired function of B-lymphocytes.

Anaemia and bone marrow suppression, which also occur in HIV-infected humans during the application of Azidothymidine, is dose dependent in cats (HASCHEK et al., 1990; REMINGTON et al., 1991). The investigators reported on a progressive anaemia and neutropenia in FeLV-positive cats treated with 10 and 20mg/kg BW Azi- dothymidine for 32 to 34 days (HASCHEK et al., 1990). Another study noticed a decrease of WBC by 48 percent during an application of Azidothymidine for 10 weeks in FeLV-infected cats (20 mg/kg TID P.o.), which became normal 14 days after the end of the medication (ZEIDNER et al., 1990). HARTMANN et al. (1992) also demonstrated the decrease of haematocrit and haemoglobin concentrations during the application of Azidothymidine (5 mg/kg subcutaneous BID) for 3 weeks in FIV-infected cats. They also mentioned the increase of these haematologic parameters in cats assigned to Azidothymidine for longer than 3 weeks, which is confirmed in the present study. The transient impairment of the haemogram during the administration of the drug

408 HART and NOLTE

should be the cause for a careful haematological monitoring of FIV-positive cats with already existing anaemia. Blood transfusions may be indicated to gain time until the bone marrow recovers.

The formation of Heinz bodies which results in an accelerated Hb auto-oxidation and a decreased erythrocyte life-span is usually caused by oxidating drugs, diabetes mellitus, hyperthyroidism, lymphoma and chronic real failure, but is also seen in healthy cats (CHRISTOPHER, 1989; HICKMAN et al., 1990; WEISS et al., 1990; BAUER et al., 1991; CHRISTOPHER et al., 1989). This phenomenon may also be induced by Azidothymidine in some cats and contribute to the transient anaemia and bone marrow suppression.

Apart f rom possible adverse effects (anaemia, Heinz bodies), the permanent administration of Azidothymidine led t o a total recovery with good general condition without recurrence of any clinical signs for up t o 2 years. Long-term Azidothymidine therapy can induce resistance of the FIV, as it is reported from HIV infected humans, so that the risk of relapse and death is likely (RICHMAN et al., 1987; LARDER and KEMP, 1989; LARDER et al., 1989; R E M I N G T ~ N et al., 1991). However, the use of Azidothymidine seems to be beneficial in FIV-seropositive cats with clinical symptoms because of the patients' improved quality of life compaired with cats treated symp- tomatically.

References BAUER M. C., D. J . WEISS and V. PERMAN, 1991: Haematologic alterations in adult cats fed 6

or 12 % propylene glycol. Am. J . Vet. Res. 53, 69-72 CHRISTOPHER M. M., 1989: Relation of endogenous Heinz bodies to disease and anemia in cats:

120 cases (1978-1987). J. Am. Vet. med. Assoc. 194, 1089-1095 CHRISTOPHER M. M., V. PERMAN and J . W. EATON, 1989: Contribution of propylene glycol-

induced Heinz body formation to anemia in cats. J . Am. Vet. Med. Assoc. 194, 1045-1056 EGBERINK H., M. BORST, H. NIPHUIS, J . BALZARINI, H. NEU, H. SCHELLEKENS, E. DE

CLERQ, M. HORZINEK and M. KOOLEN, 1990: Suppression of feline immunodeficiency virus infection in vivo by 9-(2-phosphonomethoxyethyl)adenine. Proc. Natl. Acad. Sci. USA 87, 3087-3091

EGBERINK H. F., K. HARTMANN and M. C. HORZINEK, 1991: Chemotherapie bei Infektion mit dem felinen Immundefizienzvirus. XVI. pp. 227-229 WSAVA Congress, Vienna,

HALLMANN L., 1980: Klinische Chemie und Mikroskopie. 11th ed., Stuttgart, Thieme HART S. and I. NOLTE, 1990: Zur Thrombozytenaggregation der Katze. Tierarztl. Prax. 19,

413-418 HARTMANN K., A. DONATH, B. BEER, H. F. EGBERINK, M. C. HORZINEK, G. HOFFMANN-

FEZER, I. THUM and S. THEFELD, 1992: Use of two virustatica (AZT, PMEA) in the treatment of FIV and of FeLV seropositive cats. Vet. Immunol. Immunpathol. 35, 167-176

HASCHEK W. M., R. M. WEIGEL, G. SCHERBA, M. C. DEVERA, R. FEIN-MEHL, P. SOLT~R, M. B. TOMPKINS and W. A. TOMPKINS, 1990: Zidovudine toxicity to cats infected with feline leukemia virus. Fundam. Appl. Toxicol. 14, 764-775

HICKMAN M. A., Q. R. ROGERS and J . G. MORRIS, 1990: Effect of diet on Heinz body formation in kittens. Am. J. Vet. Res. 51, 475-478

KAMALI F. and M. D. RAWLINS, 1990: Simple and rapid assay for zidovudine and zidovudine glucuronide in plasma using high-performance liquid chromatography. J . Chromatogr. 530, 474-479

LARDER B. A. and S. D. KEMP, 1989: Multiple mutations in HIV-1 reverse transcriptase confer high-level resistance to Zidovudine (AZT). Science 246, 1155-1 158

LARDER B. A,, G. DARBY and D. D. RICHMAN, 1989: HIV with reduced sensitivity to Zidovudine (AZT) isolated during prolonged therapy. Science 243, 1731-1734

NORTH T. W., G. T. NORTH and N. C. PEDERSEN, 1989: Feline immuno-deficiency virus, a model for reverse transcriptase-targeted chemotherapy for acquired immunodeficiency syndrome. Anti-microb. Agents Chemother. 33, 915-919

REMINGTON K. M., B. CHESEBRO, K. WEHRLY, N. C. PEDERSEN and T. W. NORTH, 1991: Mutants of feline immunodeficiency virus resistant to 3'-azido-3'-deoxythymidine. J . Virol. 65, 308-312

Treatment of FIV-Seropositive Field Cats 409

RICHMAN D. D., M. A. FISCHL, M. H . GRIECO, M. S. GOTTLIEB, P. A. VOLBERDING, 0. L. LASKIN, J . M. LEEDOM, J. E. GROOPMAN, D. MILDVAN, M. S. HIRSCH, G. G. JACKSON, D. T. DURACK, S. NUSINOFF-LEHRMAN and the AZT COLLABORATIVE WORKING GROUP, 1987: The toxicity of Azidothymidine (AZT) in the treatment of patients with AIDS and AIDS-related complex. N . Engl. J . Med. 317, 192-197

S H O ~ S. , 1991: Nonparametric statistics. J . Am. Vet. Med. Assoc. 198, 1126-1128 WEISS D. J. , C. B. MCCLAY, M. M. CHRISTOPHER, M. MURPHY and V. PERMAN, 1990: Effects

of propylene glycol-containing diets on acetaminophen-induced methemoglobinemia in cats. J. Am. Vet. Med. Assoc. 196, 1816-1819

ZEIDNERN. S., M. H. MYLES, C. K. MATHIASON-DUBARD, M. J . DREITZ, J . I. MULL INS^^^ E. A. HOOVER, 1990: Alpha Interferon (Zb) in combination with Zidovudine for the treatment of presymptomatic feline leukemia virus-induced immunodeficiency syndrome. Antimicrob. Agents Chemother. 34, 1749-1 756