THE RELEASE OF ANTIBIOTICS FROM BONE CEMENT

William Quinlan and Cormac Mehigan

Department of Surgery, University College, Dublin.

Summary

RELEASE of antibiotic from bone cem- ent has been shown using in vitro

studies. This report records the results of a comparative in vivo study performed in rabbits in which 4 bone cements and 2 antibiotics--sodium fusidate and gen- tamicinmwere compared. Sodium fusid- ate was released in quantities varying from 0.014 to 0.530 /~g/ml. Periods of release ranged from 45 to 187 days. For gentamicin the periods of release varied from 31 to 101 days and the antibiotic levels recorded lay between 0.008 and 0.4/~g/mi.

Introduction

For a number of years, the use of poly- methylmethacrylate bone cement as an anchoring agent in total joint replace- ment has been an accepted procedure. This cement is produced commercially as Palacos, C M W, Simplex and Sulfix. Each differs slightly. The standard uni~ consists of 40g of powder polymer and 20ml of liquid monomer. The process of polymerisation takes place after mixing the powder and liquid, the heat of poly- merisation being 13.28 K.Cal/mol. Tem- peratures up to 90~ have been recorded during polymerisation.

Addition of antibiotics to bone cement has been the most recent orthopaedic advance in an effort to combat infection following joint replacement. Rauch- Puntigram and VSIker (1967) showed that the polymerised bone cement released monomer. With this knowledge Buch- holz and Engelbrecht (1970) carried out in vitro studies on antibiotic release from Palacos. They established for the first time that gentamicin, erythromycin,

cephalosporins and penicillin were re- leased from Palacos. StShr et al (1973) observed good bone levels of gentamicin following implantation of Palacos-genta- micin. Further importance was attributed to these findings when Voorhoeve and StShr (1973) showed good clinical re- sults from treatment of osteomyelitis with Palacos-gentamicin implants. Wahlig et al (1972) showed by studies on humans and experimental animals that serum levels were minimal and short-lived and urine levels were very low and persisted for about 10 days, following implantation of the Palacos-gentamicin in bone.

One of the most promising in vivo studies of antibiotics (gentamicin, ceph- alosporin and oxacillin) in bone cements (Simplex and Palacos) was set up by marks et al (1974, 1976). Unfortunately it was concluded after 21 days. Elson e.t al (1977a) showed that antibiotics incor- porated into bone cement were effective in reducing haematogenous infection of the implants. In a well controlled study Elson et al (1977 b) found that by incor- porating either sodium fusidate or genta- micin into Simplex or Palacos, the de- gree of infection in rats tibiae could be reduced by varying amc)unts. These lat- ter findings were most relevant when applied to joint replacement.

From a very thorough review of the literature, it appears that for implantation in bone cement, gentamicin has received more attention than any other antibiotic. The bone cement most frequently stud- ied has been Palacos. The great major- ity of reports concerned in vitro studies.

It therefore seemed that an in vivo self-terminating comparative study, using all 4 bone cements and more than one antibiotic, should be set up.

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426 IRISH JOURNAL OF MEDICAL SCIENCE

Materials and Methods A series of experiments was commen-

ced. In these the 4 bone cements and sodium fusidate and gentamicin were used. This gave 8 combinations. Ten rabbits were chosen for each combina- tion.

Each rabbit was anaesthetized by in- travenous injection of 60rag of pentcbar- bital sodium. Anaesthesia was continued with open mask ether. Using fully aseptic operative procedures, the right thigh of each rabbit was opened via an oblique incision. The femoral shaft was entered through the greater trochanter and the medullary canal was was reamed to 4.5 mm in diameter. A second skin incision was placed over the right knee and a drill hole was made through the lower femur. Saline washing was then used to clear the medullary contents from above to below.

Two grams of antibiotic powder (sod- ium fusidate or gentamicin) were mixed with 80 g of bone cement powder (Pala- cos, C M W, Simplex or Sulfix), 40 ml of liquid monomer was added and mixed and polymerisation .commenced. The right femoral canal of each rabbit was then filled with the appropriate antibiotic- bone cement combination. Filling was stopped as the cement got to within 2 cm of the proximal end. At this stage a wide bore metal cannula with sidewall perforations was inserted between bone and cement. Its upper end lay subcut- aneously. The surgical incisions were then closed in layers. Unrestricted activ- ity was allowed post-operatively. Saline lavages through the metal cannulae were done 1, 3, 5, 10, 17 and 31 days post- operatively and thereafter at 2 weekly intervals. Using 3 ml of saline in a syringe, the skin was punctured with a needle and the cannula was entered. Lavage was carried out for 30 s. The con- tents was then either assayed or stored at -20~ for later assay.

When no antibiotic was found in the lavage fluid on 3 consecutive lavage days, the antibiotic was considered to

have ceased diffusing from the cement mass.

After the right femur of the rabbits chosen for each combination had been filled, the residue of antibiotic-bone cem- ent was put in 2 metal cylinders 7.5 cm long and 1.5 cm wide. After hardening, the mass was driven from each cylinder and cut into discs 2 mm thick. These were put in saline and incubated at 37~ Each day the discs, after washing, were put in fresh saline. On the day of each lavage, a disc was taken from the saline and placed on an agar diffusion plate containing the appropriate test organ- ism. This was the in vitro part of the study.

The method of antibiotic assay used was that of Arret et al (1971). For assay of gentamicin the test organism was Staphylococcus epidermidis. A 30% sus- pension of the organism in N.I.H. broth was made and 0.1 ml of the suspension per 100 ml of assay medium was used. In- hibition of growth of the test organism was compared with that of a standard curve prepared from a known antibiotic concentration.

For sodium fusidate assay, Corynebac- terium xerosis was the test organism. The organism was grown in N.I.H. broth for 4 to 6 hours and its transmittance was read on a spectrophotometer at 650 m/~. Inhibition of the test organism was compared with that of a standard curve prepared from a known concentration of sodium fusidate.

Results Gentamicin was released from Sim-

plex cement for up to 87 days. The mini- mum period was 59 days and the mean duration of release was 80 days (Table I). The amounts of antibiotic released varied from 0.008 #g/ml to 0.40 Fg/ml of lavage fluid (Fig. !) .

When gentamicin was added to C M W it was released in lesser amounts and for a rather similar period. The minimum period was 59 days and the maximum was 101 days. The mean was 79 days

THE RELEASE OF ANTIBIOTICS FROM BONE CEMENT 427

TABLE I Duration of release of gentamicin from bone

cements (days)�9

Simplex C.M.W. Sulfix Palaces

59 59 31 11 87 101 59 87 87 59 45 31 59 101 59 87 87 59 59 73 87 59 45 31 87 87 45 45 73 73 31 45 87 101 45 31 87 87 31 45

(80) (79) (45) (50)

() denotes mean�9

(Table I). Antibiotic levels ranged from 0.008/~g/ml to 0.26/~g/ml (Fig. 1).

The duration of release was diminished when gentamicin was added to Sulfix. The minimum period was 31 days and the maximum was 59 days. The mean duration of release was 45 days (Table I). The recorded levels of antibiotic were from 0.008/~g/ml to 0.40/~g/ml of lavage fluid (Fig. 1).

Release of gentamicin from Palaces cement was rather similar to that with C M W and Simplex�9 The mean duration

Antiblotiom ,ug/ml

Gentamlc|n [r Simplex

i i . . . . Gentarnlcin Er C M W . . . . . . Gentarnicin ~ Sulfix 0.40 - ' , . . . . . . . . Gentamicin[t Palacos

0.35 �9 !

0 . 3 0

O. 2 5

0 20

0.15

0�9

~ k 0 . 3 ~ . . . . . . . ; . . . . . . . . . . . . . . . . ~ -",-~,

0 . 2 10 20 30 40 50 60 70 80 90

Days

Fig. 1--Pattern of release of gentamicin from bone cements�9

was 50 days. The maximum was 87 days and the minimum was 31 days (Table I). Antibiotic levels ranged from 0.008/zg/ml to 0.40 #g/ml of lavage fluid (Fig. 1).

Sodium fusidate was released from Simplex in levels up to 0.530 /~g/ml of lavage fluid. Lowest recorded levels were 0.05 /~g/ml (Fig. 2). The longest duration of release was 59 days. Mini- mum duration was 45 days and the mean release period was 56 days (Table II).

When sodium fusidate was released from C M W good levels were obtained, ranging from 0.530/~g/ml to 0.014/zg/ml of lavage fluid (Fig. 2). The mean dur- ation of release was 140 days with a maximum of 187 days and a minimum of 73 days (Table II).

{2_ } - o tn

F

0 . 5 5 - - - - - - S I M P L E X

0 . S0 ' i . . . . . . . . . . . . . C M W . . . . . . . S U L F I X

0 . 4 5 ~ PALACOS

~176 ! 0 . 3 5 -

0 . 3 0

0 . 2 5 i \ "

0 . 2 0 " ! - \

o ls \ \

0 . 1 o . ~-.-....:k:....N......... �9 ~ , ~ ~-....

oo5 , . . ~ ' . ~ ; . ; '.1~"~" 10 20 30 40 50 60 70 80 90 100 110 120 187

DAYS Fig�9 2--Pattern of release of sodium fusidate

from bone cements�9

The release of sodium fusidate from Sulfix was high at first�9 Levels reached 0.530 /zg/ml. Lowest levels were 0.07 /zg/ml of lavage fluid (Fig. 2). Antibiotic was detected for periods varying from 31 days to 73 days. The mean was 50 days (Table II).

The in vitro disc studies showed that sodium fusidate was released from Sim- plex for 115 days, from C M W for 187 days, from Sulfix for 87 days and from Palaces for 115 days.

Gentamicin was released in vitro from Simplex for 73 days, from C M W for 115 days, from Sulfix for 101 days and from Palaces for 87 days.

428 IRISH JOURNAL OF MEDICAL SCIENCE

TABLE II Duration of release of sodium fusidate from

bone cement (days).

Simplex C.M.W. Sulfix Palacos

59 187 59 115 59 187 45 87 59 143 31 59 45 87 73 115 59 73 31 59 59 115 73 59 59 129 45 59 45 157 45 59 59 187 59 59 59 143 45 59

(56) (140) (50) (73)

() denotes mean.

Discussion This study has shown that gentamicin

and sodium fusidate are released from all bone cements when implanted in vivo in rabbits' femora. Recorded levels are expressed in/~g/ml of lavage fluid. The total amount retrieved at each washing was the recorded level multiplied by 3 (3 ml of lavage fluid). This means that significant amounts of antibiotic are pre- ssnt at the cement-bone interface.

Rabbits form fibrous tissue very read- ily so it was possible that ingrowth of fibrous tissue into the metal cannulae might have resulted from repeated lav- ages. This would have prevented lavage fluid reaching the cement-bone interface. Autopsy revealed that all cannulae were still patent. Post mortem specimens of bone and cement were taken form each rabbit for antibiotic assay. No diffusion occu Fred.

There is no previous similar type of in vivo study with which we can compare our results. A comparative in vitro study by Holm and Vejlsgaard (1976) showed that C MW released gentamicin poorly for only 30 days. Our results for this com- bination differ significantly. Palacos, C M W and Simplex appear to be satis- factory carriers and releasers of genta- micin. Ger et al (1977) found that C M W

and Simplex still released gentamicin in vitro after 150 days of storage.

When sodium fusidate was added to bone cement Ger et al (1977) showed in vitro release from C M W and Simplex for 150 days. We have found that sodium fusidate was released from Palacos, Simplex or CM W at least 73 days in vivo.

Our in vitro results differed consider- ably from those in vivo, confirming the suggestion of Hill et al (1977) than an in vitro situation cannot be likened to an in vivo one.

The clinical application of this study would appear to be mainly in the treat- ment of high risk cases, e.g. joints which had previous surgery or injections, dia- betics and revision of previously infected ted joint replacements (Buchholz and Gartmann, 1972).

We wish to thank Mr. T. Buckley, A.I.M.L.T. who performed the antibiotic assays; Mr. N. O'Connor and staff in the Department of Surgery; Messrs. Leo Laboratories who supplied the sod- ium fusidate, and Messrs. Roussel Laboratories who supplied the gentamicin.

References Arret, B., Johnson, D. and Kirshbaum, A. 1971.

Outline of details of microbiological assays of antibiotics. J. Pharm. Sc. 60, 1689.

Buchholz, H. and Gartmann, H. 1970. Infektion- sprophylaxe und operative Behandlung der schleichenden tiefen Infektion bei der totalen Endoprosthese. Chirurg, 43, 446.

Buchholz, H. and Engelbrecht, H. 1972. Uber die Depotwirkung einiger Antibiotica bei Vermis- chung mit dem Kunstharz Palacos. Chirurg, 41, 511.

Elson, R. A.0 Jephcott, A. E., McGechie, D. B. and Verretas, D. 1977 a. Endogenous infection of acrylic cement, an animal study. J. Bone Jt. Surg. 59B, 500.

Elson, R. A., Jephcott, A. E., McGechie, D. B. and Verretas, D. 1977 b. Bacterial infection and acrylic cement in the rat. J. Bone Jt. Surg. 59B, 452.

Ger E., Dall, D., Miles, T. and Forder, A. 1977. B~)ne cement and antibiotics. S. Afr. Med. J. 51, 276.

Hill, J., Klenermann, L., Trustey, S. and Blowers, R. 1977. Diffusion of antibiotics from acrylic bone cement in vitro. J. Bone Jt. Surg. 59B, 200.

THE RELEASE OF ANTIBIOTICS FROM BONE CEMENT 429

Holm, N. J. and Vejlsgaard, R. 1976. The in vitro elution of gentamicin sulphate from methylmeth- acrylate bone cement. Acta. Orthop. Scand. 47, 144.

Marks, K. E., Nelson, C. L. and Schwartz, J. 1974. Antibiotic impregnated acrylic bone cem- ent. Surg. Forum, 25, 493.

Marks, K. E., Nelson, C. L. and Lautenschlager, E. P. 1976. Antibiotic impregnated acrylic bone cement. J. Bone Jt. Surg. 58A, 358.

Rauch-Puntigam, S. and Volker, H. 1967. Acryl und Methacryl verbim-dungen. Berlin-Heidel- berg o New York, Springer p. 37.

StShr, C., Finkbeiner, G. and Wahlig, H. 1973. Laingzeitbe obachtungen am Menschen uber die Friesetzung un Gentamycin aus Palacos R. Paper read at First International Congress on Prosthetics Techniques and Functional Rehab- ilitation, Vienna.

Voorhoeve, A. and St~hr, C. 1973. Ergenbisse bei der Behandlung der Chronische-eitrigen Osteomyelitis mit einem Palacos Gentamycin. Gemisch. Munch. Med. Wschr. 115, 20.

Wahlig, H., Hameister, W. and Grieben, A. 1972. Uber die firesetzung van Gentamycin aus Poly- methylmethacrylat. Langenbecks Arch. Chir. 331, 169.