Polymeric drug based on sulfanilamide: Synthesis, antimicrobial and drug releasing studies

Article abstract of DOI:10.1211/jpp.59.9.0004

N-((4-amino sulfonyl)phenyl)acrylamide (APA) was synthesized using sulfanilamide and acryloyl chloride in the presence of triethyl amine at 0-5°C. Homo- and co-polymerization of 2-hydroxyethyl acrylate (HEA) and acrylic acid (AA) were done by adopting a solution polymerization technique using methyl ethyl ketone (MEK) as a solvent and benzoyl peroxide (BPO) as a free radical initiator at 70 ± 1°C. All the monomers and polymers were characterized by IR and NMR techniques. These monomers and polymers were tested for their antimicrobial activity against five different ATCC strain microorganisms (Escherichia coli (25922), Pseudomonas aeruginosa (27853), Klebsiella (70063), Salmonella typhi (6539) and Staphylococcus aureus (25923)). The effect of co-monomer, other than the active drug moiety present in the polymeric drug, is discussed. The antimicrobial activity of APA on Gram-positive bacteria was enhanced when copolymerized with AA and HEA. The polymer was made into a film form and that film was used for drug releasing study. The drug releasing rate was monitored by the absorption at 268 nm using a UV spectrophotometer. The effect of pH and the temperature on the drug releasing rate was monitored and found that the releasing rate was dependent on the co-monomer, pH and temperature of the medium.

Full text of DOI:10.1211/jpp.59.9.0004

JPP 2007, 59: 1207–1213
2007 The Authors
©
Received February 23, 2007
Accepted June 4, 2007
DOI 10.1211/jpp.59.9.0004
ISSN 0022-3573
Polymeric drug based on sulfanilamide: synthesis,
antimicrobial and drug releasing studies
C. Umamaheswara Reddy, A. Arun, A. Amalraj and B.S.R. Reddy
Abstract
N-((4-amino sulfonyl)phenyl)acrylamide (APA) was synthesized using sulfanilamide and acryloyl
chloride in the presence of triethyl amine at 0–5°C. Homo- and co-polymerization of 2-hydroxyethyl
acrylate (HEA) and acrylic acid (AA) were done by adopting a solution polymerization technique
using methyl ethyl ketone (MEK) as a solvent and benzoyl peroxide (BPO) as a free radical initiator
at 70 ± 1°C. All the monomers and polymers were characterized by IR and NMR techniques. These
monomers and polymers were tested for their antimicrobial activity against five different ATCC
strain microorganisms (Escherichia coli (25922), Pseudomonas aeruginosa (27853), Klebsiella (70063),
Salmonella typhi (6539) and Staphylococcus aureus (25923)). The effect of co-monomer, other than
the active drug moiety present in the polymeric drug, is discussed. The antimicrobial activity of APA
on Gram-positive bacteria was enhanced when copolymerized with AA and HEA. The polymer was
made into a film form and that film was used for drug releasing study. The drug releasing rate was
monitored by the absorption at 268 nm using a UV spectrophotometer. The effect of pH and the
temperature on the drug releasing rate was monitored and found that the releasing rate was
dependent on the co-monomer, pH and temperature of the medium.
Introduction
The design and application of polymeric drugs for human health is an interesting field that
is in continuous expansion and development because of intrinsic advantages offered by spe-
cific macromolecular systems in new and low-risk therapies. The use of polymeric systems
with pharmacological activity provides very good local activity, reducing the toxicological
risks, and in addition could act as a release system of the pharmacological active residue,
controlled by chemical reactions, mainly hydrolytic, under enzymatic and non-enzymatic
processes. These chemically modified drug conjugates are usually prepared by esterifica-
tion, acrylation or alkylation. By attaching bioactive substrates to the synthetic or naturally
occurring macromolecules, it is expected to increase therapeutic efficiency while lowering
toxicity. The basic idea behind this type of approach is that the substrate molecules would
undergo hydrolysis or enzyme-catalysed cleavage when introduced into the system (Harris
Sri Ramachandra College of
Pharmacy, SRMC&RI(DU),
Chennai-600 116, India
C. Umamaheswara Reddy,
A. Amalraj
Central Leather Research
Institute, Adyar, Chennai-600
1
984). Drugs that contain reactive functional groups, such as hydroxyl or carboxyl groups,
0
20, India
or amino groups, can be covalently linked to a wide variety of polymerizable derivatives
A. Arun*, B. S. R. Reddy
(
Ibrahim Erol 2004).
The activity of an antimicrobial drug initially starts from attacking the cell wall of a
microorganism. The effect of the drug on the lipid bi-layers has been described by Mouritsen
& Jorgensen (1994). According to Bolard et al (1991), the activity of antibiotic drugs is
mainly due to the ability of the drug to bind to the membranes, which in turn is controlled
by the lipid composition. The activity of the drug was enhanced and reported by several
research workers under the heading of amphiphilic drugs (Attwood et al 1974). A classical
review by Seeman (1972) described various reports on the membrane actions of the phar-
macologically active compounds. Several studies have further reported a controlled-release
system with hydrophilic character for curing chronic diseases by co-polymerising a drug
moiety with hydrophilic components (Davaran & Entezami 1997, 1998).
Correspondence: B. S. R. Reddy,
Central Leather Research
Institute, Adyar, Chennai-600
0
20, India. E-mail:
induchem2000@yahoo.com
*Present address: Govt. Arts
College, Tiruvannamalai,
Tamilnadu, India.
Acknowledgement: The
authors thank A. Anandkumar
for helping to improve the
quality of the manuscript.
Generally, the activity of the polymeric drug is related to the functional group and the
nature of the polymeric substance. According to Vogl & Tirrell (1979), the introduction of a
hydrophilic, hydrophobic or polyelectrolytic moiety will enhance the activity of the drug on
1207

1
208
C. Umamaheswara Reddy etal
microorganisms. Also, it was observed that poly(methacrylic Bruker CXP 320 MHZ in d -DMSO with TMS as an internal
6
acid) has no effect on microorganisms like E. coli. Incorporat- standard. UV-visible absorption measurement was conducted
ing hydroxyl or carboxylic groups in the polymer backbone on a Schimadzu model 160A spectrophotometer. Molecular
could in fact increase the hydrophilic character of the poly- weights of the polymers were obtained using Shimadzu
meric drug. Most of the synthesized polymeric drugs having instrument (India) using an IR detector and THF as an eluent
−
1
high hydrophilic character were produced by co-polymerizing at a flow rate of 0.3 mL min . Elemental analysis was done
the drug conjugates with acrylic acid as a hydrophilic part on a Coleman C-H-N analyser.
(Roman & Madruga 1989; Roman & Levenfeld 1990; Arshady
1
993; Boundreaux etal 1996; Thamizharasi etal 2002; Arun
Synthesis of N-((4-amino sulfonyl)phenyl)
acrylamide (APA)
etal 2003). Most of the acrylic type of synthesized drug mono-
mers and their polymers are pharmaceutically active com-
pounds (Arshady 1993). Significant pharmacological activity Sulfanilamide (8.61 g, 0.05 mol) and 200 mL of MEK were
is, however, seen if high-molecular-weight acrylic polymers taken in a 500-mL three-necked round-bottom flask fitted
are incorporated with active drugs (Liso etal 1995). The with a stirrer and thermometer. To this solution, 7.25 mL
advantage of acrylic acid as a co-monomer in a polymer chain (0.05 mol) of triethylamine was added. The resulting solution
bearing an active drug moiety is its ability to assist the cleavage was kept cool in an ice-bath for half an hour. Acryloyl chlo-
of amide or ester linkage through neighbouring group parti- ride (4.22 mL, 0.05 mol) was dissolved in 25 mL of MEK and
cipation mechanism (Savage etal 1978; Foolandi 1979). These taken into a pressure equalizer. To this cooled solution, acry-
properties make such systems quite interesting and provide loyl chloride was added drop by drop at 0–5°C for about half
longer delivery times with lower dosages.
an hour. After completion of the addition, the reaction mix-
Nowadays, resistance to sulfa drugs is common in all parts ture was kept at room temperature with constant stirring for
of the world (Skold 2000, 2001). The antimicrobial activity of 3 h. The mixture was then filtered and the quaternary ammo-
sulfanilamide is due to its structural analogy with p-aminoben- nium salt was removed. The organic filtrate was washed three
zoic acid (PABA), which is involved in dihydrofolic acid syn- times with 50 mL distilled water to remove the unreacted
thesis. Sulfanilamide can competitively inhibit dihydropteroate reactants. The aqueous layer was removed and the organic
synthesis by its structural analogy with PABA substrate. It can layer was dried in a beaker containing anhydrous sodium sul-
also function as an alternative substrate for dihydropteroate syn- fate for about 10 min. The resultant liquid was evaporated to
thase (DHPS), forming a pterin adduct that cannot participate in get a crude acrylated product. The crude product was recrys-
the folate synthesis and ultimately diffuses from the cell. The tallized using methanol. Yield = 10.26 g. Melting point = 135–
−
1
idea behind our research work is to improve the antibacterial 137 °C. IR (cm ): 3476 (NH), 3050 (aromatic CH), 1674
activity of sulfanilamide (without altering the basic structure (amide C = O), 1629 (CH = CH), 1595 (aromatic CH = CH),
1
and mode of action) by incorporating the hydrophilic co- 1195 (S( = O) ), 834 (1,4-substitution of benzene). H NMR
2
monomer in the polymer chain, which already bears the phar- (d, ppm): 10.5 (s, NH), 7.9–8.2 (m, Aromatic protons), 6.5 (t,
1
3
macologically active agent (sulfanilamide). Also, the co-mono- vinylic CH), 6.0 (s, NH ) and 5.8 (d, vinylic CH ). C NMR
2
2
mer can be involved in the hydrolysis of the sulfanilamide from ((d, ppm): 118 (vinylic CH ), 126 (vinylic CH), 128, 131,
2
the polymer chain and thereby produces a sustained drug deliv- 138, 141 (aromatic) and 163 (ester C = O). Elem. Anal. Calcd.
ery system. The drug-releasing behaviour of the polymer sam- for C H N O S: C, 47.78%; H, 4.45%; N, 12.38%. Found:
9
10 2 3
ple was measured using UV visible spectroscopic technique.
C, 47.82%; H, 4.42%; N, 12.35%.
Synthesis of poly(APA)
Materials and Methods
A free radical solution polymerization technique was used for
preparing the homopolymers. APA (1.13 g, 0.005 mol),
Materials
10 mL of MEK and 0.023 g (2 wt%) of BPO were taken in a
2-Hydroxyethyl acrylate (HEA), triethylamine and acrylic polymerization tube. The mixture was flushed with a slow
acid (AA) were obtained from Fluka and used as such. Ben- stream of oxygen-free nitrogen for about 15 min. The tube
zoyl peroxide (BPO) (Fluka) was purified by recrystallization was tightly sealed and immersed in a thermostatic water bath
using methanol–chloroform (1:1). Methyl ethyl ketone for 24 h at 70 ± 1°C. The homopolymer was precipitated using
(
MEK), methanol, dimethyl sulfoxide (DMSO) and acryloyl excess methanol. The precipitate was filtered off and dried in
−
1
chloride were received from Aldrich Chemicals and purified vacuum at 30°C for 12 h. Yield= 1.02 g. IR (cm ): 3328
according to standard procedure. Muller-Hinton broth and (NH), 3082 (aromatic CH), 2939 and 2912 (aliphatic CH),
Muller-Hinton agar were obtained from Himedia and used as 1594 (aromatic CH = CH), 1332 and 1181 (S0 ), 833 (1, 4-
2
1
such. ATCC strains of Gram-negative bacteria (Escherichia substitution of benzene). H NMR (d, ppm) 5.9 (NH-SO ),
coli (25922), Pseudomonas aeruginosa (27853), Klebsiella 7.9–8.2 (m, Ar-H), 10.5 (Ar-NH), 1.2–1.5 (m, CH and CH of
2
2
(
(
70063), Salmonella typhi (6539)) and Gram-positive bacteria polymeric backbone).
Staphylococcus aureus (25923)) were obtained from the
Christian Medical College (CMC; Vellore, India) and used
for culturing the bacteria. FT-IR spectra of copolymer sam-
Synthesis of poly(APA-co-AA)
ples were recorded on Nicolet 20DXB (USA) using KBr pel- APA (0.905 g, 0.004 mol) and 0.29 g (0.004 mol) of AA,
1
13
lets. H and C NMR spectra of the samples were run on 10 mL of MEK and 0.024 g (2 wt%) of BPO were used for the

Polymeric drug based on sulfanilamide
1209
−
1
synthesis of poly(APA-co-AA). Yield= 0.88 g. IR (cm ): Preparation of film
231 (NH and OH), 2921 (aliphatic CH stretch), 1684 (amide
C = O), 1643 (acid C = O), 1410 (OH bending of acid), 1320
SO ), 940 and 980 (acid stretching), 840 (1,4 substituted
3
The drug sample (200 mg) was dissolved in a minimum quan-
tity of the DMSO. The resulting solution was placed into a
film forming glass plates. This glass plate was dried in vac-
uum at 30°C for 24 h. The film was peeled from the glass
plate and the thickness of the film was measured using an
electronic screw gauge. The thickness of the film was 100–
(
2
1
benzene) and 700 (aromatic CH, out of plane bending). H
NMR (d, ppm): 5.9 (s, NH-SO ), 7.9–8.2 (m, Ar-H), 10.5 (s,
Ar-NH), 11.5 (s, OH) 1.2–1.5 (m, CH and CH of polymeric
2
2
backbone).
200 mm. This film was used for the controlled drug delivery
studies.
Synthesis of poly(APA-co-HEA)
APA (0.905 g, 0.004 mol) and 0.464 g (0.004 mol) of HEA, In-vitro drug release study
1
5 mL of MEK and 0.027 g (2 wt%) of BPO were used for the
The in-vitro drugs release pattern was studied at different
−
1
synthesis of poly(APA-co-HEA). Yield = 0.94 g. IR (cm ):
temperature (37 and 40°C) and at different medium pH (7.4
3
1
349 (NH and OH), 1732 (amide C = O), 1693 (ester C = O),
2
and 9.2). Pieces (1–1.5 cm ) of co-polymer films (100–
598 (Ar-C = C), 1361 (SO ), 1148 (C-O stretching) and 796
2
200 mm thickness) were taken and soaked in 10 mL of phos-
1
(
substituted aromatic CH, out of plane bending). H NMR (d,
phate-buffered solutions of pH 7.4 and 9.2. Five millilitres of
the solution were periodically collected for analysis and
replaced by the same volume of fresh medium. The amount
of APA in the medium was determined using UV spectros-
ppm): 5.9 (s, NH-SO ), 7.2–8.2 (m, Ar-H), 4.3 (s, OH), 3.3–
2
3.6 (m, O-CH ) and 1–1.5 (m, CH and CH of polymer back-
2
2
bone).
copy absorption at l = 268 nm. These measurements were
max
Drug susceptibility test
performed by a UV/visible detector systronic system. The
cumulative drug released was plotted against the time inter-
vals. All the experiments were done in triplicate.
The drugs were tested by a disc-diffusion method. Diluted
bacterial cultures (100 mL) were spread on sterile Mueller-
Hinton agar plates, after which 8-mm-diameter discs (sterile
blank) impregnated with drug to be tested (100 mg) were
placed on the plates. The plates were incubated for 24 h at
Results and Discussion
3
7°C under aerobic conditions and the diameter of the inhi-
bition zone around each disc was then measured and A novel APA monomer carrying an active drug moiety was
recorded. If the drugs were found to be active in the disc- synthesized, at high purity, using sulfanilamide and acryloyl
diffusion test (inhibition zone > 10 mm), they were further chloride (Figure 1). Co-polymerization was done using AA
evaluated for determining minimum inhibitory concentra- and HEA with a view to increasing the interaction between
tion (MIC) values.
the polymer chain to that of the cell wall of microorganism
Figure 2). All the monomers and polymers were character-
ized by IR and NMR techniques. The average molecular
(
Minimum inhibitory concentration (MIC)
−
1
weight of polymers was around 6000 g mol (Table 1). The
The drugs were screened for their antibacterial activity polydispersity values of the polymers were < 2, quantitatively
against E. coli, P. aeruginosa, Kelbsiella, S. typhi and S. suggesting that the polymer was terminated by disproportion
aureus. MIC was evaluated by turbidity method. A loopful method, which was typical of acrylates.
of bacteria was inoculated in 100 mL of nutrient broth at
−
1
3
7°C for 20 h in a test-tube shaker at 150 rev min . The test
compounds were prepared by dissolving in a minimal vol-
ume of DMSO and were serially diluted in Mueller-Hinton The MIC values (average of triplicates) of the sulfanilamide,
Antimicrobial activity
−
1
broth at concentrations in the range of 1–100 mg mL . The APA monomer, poly(APA), poly(APA-co-AA) and
4-h bacterial cultures were then transferred into 10 mL of poly(APA-co-HEA) are shown in Table 1. The effect of the
2
Muller-Hinton broth (control and test compounds) and incu- co-monomer in the polymer chain on the antimicrobial activ-
bated at 37°C for 24 h. The growth of the bacteria was ity was investigated by comparing the MIC values of
determined by measuring the turbidity after 24 h. Thus, the poly(APA), poly(APA-co-AA) and poly(APA-co-HEA). The
MIC was generally read as the smallest concentration of results showed that the presence of hydrophilic co-monomer
drug in the series that prevents the development of visible in the polymer chain enhanced the antimicrobial activity on
growth of test organism. All the experiments were done in the Gram-positive bacteria. The activity of poly(APA-co-AA)
triplicate.
against S. aureus was found to be very high. The MIC value
−
1
(
3 mg mL ) was higher than, or equal to, the MIC value of
linezolid (Ford et al 1999) (a new oxazolidinone class of com-
pound), which is in early phase III of human clinical trials.
Statistical analysis
The MIC value and the drug releasing rate were measured in Besides having a similar MIC value, the synthesis of
triplicate. Statistical analysis of the MIC value was performed poly(APA-co-AA) was very simple, making it a good com-
using the unpaired Student’s t-test. Differences were consid- petitor for the oxazolidinone class of compound. But, in the
ered significant when P <0.01.
case of Gram-negative bacteria, the antimicrobial activity was

1
210
C. Umamaheswara Reddy etal
CH CH2
CH CH2
NH2
n
C
O
O
CH CH2
C
BPO
EMK
+
NH
70 ± 1°C
NH
C
O
0–5°C
C1
SO NH2
2
SO NH
SO NH
2 2
2
2
Figure 1 Synthesis of APA and poly(APA).
CH CH2 CH CH2
CH CH2
n
CH CH2
C
O
C
O
R
O
C
O
BPO
0 ± 1°C
C
O
R
O
NH
n
NH
n
+
7
SO NH
2
SO NH2
2
2
Where,
R = H or CH CH OH
2
2
Figure 2 Monomeric units present in the co-polymer chain.
Table 1 Molecular weight and MIC (mg mL−1) value of APA, poly(APA), poly(APA-co-AA) and poly(APA-co-HEA)
MW ´ 103
M ´ 10
3
MW/Mn
Compound
E. coli
S. aureus
P. aeruginosa
Klebsiella
S. typhi
n
Sulfanilamide
APA
Poly (APA)
Poly(APA-co-AA)
Poly (APA-co-HEA)
12.7 ± 0.27
13.4 ± 0.16
12.9 ± 0.22
13.0 ± 0.25
11.9 ± 0.56
24.1 ± 1.33
13.1 ± 0.34
12.2 ± 0.48
3.1 ± 0.17
6.3 ± 0.59
12.5 ± 0.86
6.3 ± 0.42
6.3 ± 0.66
6.7 ± 0.52
6.9 ± 0.18
12.9 ± 0.40
11.7 ± 0.66
6.7 ± 0.14
13.1 ± 0.98
11.5 ± 0.27
25.4 ± 1.08
12.0 ± 0.44
5.7 ± 0.37
6.0 ± 0.50
12.8 ± 0.14
—
—
4.86
6.39
6.08
—
—
3.04
3.51
3.67
—
—
1.60
1.82
1.66
MIC was calculated using three values.
found to be unaltered or decreased (Table 1) when the active hydrophilic nature of the poly(APA-co-AA) chain bearing the
drug moiety was co-polymerized with AA or HEA. Differ- active drug moiety provided a considerable advantage for
ences in the cell wall constituents of microbes might have effective penetration through the outer membrane of P. aeru-
brought about such a variation in the co-monomer effects ginosa, thereby efficiently inhibiting the folic acid synthesis.
between the two types of strains (Prescott et al 2002). In the
The antimicrobial property of co-monomer AA in
case of Gram-negative bacteria, the remarkable observation poly(APA-co-AA) is not apparent and can be ruled out as
lies in the MIC value of P. aeruginosa. P. aeruginosa is con- poly(AA) showed absence of any antimicrobial activity in simi-
sidered to be a highly resistant species among the Gram-nega- lar systems (Vogl & Tirrell 1979). This provides a clear picture
tive bacteria (Normark & Normark 2002). Several studies that the enhancement of antimicrobial activity against S. aureus
have demonstrated the low susceptibility of P. aeruginosa of poly(APA-co-AA) over that of poly(APA) was due to the
towards both hydrophobic and hydrophilic antibiotics availability of active drug moiety (sulfanilamide) adjacent to the
(
Nikaido 2000, 2001). The MIC value of poly(APA-co-AA) cell wall of the microorganism or the opening up of the cell wall
−
1
over P. aeruginosa, although found to be high (6.7 mg mL ) to allow the active drug moiety to penetrate through and inter-
considering the intrinsic resistance of the bacterium, repre- fere with the folic acid synthesis. With regards to the first condi-
sented
a considerable advantage. Besides, the high tion, we feel that the availability of the drug adjacent to the cell

Polymeric drug based on sulfanilamide
1211
wall was increased due to the polymeric chain forming a cage-
like structure around the microorganism.
50
40
30
20
10
0
Such structures could be stabilized by both ionic and hydro-
gen bonding between the polymeric chain and the cell wall of the
microorganism (Bolard etal 1991). As for as the second possibil-
ity, cell wall opening can be triggered by the ionic strength and
the hydrophilic nature of the medium adjacent to the cell wall of
the microorganism (Arshady 1993; Roman & Madruga 1989).
In poly(APA-co-AA), the co-monomer AA was involved in
increasing the ionic strength of the medium adjacent to the cell
wall of the microorganism. It appears from the results that these
two factors operate simultaneously to increase the activity of
poly(APA-co-AA) over that of poly(APA) and poly(APA-
co-HEA). The co-monomer AA acts as an anchor to deliver the
active drug moiety through the above-said two mechanisms.
0
100
200
300
400
500
600
700
Effect of co-monomer on S. aureus
Time (h)
When we compared the activity of the poly(APA-co-AA)
with that of poly(APA-co-HEA) on Gram-positive bacteria,
the former was twice as active. This might be attributed to the
greater ionic strength of AA than HEA, which enhances the
antimicrobial activity considerably. Moreover, the AA present
Figure 4 Effect of pH and temperature (diamonds = pH 9.2 at 37°C,
squares = pH 7.4 at 40°C and triangles = pH 7.4 at 37°C) on the drug
releasing rate of copoly(APA-HEA) film (average ± s.d., n = 3).
in the poly(APA-co-AA) can engage in neighbouring group that in slightly alkaline pH (pH 7.4), the amide linkage that con-
participation mechanism for the detachment of active drug nects the drug to the polymer backbone is resistant to hydrolysis.
moiety from that of the polymeric chain (McCormick 1985). The drug releasing graph clearly indicates that the releasing pat-
This also will add to the evidence that poly(APA-co-AA) is a tern was not uniform in nature. This may be due to the irregular-
very active polymeric drug when compared with poly(APA) ity in the drug releasing pattern shown by the polymeric film.
and poly(APA-co-HEA) towards Gram-positive bacteria.
Earlier studies have reported a similar type of irregularity in the
release of the drug and this can be overcome by changing the
type of testing sample from the film type to granular type
Controlled release studies of copolymers
(Sharkawi etal 2005). Since we were studying a releasing pattern
The drug release pattern for polymer carrying AA and HEA as a at different temperatures, we intended to go for the film type
co-monomer is shown in Figures 3 and 4. This showed that the rather than granular type of testing sample. The drug releasing
rate of release of active drug moiety from the polymer backbone pattern in the acidic medium was not studied here since the
was enhanced when the pH of the medium was changed from amide linkage showed more stability towards hydrolysis (Gal-
7
.4 to 9.2 (Arun & Reddy 2005). This might be due to the fact lardo etal 2001) in acidic conditions. As the basicity of the
medium increased, the amide linkage was more prone to hydrol-
ysis and released the active drug moiety to the surroundings
(
Elvira etal 2001) at a faster rate. The other factor that was
1
00
responsible for the higher release rate of the drug was the pres-
ence of the aromatic system of the drug over an aliphatic system.
This sort of aromatic system, exhibiting a faster release rate than
an aliphatic system, has been observed by many previous
research workers (Gallardo etal 2001). The hydrolysis of the
amide bond in the basic medium was reported earlier (Mikes etal
7
5
2
5
0
5
0
1
974; Gallardo & Sanroman 1993; Elvira etal 2001). We
observed a slight increase in the release rate of the drug when the
temperature was changed from 37°C to 40°C at pH 7.4. This is
due to the fact that the temperature increases the chain mobility,
which in turn allows the water molecules to penetrate through
the polymer matrix to enhance the hydrolysis rate of the system.
This sort of chain mobility, responsible for the enhancement of
releasing rate and the effect, may be more pronounced when the
polymer sample was in film form. This type of pH responsive-
ness has major advantages — one of the most important being
sustained oral drug delivery provided by the pH difference
between the stomach and the intestine (Davaran etal 1999).
From the comparative graph (Figure 5), it is evident that
the polymer sample made up of AA released the drug at a
0
100
200
300
400
500
600
700
Time (h)
Figure 3 Effect of pH and temperature (diamonds = pH 9.2 at 37°C,
squares = pH 7.4 at 40°C and triangles = pH 7.4 at 37°C) on the drug
releasing rate of copoly(APA-AA) film (average ± s.d., n = 3).

1
212
C. Umamaheswara Reddy etal
wall of the microorganism. Even though several other authors
previously reported these two types of mechanisms, this is the
first time that we have reported this methodology to increase
the antimicrobial activity of sulfanilamide. The drug releasing
pattern of the polymer film was monitored for 4 weeks using
UV/visible spectroscopic technique. The drug releasing graph
suggests that the co-monomer, pH and the temperature of the
medium affect the releasing rate of drug from the polymer
film. We also found that the rate of release increased upon
increasing the pH and temperature of the medium. Also, an
enormous difference in releasing behaviour was observed
between poly(APA-co-AA) and poly(APA-co-HEA).
1
00
7
5
2
5
0
5
0
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Figure 5 Effect of co-monomer type (diamonds =AA, squares = HEA) Arun, A., Reddy, B. S. R. (2005) In vitro drug release studies from
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