Journal of Antimicrobial Chemotherapy (1975) 1, 323-331
Activity of minocycline and tetracycline against respiratory pathogens related to blood levels
Medical Unit* and Department of Medical Microbiology, The London Hospital, London E.I, England
A study was made of minocycline as a potential agent for use in respiratory tract infections. Pharmacological studies in 6 volunteers confirmed that serum levels of minocycline in the range 2-0 to 4-0 ug/ml can be obtained using a standard loading dose of 200 ng. In a cross-over study with tetracycline, minocycline showed more uniform absorption. At clinically achievable levels minocycline was more active than tetracycline against both tetracycline-sensitive and -resistant strains of Haemophilus species and Streptococcus pneumoniae. Minocycline at 2 ug/ml inhibited 96% of the 90 strains of both species. With P-haemolytic streptococci, however, the MICs of minocycline for tetracycline-resistant strains always remained above attainable blood levels. Introduction
Minocycline is an alkylated aminotetracycline which has been shown to be more effective than other tetracyclines against tetracycline-sensitive organisms but, additionally, it has activity against tetracycline-resistant and methicillin-resistant staphylococci (Steigbigel, Reed & Finland, 1968a; Minuth, Holmes & Musher, 1974), and tetracyclineresistant Proteus species (Simmons, 1974). Over recent years the emergence of tetracycline-resistant strains of respiratory pathogens, especially p-haemolytic streptococci (Robertson, 1965, 1968; Fallon, 1973), pneumococci (Percival, Armstrong & Turner, 1969) and Haemophilus influenzae (Williams & Andrews, 1974) has become increasingly apparent. The present study was designed to compare the activity of minocycline and tetracycline against the common respiratory pathogens. In addition we determined the blood levels attained after a single dose in order to assess the potential use of minocycline in the treatment of respiratory infections due to tetracycline-sensitive and tetracycline-resistant organisms. Methods
A total of 51 strains of Haemophilus species, 39 strains of pneumococci and 25 strains of group A streptococci were isolated from a variety of upper respiratory sites. Tetracycline-resistant strains were particularly selected for study. The sensitivity of the 323
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
M. J. Wood*, W. Farrell, S. Kaftan and J. D. Williams
324
M. J. Wood, W. Farrell, S. Kattan and J. D. Williams
Results
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
organisms to minocycline and tetracycline was determined by incorporating each antibiotic with DST agar (Oxoid) containing either 5 % horse blood (for group A streptococci and pneumococci) or 0 0 5 % lysed horse blood containing 10 ng/ml NAD (for Haemophilus), to give a range of final concentrations of 0-06 to 128 ug/ml. A phage multiple inoculator was used to inoculate approximately 10s organisms into each drug incorporated plate. The minimum inhibitory concentrations (MICs) were read after overnight incubation at 37°C. For the pharmacology experiments the subjects were ambulatory healthy young volunteers, 21 to 29 (mean 25) years old and weighing 54 to 80 (mean 66) kg. Each subject received 250 gm tetracycline ("Achromycin", Lederle) in a film coated tablet and 1 week later 200 mg minocycline as two film coated tablets (Lederle). The doses were given after an overnight fast and breakfast was taken 1 h later. Blood specimens for antibiotic levels were taken at quarter hourly intervals for the first hour and then at 90 min, 2, 3, 6, 8 and 24 h for tetracycline and 90 min, 2, 4, 8 and 24 h for minocycline. The total amount of urine passed during the 24 h after drug administration was collected. The serum and urine levels of minocycline and tetracycline were determined by a modification of the method recommended by Cyanamid International (Technical publications RL 02387 and RLA 10239). Estimations were carried out by an agar plate diffusion assay using DST agar (Oxoid) and Bacillus cereus NC1B 8849 as the test organism. Serum standards were prepared in pooled human serum and phosphate buffer, pH 4-5, to give a final concentration range of 0-0375 to 0-3 ug/ml for minocycline and 0-1 to 5 ug/ml for tetracycline. The same range of concentrations of both antibiotics prepared in phosphate buffer alone was used as standards for the urine estimations. Urine and serum samples were diluted in phosphate buffer, pH 4-5, using comparable amounts of serum as for the standard solutions, to an approximate concentration. Standards and samples were tested in triplicate. The plates were incubated at 30°C and the zone sizes read after 18 h. The sample concentrations were interpolated from a graph prepared by plotting the zone diameters of the standards against their concentrations on semi-logarithmic graph paper.
(a) Microbiology (1) Group A haemolytic streptococci {Figure 1). The 25 strains tested could be divided into 2 groups on the basis of their sensitivity to tetracycline. Eight strains (32 %) were fully sensitive to 1 ug tetracycline per ml; 17 strains (68%) were not inhibited by 8 ug tetracycline per ml and were considered resistant The tetracycline-sensitive strains required similar MICs of minocycline and tetracycline but in the tetracycline-resistant strains minocycline was found to be more active than tetracycline against all strains tested. However, in none of the resistant strains was the required MIC of minocycline below 4 ug/ml. (2) Streptococcus pneumoniae (Figure 2). Of the 39 strains tested 16 (41%) were resistant to tetracycline as judged by an MIC of 4 ug tetracycline per ml or more. These 16 strains were generally far more sensitive to minocycline than to tetracycline and 13 of them were inhibited by 2 ug minocycline per ml. Three strains required 8 ug/ml of minocycline for inhibition. There was also a reduction in the MIC of tetracycline-sensitive strains with minocycline and all the pneumococci tested whether "sensitive" or "resistant" were inhibited by lower concentrations of minocycline than tetracycline.
MinocycUne and respiratory patbogens
Tetracycline
325
Minocydine
64 32 16 8
2 I -
0-500 0-250 0125 0060 Group A streptococci
Figure 1. Comparison of minimum inhibitory concentrations of tetracycline and minocydine for 25 strains of Group A streptococci.
Tetrocycllne
Minocydine
Pneumococcl
Figure 2. Comparison of minimum inhibitory concentrations of tetracycline and minocydinne for 39 strains of pncumococci.
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
4 E —
M. J. Wood, W. FarreU, S. Kattan and J. D. Williams
326
Haemophilus species 24 22
•
20
Kl
Telcocycline
Minocycline
IB 16
1 '«
1
t 12
1
o
d 10 -
j
8 •
2 -
0
0125 0-5 I 2 0 0 6 0-25
Ik
A1
1ll.lll.
4 0
1
I1
4
8 16 32 64 0
_J 1
0 125 0-5 I 2 4 0 06 0-25
8 16 32 64
MIC
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
i
6 -
I IS
Figure 3. Comparison of minimum inhibitory concentrations of tetracycline and minocycline for 51 strains of Hacmophilut.
(3) Haemophilus species. Fifty-one Haemophilus strains were tested and the MICs of tetracycline ranged from 0-25 to 6-4 |ig/ml (Figure 3). Sixteen (31 %) of the strains were not inhibited by 4 ug tetracycline per ml whereas 32 strains (63 %) had MICs of 0-25 to 1-Oug/ml tetracycline. The action of minocycline on tetracycline-resistant Haemophilus was marked and in all such strains tested there was at least an eightfold reduction of the MIC of minocycline as compared with tetracycline. Forty-eight (94 %) of all the strains were inhibited by 1 ug minocycline per ml and the other 3 strains were inhibited by 2 ug/ml (Figure 3).
3-5
8
24
Figure 4. Blood levels of tetracycline in 6 subjects over 24 h following administration.
Minocydine and respiratory pathogens
327
40
Figure 5. Blood levels of minocycline in 6 subjects over 24 h following administration.
(b) Pharmacology (1) Serum. The concentrations in the serum of the two antibiotics in each of the subjects are shown in Figures 4 and 5 and the mean values in Figure 6. Minocycline reached peak values in the serum of 2-70 to 3-70 ug/ml (mean 310 ug/ml) and tetracycline 1-40 to 3-25 (mean 2-64) ug/ml. There was little overall difference in the levels attained 3 -
i2
f Meon+ s E. minocycline 0 Meon + s.E tetracycline I I
i
I
2
3
4 5 Time(h)
6
7
i B
n
L 24
Figure 6. Mean blood leveLs over a 24 h period of minocycline and tetracycline.
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
24
328
M. J. Wood, W. FarreU, S. Kattan and J. D. Williams
Discussion
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
by the drugs in the dosage administered but the half life of minocycline as measured by graphical extrapolations varied between 12 and 22 h (mean 17 h) whereas that for tetracycline ranged from 3 to 11 h (mean 7-3 h). The mean 0 to 24 h and O-oo integral concentrations for minocycline were 43-9 and 71-1 ug/h/ml-1 respectively, and for tetracycline the values were 22-9 and 23-1 ug/h/ml-1. (2) Urine. The amounts of the antibiotics excreted in the urine during the 24 h following administration were 35 to 53 % (mean 46 %) of the given dose for tetracycline and 3-5% to 5-9% (mean 4-8%) of the administered minocycline. (3) Untoward effects. No symptoms were produced by the 250 mg of tetracycline. Two subjects noticed slight nausea commencing 2 and 4 h after taking 200 mg of minocycline and lasting for 3 and 6 h, respectively. The onset of symptoms coincided with the peak blood level in each case. The level at which symptoms occurred were 31 and 3-7 ng/ml, respectively.
Tetracyclines are among the most commonly used antibiotics in this country and much of their prescription is for infections of the respiratory tract Although they have a wide antimicrobial spectrum reports indicate that strains of the common respiratory pathogens resistent to tetracycline are widespread. Resistance in haemolytic streptococci has risen dramatically since it was first observed in 1952 (Lowbury & Hurst, 1956) and although it has decreased recently in the south of England (Robertson, 1973), it is high in other areas of Great Britain (Fallon, 1973) and still presents sufficient of a problem to preclude the use of tetracycline for treating sore throats (Garrod, Lambert & O'Grady, 1973). The prescribing of tetracyclines in bronchitis, both for long-term prophylaxis and for the home treatment of acute exacerbations depends on the sensitivity of Haemophilus influenzae and Streptococcus pneumoniae to the antibiotic. These organisms are by far the commonest pathogens found in the acute and chronic forms of bronchitis (May, 1972). However, reports indicate that strains of both organisms resistant to tetracycline are now becoming increasingly prevalent. Twenty-three per cent of Strep, pneumoniae isolated from hospital infections (Percival, Armstrong & Turner, 1969) and 12% of Haemophilus influenzae strains (Williams & Andrews, 1974) have been reported as resistant to the drug. The more recently developed derivatives of tetracycline, including minocycline differ mainly in their pharmacology, so that they are longer lasting and less frequent administration is necessary. Minocycline has also been shown to be active against tetracyclineresistant staphylococci (Steigbigel et al., 1968a; Minuth et ah, 1974; Mitchell, 1974). Activity of minocycline against tetracycline-resistant group A P-haemolytic streptococci has been reported. Steigbigel et al. (1968a) found that 6 of the 63 strains tested required 12-5 to 50 ug/ml of tetracycline to inhibit but only one strain had an MIC of minocycline greater than 31 ug/ml, McGill (1974) also showed that 66% of the 33 group A strains she tested were inhibited by 1-25 ug minocycline per ml whereas only 48% of the strains were tetracycline sensitive as judged by an MIC of 2-5 ug tetracycline per ml or less. We agree that in all tetracycline-resistant strains of group A streptococci the MIC of minocycline was less than that of tetracycline (Table I). The MICs however were still greater than the serum levels which can be expected using the recommended dosage
Mlnocycline and respiratory pathogens
329
of minocycline and the usefulness of this compound in acute throat infections and other possible streptococcal infections is therefore limited. Table I Organism
Change of MIC with minocycline
Response to minocycline
Resistant Sensitive Resistant Sensitive Resistant Sensitive
Reduction Nil Reduction Reduction Reduction Nil
Resistant Sensitive Mainly sensitive Sensitive Sensitive Sensitive
Thirty-three per cent of the isolates we studied of the HaemophUus species and 41 % of the pneumococci were resistant to tetracycline (MIC ^ 4 ng/ml) and minocycline showed significant activity against these strains. In all the pneumococci studied, whether tetracycline resistant or sensitive, the MICs of minocycline were less than those of tetracycline. In a study of 25 tetracycline-resistant pneumococci Percival et al. (1969) failed to show any significant advantage with minocycline using tube titration, and Garrod, Lambert & O'Grady (19736), also reported that the increase of in vitro activity of minocycline against tetracycline for tetracycline-resistant staphylococci did not extend to the pneumococci. The present report is at variance with thesefindings,however, in that of the 16 tetracycline-resistant pneumococci studied, 13 were inhibited by 2 ug/ml minocycline, thus extending the findings of Steigbigel et al. (1968a) who showed that minocycline was more effective than tetracycline against pneumococci but who only studied tetracycline-sensitive strains. These workers also studied 15 strains of H. influenzae and found a slight advantage with minocycline as compared with tetracycline. We find, however, that the activity of minocycline against the tetracycline-resistant HaemophUus influenzae was dramatic and in all our strains the MIC of minocycline was below 2 ug/ml. The pharmacology results are similar to those of Steigbigel et al. (19686) and show that serum levels of minocycline in the range 2-00 to 400 ug/ml can be obtained using a standard loading dose of 200 ug. The finding that only 4-8 % of the administered minocycline was excreted in the urine during the first 24 h, as compared with 46% of the tetracycline confirms previous studies (Steigbigel et al., 19686; Bernard, Yin & Simon, 1971) but the reason for this remarkable difference between the two compounds is not clear. The decrease in minocycline excretion in the urine is not mirrored by any compensatory increase in faecal excretion (Steigbigel et al., 19686) and it is possible that minocycline is changed into a substance with no biological activity or that it is concentrated into body tissues and excreted over a prolonged period of time. Bernard et al. (1971) have reported detectable concentrations of minocycline in the urine of 5 of 8 subjects at up to 180 h after administration, and minocycline has been shown to be markedly more lipophilic than other tetracyclines (Rosenblatt et al., 1966) suggesting that it may be selectively concentrated into fatty tissues prior to slow excretion. It would appear that for infections due to Strep, pneumoniae and H. influenzae minocycline has microbiological advantages over tetracycline and satisfactory serum levels are obtained. Possible vestibular side effects have been reported (Williams, Laughlin & Lee, 1974)
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
Gp A Strep. Gp A Strep. Pneumococci Pneumococci H. influenzae H. influenzae
Response to tetracycline
330
M. J. Wood, W. Fan-ell, S. Rattan and J. D. Williams
Acknowledgement
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
and 2 of the 6 volunteers given 200 mg noticed slight nausea commencing several hours after administration of the antibiotic. In neither case was the symptom severe and no vertigo or dizziness was reported by the volunteers, despite the fact that all were aware of the reported side effects. These possible side effects of minocycline require further study and may be sufficient to prevent its widespread use. These studies suggest that minocycline has potential advantages over tetracycline in the treatment of acute exacerbations of early chronic bronchitis. Although there are no data on sputum levels attained by minocycline this may not be of importance as minocycline is a bacteriostatic drug and there is no advantage in achieving high sputum levels for such drugs providing the body's defence mechanisms are not impaired (May, 1973). Clinical studies on the efficacy of minocycline in eradicating tetracycline-resistant respiratory pathogens will be needed to assess the significance of the in vitro findings.
We thank Lederle Laboratories for the supplies of minocycline and tetracycline used in this study and Dr E. London for statistical advice. References
Bernard, B., Yin, E. J. & Simon, H. J. Clinical pharmacologic studies with minocycline. Journal of Clinical Pharmacology 11: 332-348 (1971). Fallon, R. J. Tetracycline-resistant beta-haemolytic streptococci. British Medical Journal iv: 300-1 (1973). Garrod, L. P., Lambert, H. P. & O'Grady, F. Antibiotic and Chemotherapy, 4th ed. Churchill Livingstone, Edinburgh and London (1973), p. 162. Lowbury, E. J. L. & Hurst, L. Atypical anaerobic forms of Streptococcus pyogenes associated with tetracycline resistance. Journal of Clinical Pathology 9: 59-65 (1956). McGill, R. E. T. Minocycline and P-haemolytic streptococci. British Medical Journal ii: 625 (1974). May, J. R. Chemotherapy of Chronic Bronchitis and Allied Disorders, 2nd edn, English Universities Press, London (1973), pp. 26-7, 29-34. Minutb, J. N., Holmes, T. M. & Musher, D. M. Activity of tetracycline, doxycycline and minocycline against methicillin-susceptible and -resistant staphylococci. Antimicrobial Agents and Chemotherapy 6: 411-4 (1974). Mitchell, A. A. B., Comparative activity of minocycline and tetracycline. British Medical Journal i: 576-7 (1974). Percival, A., Armstrong, E. C. & Turner, G. C. Increased incidence of tetracycline-resistant pneumocci in Liverpool in 1968 Lancet i: 998-1000 (1969). Robertson, M. H. Beta-haemolytic streptococci in south-west Essex with particular reference to tetracycline resistance. British Medical Journal ii: 569-71 (1965). Robertson, M. H. Tetracycline-resistant streptococci in south-west Essex: a continuing survey. British Medical Journal Hi: 349-50 (1968). Robertson, M. H. Tetracycline-resistant beta-haemolytic streptococci in south-west Essex: Decline and fall. British Medical Journal iv: 84-5 (1973). Rosenblatt, J. E., Barrett, J. E., Brodie, J. L. & Kirby, W. M. M. Comparison of in vitro activity and clinical pharmacology of doxycycline with other tetracyclines. Antimicrobial Agents and Chemotherapy 6: 134-41 (1966). Simmons, N . A. Comparative activity of minocycline and tetracycline. British Medical Journal i: 158-9(1974). Steigbigel, N. H., Reed, C. W. & Finland, M. Susceptibility of common pathogenic bacteria to seven tetracycline antibiotics in vitro. American Journal of the Medical Sciences 255: 179-95 (1968a).
Mbiocydine and respiratory pathogens
331
Steigbigel, N. H., Reed, C. W. & Finland, M. Absorption and excretion of five tetracycline analogues in normal young men. American Journal of the Medical Sciences 255: 296-312 (19686). Williams, D. N., Laughlin, L. W. & Lee, Y-H. Minocycline: Possible vestibular side effects. Lancet ii: 744-6 (1974). Williams, J. D. & Andrews, J. Sensitivity of Haemophilus influenzae to antibiotics. British MedicalJownal i: 134-7 (1974). (Manuscript accepted 12 June 1974) Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
Activity of minocycline and tetracycline against respiratory pathogens related to blood levels
Medical Unit* and Department of Medical Microbiology, The London Hospital, London E.I, England
A study was made of minocycline as a potential agent for use in respiratory tract infections. Pharmacological studies in 6 volunteers confirmed that serum levels of minocycline in the range 2-0 to 4-0 ug/ml can be obtained using a standard loading dose of 200 ng. In a cross-over study with tetracycline, minocycline showed more uniform absorption. At clinically achievable levels minocycline was more active than tetracycline against both tetracycline-sensitive and -resistant strains of Haemophilus species and Streptococcus pneumoniae. Minocycline at 2 ug/ml inhibited 96% of the 90 strains of both species. With P-haemolytic streptococci, however, the MICs of minocycline for tetracycline-resistant strains always remained above attainable blood levels. Introduction
Minocycline is an alkylated aminotetracycline which has been shown to be more effective than other tetracyclines against tetracycline-sensitive organisms but, additionally, it has activity against tetracycline-resistant and methicillin-resistant staphylococci (Steigbigel, Reed & Finland, 1968a; Minuth, Holmes & Musher, 1974), and tetracyclineresistant Proteus species (Simmons, 1974). Over recent years the emergence of tetracycline-resistant strains of respiratory pathogens, especially p-haemolytic streptococci (Robertson, 1965, 1968; Fallon, 1973), pneumococci (Percival, Armstrong & Turner, 1969) and Haemophilus influenzae (Williams & Andrews, 1974) has become increasingly apparent. The present study was designed to compare the activity of minocycline and tetracycline against the common respiratory pathogens. In addition we determined the blood levels attained after a single dose in order to assess the potential use of minocycline in the treatment of respiratory infections due to tetracycline-sensitive and tetracycline-resistant organisms. Methods
A total of 51 strains of Haemophilus species, 39 strains of pneumococci and 25 strains of group A streptococci were isolated from a variety of upper respiratory sites. Tetracycline-resistant strains were particularly selected for study. The sensitivity of the 323
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
M. J. Wood*, W. Farrell, S. Kaftan and J. D. Williams
324
M. J. Wood, W. Farrell, S. Kattan and J. D. Williams
Results
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
organisms to minocycline and tetracycline was determined by incorporating each antibiotic with DST agar (Oxoid) containing either 5 % horse blood (for group A streptococci and pneumococci) or 0 0 5 % lysed horse blood containing 10 ng/ml NAD (for Haemophilus), to give a range of final concentrations of 0-06 to 128 ug/ml. A phage multiple inoculator was used to inoculate approximately 10s organisms into each drug incorporated plate. The minimum inhibitory concentrations (MICs) were read after overnight incubation at 37°C. For the pharmacology experiments the subjects were ambulatory healthy young volunteers, 21 to 29 (mean 25) years old and weighing 54 to 80 (mean 66) kg. Each subject received 250 gm tetracycline ("Achromycin", Lederle) in a film coated tablet and 1 week later 200 mg minocycline as two film coated tablets (Lederle). The doses were given after an overnight fast and breakfast was taken 1 h later. Blood specimens for antibiotic levels were taken at quarter hourly intervals for the first hour and then at 90 min, 2, 3, 6, 8 and 24 h for tetracycline and 90 min, 2, 4, 8 and 24 h for minocycline. The total amount of urine passed during the 24 h after drug administration was collected. The serum and urine levels of minocycline and tetracycline were determined by a modification of the method recommended by Cyanamid International (Technical publications RL 02387 and RLA 10239). Estimations were carried out by an agar plate diffusion assay using DST agar (Oxoid) and Bacillus cereus NC1B 8849 as the test organism. Serum standards were prepared in pooled human serum and phosphate buffer, pH 4-5, to give a final concentration range of 0-0375 to 0-3 ug/ml for minocycline and 0-1 to 5 ug/ml for tetracycline. The same range of concentrations of both antibiotics prepared in phosphate buffer alone was used as standards for the urine estimations. Urine and serum samples were diluted in phosphate buffer, pH 4-5, using comparable amounts of serum as for the standard solutions, to an approximate concentration. Standards and samples were tested in triplicate. The plates were incubated at 30°C and the zone sizes read after 18 h. The sample concentrations were interpolated from a graph prepared by plotting the zone diameters of the standards against their concentrations on semi-logarithmic graph paper.
(a) Microbiology (1) Group A haemolytic streptococci {Figure 1). The 25 strains tested could be divided into 2 groups on the basis of their sensitivity to tetracycline. Eight strains (32 %) were fully sensitive to 1 ug tetracycline per ml; 17 strains (68%) were not inhibited by 8 ug tetracycline per ml and were considered resistant The tetracycline-sensitive strains required similar MICs of minocycline and tetracycline but in the tetracycline-resistant strains minocycline was found to be more active than tetracycline against all strains tested. However, in none of the resistant strains was the required MIC of minocycline below 4 ug/ml. (2) Streptococcus pneumoniae (Figure 2). Of the 39 strains tested 16 (41%) were resistant to tetracycline as judged by an MIC of 4 ug tetracycline per ml or more. These 16 strains were generally far more sensitive to minocycline than to tetracycline and 13 of them were inhibited by 2 ug minocycline per ml. Three strains required 8 ug/ml of minocycline for inhibition. There was also a reduction in the MIC of tetracycline-sensitive strains with minocycline and all the pneumococci tested whether "sensitive" or "resistant" were inhibited by lower concentrations of minocycline than tetracycline.
MinocycUne and respiratory patbogens
Tetracycline
325
Minocydine
64 32 16 8
2 I -
0-500 0-250 0125 0060 Group A streptococci
Figure 1. Comparison of minimum inhibitory concentrations of tetracycline and minocydine for 25 strains of Group A streptococci.
Tetrocycllne
Minocydine
Pneumococcl
Figure 2. Comparison of minimum inhibitory concentrations of tetracycline and minocydinne for 39 strains of pncumococci.
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
4 E —
M. J. Wood, W. FarreU, S. Kattan and J. D. Williams
326
Haemophilus species 24 22
•
20
Kl
Telcocycline
Minocycline
IB 16
1 '«
1
t 12
1
o
d 10 -
j
8 •
2 -
0
0125 0-5 I 2 0 0 6 0-25
Ik
A1
1ll.lll.
4 0
1
I1
4
8 16 32 64 0
_J 1
0 125 0-5 I 2 4 0 06 0-25
8 16 32 64
MIC
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
i
6 -
I IS
Figure 3. Comparison of minimum inhibitory concentrations of tetracycline and minocycline for 51 strains of Hacmophilut.
(3) Haemophilus species. Fifty-one Haemophilus strains were tested and the MICs of tetracycline ranged from 0-25 to 6-4 |ig/ml (Figure 3). Sixteen (31 %) of the strains were not inhibited by 4 ug tetracycline per ml whereas 32 strains (63 %) had MICs of 0-25 to 1-Oug/ml tetracycline. The action of minocycline on tetracycline-resistant Haemophilus was marked and in all such strains tested there was at least an eightfold reduction of the MIC of minocycline as compared with tetracycline. Forty-eight (94 %) of all the strains were inhibited by 1 ug minocycline per ml and the other 3 strains were inhibited by 2 ug/ml (Figure 3).
3-5
8
24
Figure 4. Blood levels of tetracycline in 6 subjects over 24 h following administration.
Minocydine and respiratory pathogens
327
40
Figure 5. Blood levels of minocycline in 6 subjects over 24 h following administration.
(b) Pharmacology (1) Serum. The concentrations in the serum of the two antibiotics in each of the subjects are shown in Figures 4 and 5 and the mean values in Figure 6. Minocycline reached peak values in the serum of 2-70 to 3-70 ug/ml (mean 310 ug/ml) and tetracycline 1-40 to 3-25 (mean 2-64) ug/ml. There was little overall difference in the levels attained 3 -
i2
f Meon+ s E. minocycline 0 Meon + s.E tetracycline I I
i
I
2
3
4 5 Time(h)
6
7
i B
n
L 24
Figure 6. Mean blood leveLs over a 24 h period of minocycline and tetracycline.
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
24
328
M. J. Wood, W. FarreU, S. Kattan and J. D. Williams
Discussion
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
by the drugs in the dosage administered but the half life of minocycline as measured by graphical extrapolations varied between 12 and 22 h (mean 17 h) whereas that for tetracycline ranged from 3 to 11 h (mean 7-3 h). The mean 0 to 24 h and O-oo integral concentrations for minocycline were 43-9 and 71-1 ug/h/ml-1 respectively, and for tetracycline the values were 22-9 and 23-1 ug/h/ml-1. (2) Urine. The amounts of the antibiotics excreted in the urine during the 24 h following administration were 35 to 53 % (mean 46 %) of the given dose for tetracycline and 3-5% to 5-9% (mean 4-8%) of the administered minocycline. (3) Untoward effects. No symptoms were produced by the 250 mg of tetracycline. Two subjects noticed slight nausea commencing 2 and 4 h after taking 200 mg of minocycline and lasting for 3 and 6 h, respectively. The onset of symptoms coincided with the peak blood level in each case. The level at which symptoms occurred were 31 and 3-7 ng/ml, respectively.
Tetracyclines are among the most commonly used antibiotics in this country and much of their prescription is for infections of the respiratory tract Although they have a wide antimicrobial spectrum reports indicate that strains of the common respiratory pathogens resistent to tetracycline are widespread. Resistance in haemolytic streptococci has risen dramatically since it was first observed in 1952 (Lowbury & Hurst, 1956) and although it has decreased recently in the south of England (Robertson, 1973), it is high in other areas of Great Britain (Fallon, 1973) and still presents sufficient of a problem to preclude the use of tetracycline for treating sore throats (Garrod, Lambert & O'Grady, 1973). The prescribing of tetracyclines in bronchitis, both for long-term prophylaxis and for the home treatment of acute exacerbations depends on the sensitivity of Haemophilus influenzae and Streptococcus pneumoniae to the antibiotic. These organisms are by far the commonest pathogens found in the acute and chronic forms of bronchitis (May, 1972). However, reports indicate that strains of both organisms resistant to tetracycline are now becoming increasingly prevalent. Twenty-three per cent of Strep, pneumoniae isolated from hospital infections (Percival, Armstrong & Turner, 1969) and 12% of Haemophilus influenzae strains (Williams & Andrews, 1974) have been reported as resistant to the drug. The more recently developed derivatives of tetracycline, including minocycline differ mainly in their pharmacology, so that they are longer lasting and less frequent administration is necessary. Minocycline has also been shown to be active against tetracyclineresistant staphylococci (Steigbigel et al., 1968a; Minuth et ah, 1974; Mitchell, 1974). Activity of minocycline against tetracycline-resistant group A P-haemolytic streptococci has been reported. Steigbigel et al. (1968a) found that 6 of the 63 strains tested required 12-5 to 50 ug/ml of tetracycline to inhibit but only one strain had an MIC of minocycline greater than 31 ug/ml, McGill (1974) also showed that 66% of the 33 group A strains she tested were inhibited by 1-25 ug minocycline per ml whereas only 48% of the strains were tetracycline sensitive as judged by an MIC of 2-5 ug tetracycline per ml or less. We agree that in all tetracycline-resistant strains of group A streptococci the MIC of minocycline was less than that of tetracycline (Table I). The MICs however were still greater than the serum levels which can be expected using the recommended dosage
Mlnocycline and respiratory pathogens
329
of minocycline and the usefulness of this compound in acute throat infections and other possible streptococcal infections is therefore limited. Table I Organism
Change of MIC with minocycline
Response to minocycline
Resistant Sensitive Resistant Sensitive Resistant Sensitive
Reduction Nil Reduction Reduction Reduction Nil
Resistant Sensitive Mainly sensitive Sensitive Sensitive Sensitive
Thirty-three per cent of the isolates we studied of the HaemophUus species and 41 % of the pneumococci were resistant to tetracycline (MIC ^ 4 ng/ml) and minocycline showed significant activity against these strains. In all the pneumococci studied, whether tetracycline resistant or sensitive, the MICs of minocycline were less than those of tetracycline. In a study of 25 tetracycline-resistant pneumococci Percival et al. (1969) failed to show any significant advantage with minocycline using tube titration, and Garrod, Lambert & O'Grady (19736), also reported that the increase of in vitro activity of minocycline against tetracycline for tetracycline-resistant staphylococci did not extend to the pneumococci. The present report is at variance with thesefindings,however, in that of the 16 tetracycline-resistant pneumococci studied, 13 were inhibited by 2 ug/ml minocycline, thus extending the findings of Steigbigel et al. (1968a) who showed that minocycline was more effective than tetracycline against pneumococci but who only studied tetracycline-sensitive strains. These workers also studied 15 strains of H. influenzae and found a slight advantage with minocycline as compared with tetracycline. We find, however, that the activity of minocycline against the tetracycline-resistant HaemophUus influenzae was dramatic and in all our strains the MIC of minocycline was below 2 ug/ml. The pharmacology results are similar to those of Steigbigel et al. (19686) and show that serum levels of minocycline in the range 2-00 to 400 ug/ml can be obtained using a standard loading dose of 200 ug. The finding that only 4-8 % of the administered minocycline was excreted in the urine during the first 24 h, as compared with 46% of the tetracycline confirms previous studies (Steigbigel et al., 19686; Bernard, Yin & Simon, 1971) but the reason for this remarkable difference between the two compounds is not clear. The decrease in minocycline excretion in the urine is not mirrored by any compensatory increase in faecal excretion (Steigbigel et al., 19686) and it is possible that minocycline is changed into a substance with no biological activity or that it is concentrated into body tissues and excreted over a prolonged period of time. Bernard et al. (1971) have reported detectable concentrations of minocycline in the urine of 5 of 8 subjects at up to 180 h after administration, and minocycline has been shown to be markedly more lipophilic than other tetracyclines (Rosenblatt et al., 1966) suggesting that it may be selectively concentrated into fatty tissues prior to slow excretion. It would appear that for infections due to Strep, pneumoniae and H. influenzae minocycline has microbiological advantages over tetracycline and satisfactory serum levels are obtained. Possible vestibular side effects have been reported (Williams, Laughlin & Lee, 1974)
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
Gp A Strep. Gp A Strep. Pneumococci Pneumococci H. influenzae H. influenzae
Response to tetracycline
330
M. J. Wood, W. Fan-ell, S. Rattan and J. D. Williams
Acknowledgement
Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
and 2 of the 6 volunteers given 200 mg noticed slight nausea commencing several hours after administration of the antibiotic. In neither case was the symptom severe and no vertigo or dizziness was reported by the volunteers, despite the fact that all were aware of the reported side effects. These possible side effects of minocycline require further study and may be sufficient to prevent its widespread use. These studies suggest that minocycline has potential advantages over tetracycline in the treatment of acute exacerbations of early chronic bronchitis. Although there are no data on sputum levels attained by minocycline this may not be of importance as minocycline is a bacteriostatic drug and there is no advantage in achieving high sputum levels for such drugs providing the body's defence mechanisms are not impaired (May, 1973). Clinical studies on the efficacy of minocycline in eradicating tetracycline-resistant respiratory pathogens will be needed to assess the significance of the in vitro findings.
We thank Lederle Laboratories for the supplies of minocycline and tetracycline used in this study and Dr E. London for statistical advice. References
Bernard, B., Yin, E. J. & Simon, H. J. Clinical pharmacologic studies with minocycline. Journal of Clinical Pharmacology 11: 332-348 (1971). Fallon, R. J. Tetracycline-resistant beta-haemolytic streptococci. British Medical Journal iv: 300-1 (1973). Garrod, L. P., Lambert, H. P. & O'Grady, F. Antibiotic and Chemotherapy, 4th ed. Churchill Livingstone, Edinburgh and London (1973), p. 162. Lowbury, E. J. L. & Hurst, L. Atypical anaerobic forms of Streptococcus pyogenes associated with tetracycline resistance. Journal of Clinical Pathology 9: 59-65 (1956). McGill, R. E. T. Minocycline and P-haemolytic streptococci. British Medical Journal ii: 625 (1974). May, J. R. Chemotherapy of Chronic Bronchitis and Allied Disorders, 2nd edn, English Universities Press, London (1973), pp. 26-7, 29-34. Minutb, J. N., Holmes, T. M. & Musher, D. M. Activity of tetracycline, doxycycline and minocycline against methicillin-susceptible and -resistant staphylococci. Antimicrobial Agents and Chemotherapy 6: 411-4 (1974). Mitchell, A. A. B., Comparative activity of minocycline and tetracycline. British Medical Journal i: 576-7 (1974). Percival, A., Armstrong, E. C. & Turner, G. C. Increased incidence of tetracycline-resistant pneumocci in Liverpool in 1968 Lancet i: 998-1000 (1969). Robertson, M. H. Beta-haemolytic streptococci in south-west Essex with particular reference to tetracycline resistance. British Medical Journal ii: 569-71 (1965). Robertson, M. H. Tetracycline-resistant streptococci in south-west Essex: a continuing survey. British Medical Journal Hi: 349-50 (1968). Robertson, M. H. Tetracycline-resistant beta-haemolytic streptococci in south-west Essex: Decline and fall. British Medical Journal iv: 84-5 (1973). Rosenblatt, J. E., Barrett, J. E., Brodie, J. L. & Kirby, W. M. M. Comparison of in vitro activity and clinical pharmacology of doxycycline with other tetracyclines. Antimicrobial Agents and Chemotherapy 6: 134-41 (1966). Simmons, N . A. Comparative activity of minocycline and tetracycline. British Medical Journal i: 158-9(1974). Steigbigel, N. H., Reed, C. W. & Finland, M. Susceptibility of common pathogenic bacteria to seven tetracycline antibiotics in vitro. American Journal of the Medical Sciences 255: 179-95 (1968a).
Mbiocydine and respiratory pathogens
331
Steigbigel, N. H., Reed, C. W. & Finland, M. Absorption and excretion of five tetracycline analogues in normal young men. American Journal of the Medical Sciences 255: 296-312 (19686). Williams, D. N., Laughlin, L. W. & Lee, Y-H. Minocycline: Possible vestibular side effects. Lancet ii: 744-6 (1974). Williams, J. D. & Andrews, J. Sensitivity of Haemophilus influenzae to antibiotics. British MedicalJownal i: 134-7 (1974). (Manuscript accepted 12 June 1974) Downloaded from http://jac.oxfordjournals.org/ at The University of British Colombia Library on November 26, 2014
