Susceptibility of common pathogenic bacteria to seven tetracycline antibiotics in vitro

A Comparative Trial of Minocin (Minocycline Hydrochloride) and Ampicillin in the Treatment of Acute Exacerbations of Chronic Bronchitis

One hundred and fifteen patients suffering from acute exacerbations of chronic bronchitis took part in a double-blind, multicentre, clinical trial designed to compare the therapeutic efficacy and tolerability of ampicillin and minocycline hydrochloride, a new, long-acting, semi-synthetic tetracycline.

Both antibiotics were equally successful in treatment, there being no statistically significant difference between the two in any of the parameters studied.

Side-effects were few and far between. Only one patient out of the 57 who took minocycline, complained of dizziness.

Pharmacokinetics of minocycline in domestic cats

OBJECTIVES

Recently, the increased cost and decreased availability of doxycycline has sparked an interest in using minocycline as an alternative. The purpose of this study was to determine the pharmacokinetics of minocycline in domestic cats in order to facilitate dosage decisions.

METHODS

Purpose-bred, young adult cats were administered a single dose of either intravenous (IV; n = 4; 5 mg/kg) or oral (n = 6; 50 mg/cat) minocycline. Blood was collected from each at intervals up to 24 h afterwards. Minocycline was measured using high performance liquid chromatography with ultraviolet detection. A one-compartment pharmacokinetic model was fit to the oral data and a two-compartment model to the IV data via a computer program. Plasma protein binding was measured by fortifying blank plasma from untreated healthy cats with minocycline at two concentrations and applying an ultracentrifugation method.

RESULTS

Two cats became transiently lethargic and tachypneic during IV drug infusion. One cat vomited 6.0 h after infusion, and two cats vomited either 1.5 h or ~5.0 h after oral drug administration. The mean oral dose administered was 13.9 ± 0.47 mg/kg. Oral bioavailability was approximately 62%. Plasma protein binding was 60% at 5 µg/ml and 46% at 1 μg/ml. After IV administration, elimination half-life (t(½)), apparent volume of distribution at steady-state, and systemic clearance were 6.7 h (coefficient of variation [CV] 14.4%), 1.5 l/kg (CV 34.5%) and 2.9 ml/kg/min (CV 40.8%), respectively. After oral administration the terminal t(½) and peak concentration (Cmax) were 6.3 h (CV 9%) and 4.77 µg/ml (CV 36%), respectively.

CONCLUSIONS AND RELEVANCE

Because most bacteria will have a minimum inhibitory concentration of ⩽0.5 μg/ml, an oral dose of 8.8 mg/kg q24h would be adequate to meet pharmacokinetic-pharmacodynamic targets after adjusting for protein binding. Although some gastrointestinal upset may occur, one 50 mg capsule orally q24h would provide appropriate dosing for most cats.

Minocycline: old and new therapeutic uses

Since the introduction of minocycline HCl in the late 1960's, it has been used for disease states that have ranged from typical community-acquired infectious diseases to others that are non-infectious, such as resistant rheumatoid arthritis. Owing to its high penetration characteristics throughout the body, minocycline can be used in the treatment of a wide variety of extracellular and intracellular pathogens. This review examines the known and potential therapeutic uses of minocycline in a clinical setting.

Susceptibility of Staphylococci to Minocycline In Vitro: Identification of Group III Bacteriophage Types by Characteristic Inhibition of Growth

Minocycline in concentrations of 1.0 mug per ml or less inhibited growth of 50 staphylococcal isolates which were tested by the broth dilution method. All strains were resistant to penicillin and tetracycline, and 34% were resistant to lincomycin. Minocycline discs identified two populations of minocycline-susceptible strains. The first group with small zones of inhibition surrounding the disc had multiple resistance and all were lysed by group III phage (84/85). The organisms with larger diameter of zones of inhibition were less frequently resistant to the antibiotics tested, and only 7.4% of these organisms were lysed by the 84/85 phage.

Antibiotics in the management of pediatric skin disease

An increasingly large number of antibiotics are available for the treatment of uncomplicated skin and skin structure infections in children. Primary factors in the choice among these agents are the antibiotic resistance profile of the target pathogen(s), and the antibiotic's spectrum of activity, pharmacologic properties, potential adverse reactions and interactions and propensity to select for the emergence of resistant organisms. Based on a consideration of these principles, this article provides a practical guide to the use of antibiotics in the management of common cutaneous infections in the pediatric population.

Minocycline versus vancomycin for treatment of experimental endocarditis caused by oxacillin-resistant Staphylococcus aureus

The purpose of this study was to determine the penetration of minocycline and vancomycin into cardiac vegetations and to determine their efficacy in a rabbit model of endocarditis caused by oxacillin-resistant Staphylococcus aureus. Animals were randomized into three groups: control (no antibiotic), minocycline (6 mg/kg given intravenously every 8 h), and vancomycin (50 mg/kg given intravenously every 8 h). Penetration of the antibiotics into aortic valve vegetations was determined by using the tissue/serum area under the concentration-time curve ratio. The reductions in the bacterial density of the vegetations caused by both vancomycin (4.8 +/- 1.2 CFU/g) and minocycline (5.3 +/- 1.6 CFU/g) were significantly different from that of controls (8.7 +/- 1.8 CFU/g). Although the penetration of minocycline was twice that of vancomycin, they were equally effective in reducing the bacterial density of the vegetations, since the concentrations of both agents in tissue remained above their MICs for oxacillin-resistant S. aureus. For organisms for which the MICs are higher, however, these penetration differences may result in treatment differences.

Susceptibility and resistance of plaque bacteria to minocycline

The in vitro susceptibility of 55 strains of subgingival plaque bacteria to minocycline was determined. A concentration of 1 microgram/ml minocycline was found to inhibit 85% of the strains tested and the MIC ranged from 0.03 to 32 micrograms/ml. For 71% of the strains tested the MBC was at least 4 times greater than the corresponding MIC, suggesting a bacteriostatic activity for minocycline. A concentration of 20 mg/ml of magnesium ions was capable of neutralizing 8 micrograms/ml of minocycline and was used to eliminate "carry-over" effects inherent in the experimental procedure. After 6 to 7 weeks exposure to sub-lethal concentrations of minocycline there was no appreciable increase in the MICs of most organisms with the exception of Actinobacillus actinomycetemcomitans NCTC 10981 and Campylobacter concisus NCTC 11485. Short term (6 hour exposure of bacteria to minocycline (8 micrograms/ml) markedly reduced the viability of a number of periodontopathogens but had little effect on the viability of Veillonella parvula NCTC 11456 and Fusobacterium nucleatum NCTC 11326. These in vitro investigations have demonstrated that minocycline is capable of inhibiting most of the periodontitis-associated bacteria tested and can kill some of these bacteria after a comparatively short exposure time. However, some of the organisms tested exhibited a low susceptibility to minocycline and others became less susceptible following exposure to low concentrations of the antibiotic for several weeks.

Endocarditis caused by relatively penicillin-resistant Stomatococcus mucilaginosus

We report a case of Stomatococcus mucilaginosus endocarditis in which the isolate was relatively resistant to penicillins and cephalothin. The patient was treated successfully with vancomycin and valve replacement.

Ten-year computerized audit of infection after abdominal surgery

A prospective audit of the frequency of infective complications after all abdominal operations was carried out between January 1977 and December 1986. A total of 3100 abdominal procedures (2041 elective; 1059 emergency) were performed in 3056 patients. There were 50 (1.6 per cent) in-hospital and 66 (2.1 per cent) late wound infections (overall 3.7 per cent). Fifty-four (1.8 per cent) patients developed postoperative intraperitoneal sepsis. Ninety-eight patients died (overall mortality 3.2 per cent) and intraperitoneal sepsis was a related factor in twelve (0.4 per cent). Wound infection, peritoneal sepsis and mortality were related to the degree of operative contamination and to reoperation. The results support the traditional, although sometimes inadequately stressed, teaching that technique is an important factor in preventing infection. Infection is also reduced by peroperative antibiotic lavage. The limited value and the potential difficulties of the unstructured introduction of computerized audit should be recognized.

Effect of topical and systemic antibiotics on bacterial growth kinesis in generalized peritonitis in man

Quantitative bacteriology in peritoneal exudate was studied in 40 patients with generalized peritonitis of small intestinal, appendicular or colonic origin. Bacterial growth kinesis was measured in 28 of the patients. Systemic antibiotics given before operation resulted in a significant reduction in both the concentration and growth rate of viable bacteria in the peritoneal fluid. Lavage of the peritoneal cavity with saline resulted in a further reduction in growth rate in patients given pre-operative systemic antibiotics by an effect attributable to simple dilution. In contrast, peritoneal lavage with tetracycline (1 mg/ml) resulted in complete inhibition of bacterial growth in the residual peritoneal fluid. These observations support the policy of giving systemic antibiotics to patients with generalized peritonitis as soon as the diagnosis has been made and provide bacteriological evidence for the value of peroperative antibiotic peritoneal lavage.

Antibiotic prophylaxis in non-perforated appendicitis of childhood: tetracycline lavage compared with peroperative intravenous cefuroxime and metronidazole

Eighty-four cases of non-perforated appendicitis in children were randomly allocated to receive either oxytetracycline lavage alone or oxytetracycline lavage plus peroperative intravenous metronidazole and cefuroxime. The wound infection rate with the oxytetracycline lavage alone was 4.4% compared with 7.7% when metronidazole and cefuroxime were added. These rates were not significantly different. This study supports the use of oxytetracycline lavage alone as effective prophylaxis against wound infection in non-perforated appendicitis of childhood.

The effect of peritoneal lavage with tetracycline solution on postoperative infection. A prospective, randomized, clinical trial

A prospective randomized trial was performed to determine the value of tetracycline lavage in addition to systemic antibiotic prophylaxis in 159 patients undergoing elective and emergency intestinal operations. Tetracycline lavage was associated with a significant overall reduction in postoperative infection rates in 25 of 74 patients (34 percent) receiving saline lavage compared with 15 of 85 patients (18 percent) having tetracycline lavage (P less than 0.05). Tetracycline lavage was associated with a significant reduction in the counts of aerobic and anaerobic bacteria in the peritoneal fluid at the end of the operation (P less than 0.05 and P less than 0.01, respectively) and with a significant reduction of aerobes 24 hours postoperatively (P less than 0.02). Tetracycline lavage would appear to confer clinical benefit in preventing postoperative infection.

Infection after abdominal surgery: five year prospective study

A total of 1504 consecutive abdominal operations were studied prospectively over a five year period. The incidence of wound (2.8%) and intraperitoneal (0.8%) infections was low compared with contemporary reports. It is difficult to justify modifying existing practice on the basis of small controlled clinical trials when information from accurate audit discloses results superior to those of experimental studies.

Haemophilus influenzae, Pneumococci, group A streptococci and Staphylococcus aureus: sensitivity of outpatient strains to commonly prescribed antibiotics

The degree of resistance of Haemophilus influenzae, pneumococci, group A streptococci and Staphylococcus aureus to phenoxymethylpenicillin, ampicillin, doxycycline, erythromycin and chloramphenicol was investigated with the MIC-method (plate-dilution technique). Each bacterial group consisted of 100 outpatient strains. Seven strains of H. influenzae were beta-lactamase-producing. Of the 100 haemophilus strains, 58% were sensitive and the rest intermediate sensitive to erythromycin. 99% were sensitive to doxycycline and all strains were sensitive to chloramphenicol. Essentially all pneumococcal strains were sensitive to the antibiotics tested. However, a few strains demonstrated diminished sensitivity to penicillins. All group A streptococci were sensitive to ampicillin, penicillin and chloramphenicol, and 98% were sensitive to erythromycin. Approximately 1 strain out of 5 was resistant to doxycycline. 75% of S. aureus were beta-lactamase producers. Four of the S., aureus strains were resistant to erythromycin and 8 to doxycycline. The results presented indicate a better antibiotic situation than in some other countries, but suggest the need for a more extensive antibiotic sensitivity examination of isolated bacteria.

The tetracyclines

Tetracyclines continue to be used extensively on a world-wide basis because of their unusually broad antimicrobial spectrum and their relative safety. The first generation tetracyclines are used almost exclusively via the oral route; the second generation tetracyclines may be used orally or intravenously. Intramuscular administration is not recommended. Doxycycline is preferred in the treatment of upper respiratory tract infections, atypical pneumonias, intraabdominal/pelvic sepsis or trauma, venereal diseases, and in the treatment of prostatitis. Minocycline is preferred for meningococcal prophylaxis, central nervous system infections (due to susceptible organisms), and in staphylococcal infections (when tetracycline is indicated).

Liquid chromatographic determination of minocycline in human serum

A rapid, specific, and sensitive liquid chromatographic assay for minocycline in human serum is described. The drug and an internal standard (oxytetracycline) were extracted into ethyl acetate from 0.5 ml of buffered serum (pH 6.5). Chromatographic separation was achieved on a 10-micrometer Lichrospher 100 CH 8 column with acetonitrile--citric acid (0.1 M) as the eluent. The column effluent was monitored at 352 nm. The assay was linear up to 3 micrograms/ml with a mean coefficient of variation of 3.3% (n = 6). An extraction recovery of 89.4 +/- 3.2% (mean +/- SD, n = 17) was obtained over the 0.5--2.6 micrograms/ml range. The detection limit averaged 50 ng/ml. A serum concentration-time profile in humans after oral intake is presented.

Minocycline diffusion into benign prostatic hyperplasia

Minocycline, a broad-spectrum, highly lipid soluble tetracycline that has generated interest in the treatment of chronic prostatitis, was evaluated for its possible ability to be concentrated in benign prostatic hyperplasia. Drug levels in the prostate, plasma, fat, muscle and urine were measured in patients undergoing open prostatectomy after preoperative intravenous minocycline. The concentrations of the drug in the prostate and serum were close (4.16 versus 3.01 microgram. per gm.), while drug levels in striated muscle and fat were consistently lower (2.92 and 0.77 microgram. per gm). Higher preoperative doses of drug yielded higher tissue levels. Drug delivery closer temporally to the operation yielded higher serum and prostatic levels as opposed to striated muscle and fat, suggesting a rapid diffusion of the drug into benign prostatic hyperplasia.

Sensitivity of Brucella spp to tetracycline and its analogues

The sensitivity to eight tetracyclines of 100 strains of brucellae, comprising strains of Brucella abortus, Br. melitensis, and Br. suis, was determined. Demethylchlortetracycline was the most effecitve against all the groups of brucellae, whereas oxytetracycline and chlortetracycline were the least effective. The mean MIC value for demethylchlortetracycline, doxycycline, lymecycline, and tetracycline was less than or equal to 1 mug/ml. Strains of Br. abortus biotype 2 and Br. suis were the most sensitive strains examined.

The penetration of minocycline into human sinus secretions

The mean minocycline content of sinus secretions aspirated during antral wash-out in 8 patients sinusitis was found to be 1.06 mug. per ml. (SD.1.03). This exceeds the M.I.C. for most strains of bacteria likely to be found in sinusitis. The mean minocycline serum level in these 8 patients was 3.16 mug. per ml. (S.D. 1.64). The sinus secretion to serum level ratio was therefore 0.34:1. No correlation was found between serum level and sinus secretion level, nor could any of the factors looked at in this study be correlated with the degree to which minocycline penetrated the sinus secretion.

Susceptibility of Acinetobacter calcoaceticus var. anitratus (Herellea vaginicola) to minocycline

The in vitro activity of minocycline against Acinetobacter calcoaceticus var. anitratus (Herellea vaginicola) was examined. All strains of A. anitratus were inhibited by minocycline at concentrations of 0.4 mug/ml or less. The strains studied were considerably more susceptible to minocycline than tetracycline. No difference between the susceptibility to minocycline and tetracycline was seen with Escherichia coli, Klebsiella pneumoniae, Enterobacter and Proteus sp. A regression line of the log minimal inhibitory concentration (MIC) values and the diameter of the zone of inhibition, determined by the Kirby-Bauer technique, showed good linear correlation for minocycline. Comparison of the disk diffusion results and MICs indicated that an inhibitory zone size of 19 mm produced by a 30-mug minocycline disk was equivalent to a MIC of 3.1 mug/ml, a serum concentration achieved by oral administration of the drug. When the zone of inhibition was greater than 19 mm, however, there was poor correlation with the MIC for Enterobacteriaceae.

Prevention of infection during transrectal biopsy of prostate through double-glove technique

Eighty male patients, most of whom had suspicious prostatic nodules on digital examination, were subjected to transrectal needle biopsy of the prostate. The biopsy needle was held between the gloved hand and an overlying sterile finger cot on the index finger. When the lesion was palpated, the needle was pushed through the finger cot and a tissue specimen obtained. All patients were treated orally with minocycline hydrochloride 100 mg. twice a day starting eight to twelve hours before biopsy and continuing at this dosage for five days after biopsy. Except for one episode of transitory hematuria, there were no reports of infection or complication, as manifested by fever, chills, or transrectal or transurethral bleeding.

Susceptibility of pneumococci and Haemophilus influenzae to antibacterial agents

Strains of Diplococcus pneumoniae and Haemophilus influenzae were tested for susceptibility to numerous antibiotics by a twofold agar dilution method using an inocula replicator. Undiluted, fully grown broth cultures were used as inocula for both species, and cultures of pneumococci diluted 1:1,000 were also tested. The antibiotics included most of those in common use in the United States as well as some chemical modifications recently approved and others that are under investigation. The most striking aspect of the results was the marked susceptibility of the pneumococci to all the antibiotics tested except the polymyxins and most of the aminoglycoside antibiotics, although some new aminoglycosides were active in quite low concentrations. Some of the strains of pneumococci were of decreased susceptibility to penicillin G (minimal inhibitory concentrations, 0.2 to 0.4 mug/ml), but none were tetracycline resistant, although such strains had been reported previously from this laboratory. The strains of H. influenzae, which were all serologically nontypable, exhibited different patterns of susceptibility to the groups of antibiotics and to the individual chemically related ones. None of these strains (isolated early in 1972) were ampicillin resistant. The most active agents against H. influenzae were: carbenicillin and ampicillin, analogues related to each of them, rifampin, chloramphenicol, and the polymyxins. However, the tetracycline analogues other than tetracycline, some aminoglycosides, notably tobramycin, kanamycin, gentamicin, and verdamicin, erythromycin, and some new lincomycin analogues were also active in low concentrations. Trimethoprim alone was highly active, and in combination with sulfamethoxazole it was even more active and synergistic against strains of both D. pneumoniae and H. influenzae.

Minocycline hydrochloride (Minocin) as a single-dose oral treatment of uncomplicated gonorrhoea in men

349 male patients with uncomplicated gonococcal urethritis were treated with a single dose of 300 mg. or 400 mg. minocycline hydrochloride. The lower dose gave a lower failure rate, 3-2 compared with 5-1 per cent., but this difference was not statistically significant. The overall known failure rate of 4-2 per cent. compares most favourably with our previous findings in this area using other drugs of the tetracycline group. The incidence of post-gonococcal urethritis (5-1 per cent.) was also the lowest we have found. The few side-effects reported were comparatively trivial. Because of its high degree of therapeutic efficacy, the relatively lack of side-effects, and the reduced incidence of post-gonococcal urethritis, minocycline hydrochloride should be considered the drug of choice whenever single-dose oral treatment is given in uncomplicated gonorrhoea in men.

Interactions with the absorption of tetracyclines

All tetracycline derivatives are bacteriostatics and their concentration in serum should not fall during the therapy below the generally accepted minimum therapeutic concentration of 0.5 to 1.5 mug/ml. Tetracyclines have a high affinity to form chelates with polyvalent metallic cations such as Fe+++, Fe++, Al+++, Mg++ and Ca++. Many of these tetracycline-metal complexes are either insoluble or otherwise poorly absorbable from the gastro-intestinal tract. Milk and other dairy products, antacids containing polyvalent cations, as well as various iron salts ingested simultaneously with tetracycline derivatives, might interfere with their absorption by 50 to 90% or even more. The severity of interaction depends both on the nature of the tetracycline derivative and of the cation, on the doses used, on pharmaceutical factors, and on time schedules in dosing. An interval of 3 hours between the ingestion of tetracyclines and cations prevents the interaction. The pharmacokinetic interactions in absorption of tetracyclines likely to be clinically significant in cases where the infecting pathogens are moderately resistant to tetracyclines and relatively high serum concentrations are needed for proper bacteriostasis.

Relation between lipophilicity and pharmacological behavior of minocycline, doxycycline, tetracycline, and oxytetracycline in dogs

Four tetracyclines were studied in dogs to determine the relation between their lipophilicity and various other pharmacological characteristics. Lipid solubility correlated inversely with the mean concentration of drug in arterial plasma and renal uptake and excretion, and directly with the biliary concentration gradient (level in bile/level of free drug in serum). Only the more lipophilic congeners minocycline and doxycycline passed the blood-brain and blood-ocular barriers in detectable concentrations. Mean levels of minocycline in the brain exceeded those of doxycycline by almost threefold; the difference was of borderline statistical significance (P = 0.05 to 0.1). Lipophilicity correlated inversely with the concentration of antibiotic in renal medulla but not in renal cortex or in the liver. When intestinal loops containing saline, milk, or 10% Gelusil were studied, the only combination exhibiting striking intraluminal accumulation was doxycycline in milk. These results indicate that lipophilicity correlates with many, but not all, of the transport characteristics of tetracycline antibiotics.

Evaluation of the antibiotic effect of treatment of maxillary sinusitis

As the effect of antibiotic treatment of maxillary sinusitis has been questioned, the elimination of bacteria from sinus secretions was studied during antibiotic treatment. Penicillin V, azidocillin, tetracycline or doxycycline was administered to 54 patients with maxillary sinusitis. Samples of sinus secretion were aspirated both before treatment and 2-3 days after the onset of treatment. When the antibiotic concentration was below the upper limit of MIC for sensitivity group 1, bacterial growth was present in practically all samples. When the antibiotic concentration equalled or was above this limit, there was no bacterial growth in about half of the samples. A prerequisite for antibiotic effect--elimination of bacteria--is that the antibiotic concentration is well above the MIC of the bacteria at the site of infection. The choice between bactericidal or bacteriostatic antibiotics appeared unimportant. Bacterial survival in the maxillary sinus despite a high antibiotic concentration in the sinus illustrates that MIC values determined in the laboratory do not always mirror the sensitivity of bacteria to antibiotics in vivo.

Pharmacokinetics of minocycline in renal failure

The pharmacokinetics of minocycline have been studied after single intravenous infusions and repeated oral doses to human subjects with varying degrees of renal impairment. There was no evidence of reduced drug clearance with reduced renal function after intravenous doses although there appeared to be an increase in the tissue distribution of antibiotic in the body in uremia. After identical multiple oral dosage regimens serum levels of antibiotic were comparable in normal and mildly uremic subjects. There was no evidence of renal toxicity in normal or uremic subjects with the repeated dosage regimen used.

Hemolysin production in Escherichia coli associated with nalidixic acid resistance

The activity of minocycline and tetracycline against 23 isolates of Acinetobacter calcoaceticus var. anitratus (syn. Herellea vaginicola) and 178 strains of Serratia marcescens was determined by disk and microdilution methods. The results indicate that minocycline is highly active against this species of Acinetobacter, all but one strain being inhibited by 0.007 μg of the antibiotic per ml. Tetracycline was also active, though to a lesser degree, against A. calcoaceticus. Of the 178 strains of S. marcescens tested, only seven (3.9%) had a minimum inhibitory concentration of 2 μg or less of minocycline per ml. Tetracycline was less active than minocycline against S. marcescens; with 2 μg of tetracycline per ml, only 2 of 152 (1.3%) strains were inhibited. At concentrations of 8 and 16 μg of minocycline per ml, which can be achieved in the urine with the usual doses, 44.9 and 63.5% of S. marcescens strains were inhibited, which implies its possible usefulness for the therapy of urinary tract infection due to this organism.

Differences in susceptibility of Enterobacteriaceae and penicillin-resistant Staphylococcus aureus to tetracycline and minocycline

Two hundred strains of penicillin-resistant Staphylococcus aureus and 311 isolates of Enterobacteriaceae were compared for their susceptibility to tetracycline and minocycline. Thirteen and one-half percent of the staphylococcal isolates were resistant to tetracycline but susceptible to minocycline. Similarly, 24% of the enterobacterial isolates were found to be tetracycline resistant but susceptible to minocycline. Of a total of 511 recent clinical isolates, 14.5% were susceptible to minocycline but were tetracycline resistant.

Acute pelvic inflammatory disease and clinical response to parenteral doxycycline

The bacteriology of acute pelvic inflammatory disease (PID) and clinical response to parenteral doxycycline were evaluated in 30 patients. Only 3 of 21 cul-de-sac cultures from PID patients were sterile, whereas all 8 normal control subjects yielded negative results (P< 0.005). Poor correlation was observed between cervical and cul-de-sac cultures. Neisseria gonorrhoeae, isolated from the cervix in 17 patients (57%), was recovered from the cul-de-sac only once. Streptococcus, Peptococcus, Peptostreptococcus, coliforms, and other organisms normally present in the vagina were the predominant isolates recovered from the cul-de-sac. Parenteral doxycycline resulted in rapid resolution of signs and symptoms (within 48 h) in 20 of 27 evaluable patients (74%). In five others, signs and symptoms of infection abated within 4 days. The remaining two patients failed to respond; in both cases, adnexal masses developed during doxycycline therapy. Gonococci were eradicated from the cervix in all but one patient who, nevertheless, had a rapid defervescence of symptoms. There was no clear-cut correlation between the clinical response and in vitro susceptibility of cul-de-sac isolates to doxycycline. These data confirm the usefulness of broad-spectrum antibiotics in acute PID. Culdocentesis is a reliable means of obtaining material for the bacteriological diagnosis of acute PID; however, the pathogenetic role and relative importance of gonococci and various other bacteria in acute PID need to be clarified further.

Minocycline: A review of its antibacterial and pharmacokinetic properties and therapeutic use

Minocycline is a semi-synthetic tetracycline derivative which is well absorbed and distributed in body tissues and is suitable for twice daily administration. It appears to be as generally effective as other tetracyclines and analogues, but also to be effective in infections due to tetracycline-resistant staphylococci. Side-effects are typical of those of other tetracyclines, but minocycline has been associated with a high incidence of vertigo in some studies. On the other hand, minocycline appears to have little or no photosensitising potential. It is not yet clear whether minocycline can be safely used in patients with moderate or severe impairment of renal function, but if used in renal failure, the plasma urea concentration should be monitored.

Comparative susceptibility of anaerobic bacteria to minocycline, doxycycline, and tetracycline

The comparative susceptibility of 622 recent clinical isolates of anaerobic bacteria to minocycline, doxycycline, and tetracycline was determined by an agar-dilution technique. In addition to Bacteroides fragilis, a variety of other anaerobic bacteria was resistant to achievable blood concentrations of tetracycline (55% inhibited by 6.25 mug/ml) and doxycycline (58% inhibited by 2.5 mug/ml). In contrast, minocycline was significantly more active (P < 0.05) than both doxycycline and tetracycline, and 70% of strains were inhibited by achievable blood concentrations of this antibiotic (2.5 mug/ml). The enhanced activity of minocycline was particularly striking for Peptococcus asaccharolyticus, P. magnus, P. prevotii, Peptostreptococcus anaerobius, and Bacteroides melaninogenicus. Further evaluation of the clinical efficacy of minocycline against anaerobic infections is indicated.

Antimicrobial activity of 1,2,5-selenadiazoles

Ten patients with soft-tissue infections due to Staphylococcus aureus were treated with minocycline, a semisynthetic tetracycline with potent in vitro antistaphylococcal effects. Serum concentrations averaged three to five times the concentration of minocycline required to inhibit growth of S. aureus in vitro. Clearing of the infecting organism was slow (less than 50% of lesions were sterile on day 10 of therapy), but clinical improvement was noted in 8 of 10 patients.

Effect of lipoproteins on hemolytic and antifungal activity of amphotericin B and other polyene antibiotics

Tetracycline, doxycycline, and minocycline were evaluated for their antibacterial activity against methicillin-susceptible and -resistant isolates of Staphylococcus. At clinically achievable levels both doxycycline and minocycline were more active than tetracycline against methicillin-susceptible organisms. Tetracycline and doxycycline had no activity against methicillin-resistant staphylococci, whereas minocycline at 2 μg/ml inhibited six of 13 strains and, at 3 μg/ml, 10 of 13 strains.

The effect of minocycline on Candida albicans

Minocycline, a new tetracycline derivative, was found to inhibit the growth of Candida albicans. Inhibition was much affected by the composition of the medium and was difficult to demonstrate in fluid cultures. Study of the rate of budding in shallow broth cultures in Petri dishes showed that the addition of 20 mug/ml minocycline prolonged the lag phase by three hours. C. tropicalis was similarly inhibited and C. guilliermondii and C. parapsilosis to a lesser degree. Six other tetracyclines were tested and found to inhibit Candida only in very high concentrations.