Objective  To evaluate the efficacy of intravenous doxycycline as empirical treatment in hospitalized patients with mild to moderately severe community-acquired pneumonia.

Patients and Methods  We conducted a randomized prospective trial to compare the efficacy of intravenous doxycycline with other routinely used antibiotic regimens in 87 patients admitted with the diagnosis of community-acquired pneumonia. Forty-three patients were randomized to receive 100 mg of doxycycline intravenously every 12 hours while 44 patients received other antibiotic(s) (control group). The 2 patient groups were comparable in their clinical and laboratory profiles.

Results  The mean ± SD interval between starting an antibiotic and the clinical response was 2.21 ± 2.61 days in the doxycycline group compared with 3.84 ± 6.39 days in the control group (P = .001). The mean ± SD length of hospitalization was 4.14 ± 3.08 days in the doxycycline group compared with 6.14 ± 6.65 days in the control group (P = .04). The median cost of hospitalization was $5126 in the doxycycline group compared with $6528 in the control group (P = .04). The median cost of antibiotic therapy in the doxycycline-treated patients ($33) was significantly lower than in the control group ($170.90) (P<.001). Doxycycline was as efficacious as the other regimens chosen for the treatment of community-acquired pneumonia.

Conclusion  Doxycycline is an effective and inexpensive therapy for the empirical treatment of hospitalized patients with mild to moderately severe community-acquired pneumonia.

In patients hospitalized with the diagnosis of community-acquired pneumonia (CAP), antibiotics are usually chosen empirically to treat the most likely causative organisms until a microbiologic cause is established. However, a definitive cause is not usually established; and if there is a good clinical response, the course of therapy is completed with the initially chosen antibiotic. Combinations of antibiotics are often used and these regimens can be expensive.

Considerations in choosing antibiotics should include the following: antibacterial spectrum, efficacy, adverse effects, ease of administration, and cost.

In various studies from the literature, percentage of cases where no definitive cause for CAP was established ranged from 32.9%³ to 63.3%.⁴ The most commonly detected organism was Streptococcus pneumoniae, ranging from 8.5%⁵ to 37.6%.⁴ Atypical pneumonias caused by Legionella, Chlamydia, and Mycoplasma together accounted for 8% to 20% of the cases.^3-6

Doxycycline has a high degree of activity against many common respiratory pathogens including S pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, anaerobes such as Bacteroides and anaerobic/microaerophilic streptococci and atypical agents like Legionella, Mycoplasma pneumoniae, and Chlamydia pneumoniae.⁷ Doxycycline has been used as oral therapy in the outpatient management of lower respiratory tract infections (including pneumonia), where it has been compared with ofloxacin and spiramycin, and has been found to be comparable.^8-10 Doxycycline is an attractive alternative for hospitalized patients with mild to moderately severe CAP. The objective of this study was to evaluate the efficacy of intravenous doxycycline as empirical treatment in hospitalized patients with mild to moderately severe CAP.

PATIENTS, MATERIALS, AND METHODS

During the study period there were a total of 356 patients admitted with the diagnosis of pneumonia. Of these 356 patients, 136 were from long-term care facilities. Forty-six patients required intubation in the emergency department. Thirty-eight had 1 of the exclusion criteria including immunocompromised state, renal or hepatic failure, or pregnancy. Another 22 patients received antibiotics before enrollment. In 27 patients who were not enrolled in the study, consent could not be obtained. Eighty-seven patients hospitalized with CAP were randomly assigned to receive either doxycycline or 1 or more antibiotics selected by the patient's physician.

The randomization process was done by a predetermined numbered sequence. As the patients were enrolled into the study, they were assigned to either the doxycycline group or the control group depending on the number to which they were assigned.

The Institutional Research and Review Committee of the hospital approved the study protocol. All patients were informed about the study and a written consent was obtained.

PATIENTS

After enrollment, patients were interviewed and information was recorded on a standard data collection form. Data included demographic information, history, physical examination, and admission laboratory findings. All patients had baseline investigations that included a chest radiograph, complete blood cell count with differential, serum electrolytes, serum urea nitrogen, serum glucose, pulse oximetry or arterial blood gases, sputum Gram stain and culture, and blood cultures. All patients were examined daily for their complete blood cell counts and electrolyte levels. Additional tests such as sputum, acid-fast stains, serology for Chlamydia, Mycoplasma, and Legionella were performed when clinically indicated, at the discretion of the patient's physician.

COMORBID CONDITIONS

Conditions such as chronic obstructive pulmonary disease, coronary artery disease, congestive heart failure, neoplastic disease, diabetes mellitus, chronic renal failure, alcoholism, and smoking were recorded.

TREATMENT

Doxycycline (100 mg) was given intravenously every 12 hours in patients randomized to the study group. In patients randomized to the control group, the physician taking care of the patient chose antibiotics without restrictions. All patients were monitored daily by one of us for improvement or deterioration while receiving therapy and were also monitored for any adverse drug effects.

CRITERIA FOR RESPONSE

The time to respond to treatment was defined as the number of days between the day of randomization (day 1) and the day on which the last of the following parameters was met: (1) oral temperature of 37.9°C or lower over 3 consecutive 8-hour periods; (2) beginning of a decrease in total white blood cell counts, ie, the day the count showed a tendency toward normal in patients who had leukocytosis; (3) subjective improvement of symptoms for which the patient was admitted to the hospital. This was decided by the primary physician's clinical notes and interview of the patient by one of us; and (4) in patients with no underlying disease like chronic obstructive pulmonary disease, congestive heart failure, and who were hypoxic on admission, resolution of hypoxia.

Patients who showed any sign of deterioration or who were not responding to therapy or who developed serious adverse effects had their antibiotic regimen changed at the discretion of the physician taking care of them. Patients who improved while receiving therapy were switched to an oral regimen, which in the study group was 100 mg of doxycycline orally every 12 hours. The attending physician determined the time of discharge.

STUDY CRITERIA

The 2 patient groups were then compared on the following parameters: (1) time to resolution of morbidity, (2) length of hospital stay, (3) cost of antibiotics during hospitalization, (4) cost of hospitalization, (5) adverse effects from the use of antibiotics, and (6) number of antibiotics used per patient, including the antibiotic on discharge. The time to respond to treatment was calculated as described earlier. The length of hospital stay was calculated by subtracting the admission date from the discharge date. The cost of antibiotics used during hospitalization was obtained from the number of antibiotic doses times the cost of each dose. The cost of each dose of antibiotic was obtained from the miniformulary of the pharmacy department of the hospital and was the amount charged to the patient. The mean cost of antibiotic in the doxycycline and the control groups included the antibiotics that were used even when the patient failed while receiving initial therapy. The cost of hospitalization was obtained from the computer records of the hospital bill and not the actual payment made.

STATISTICAL ANALYSIS

Comparison of patient age was done by Student 2-sample t test. All other variables were analyzed by Wilcoxon rank sum test rather than the Student t test, because of violation of the distributional normality assumption. Because of nonnormal distributions exhibited by most of these variables, medians along with the means and SDs were calculated. The adverse effects were compared by the ² test. P<.05 was considered to indicate statistical significance.

RESULTS

View this table: [in this window] [in a new window] Table 1. Clinical Features Comparing the Doxycycline-Treated Patients and Control Patients

View this table: [in this window] [in a new window] Table 2. Laboratory Features Comparing the Doxycycline and Control Groups*

The ages of the patients in the doxycycline and control groups ranged from 18 to 84 years, and 23 to 81 years, respectively ( Table 1). However, only 20 (23%) of the 87 patients were older than 60 years. Twenty-seven patients (63%) in the doxycycline group and 21 (48%) in the control group were women. The average number of comorbid conditions between the 2 groups were not statistically significant (P = .18). In both groups, 40% of the patients had documented underlying lung disease.

The median cost of antibiotic(s) during hospitalization for the doxycycline group was $33, compared with $170.9 in the control group (P<.001) (Table 3). The median cost of hospitalization in the doxycycline group was $5126, compared with $6528 in the control group (P = .04) ( Table 3). The mean ± SD time to respond to treatment was 2.21 ± 2.61 days in the doxycycline group, compared with 3.84 ± 6.39 days in the control group (P = .001) ( Table 3). The mean ± SD length of hospitalization was 4.14 ± 3.08 days in the doxycycline group, compared with 6.14 ± 6.65 days in the control group (P = .04) ( Table 3). The mean ± SD number of antibiotics used, including the one given on discharge, was significantly lower in the doxycycline group than in the control group: 1.16 ± 1.04 in the doxycycline group vs 2.43 ± 1.59 in the control group (P<.001) ( Table 3).

View this table: [in this window] [in a new window] Table 3. Response to Treatment: Comparison Between the Doxycycline-Treated Patients and Control Patients*

In the doxycycline group, 6 patients developed adverse effects, but none required a change of antibiotic because of the adverse effects. In the control group, 11 patients had adverse effects (P = .19) and 3 of these 11 required a change of antibiotic. Two patients had diarrhea with the use of clindamycin and 1 patient had severe vomiting with the use of erythromycin; hence, their antibiotics were changed.

Three patients in the doxycycline group required a change in antibiotic because of a lack of response. Two patients failed to respond to the use of doxycycline. One patient was misdiagnosed and had tuberculosis on the basis of a strongly positive tuberculin skin test and a persistent infiltrate on chest radiograph. This was not confirmed by cultures; however, the patient improved with antituberculous treatment.

Eight patients in the control group required a change in the antibiotic regimen, 3 because of adverse effect (as described earlier) and 5 because of a lack of response.

Of the 87 patients enrolled in the study, 7 were found to have pneumococcal bacteremia. Three of these 7 patients received doxycycline and 4 received other antibiotics. The pneumococci were sensitive to the use of penicillin in 6 of the 7 patients. One patient had intermediate-level resistance to penicillin and he had been randomized to the control group. All these isolates were susceptible to the use of tetracycline. All 7 patients recovered and were discharged from the hospital.

From January to June 1997 in our hospital system, 10% of S pneumoniae isolates had high-level resistance to penicillin (minimal inhibitory concentration, 2 µg/mL) and another 10% had intermediate-level resistance to penicillin (minimal inhibitory concentration, 0.1-1.0 µg/mL). Resistance to tetracycline was 6.5%. Of the penicillin-resistant pneumococci, 16.6% were resistant to tetracycline (B.N.M., written communication, May 18, 1998).

COMMENT

The empirical treatment of CAP has many options. Some of the options involve the use of 2 agents to cover the common respiratory pathogens like S pneumoniae, H influenzae, as well as organisms that cause atypical pneumonia. According to the recommendations of the Infectious Diseases Society of America,¹² the empirical treatment for patients hospitalized to the general wards includes a -lactam antibiotic with or without a macrolide or a quinolone.¹² Doxycycline has been recommended only in the empirical treatment of outpatients with CAP.¹² Even in the recommendations of the American Thoracic Society,¹³ tetracycline has been recommended only as an outpatient treatment of CAP.

Historically, tetracycline is considered inferior to penicillin in the treatment of S pneumoniae infections. However, in certain places there has been a changing trend, with decreasing tetracycline resistance and increasing penicillin resistance.¹⁴ In the United States, 7.5% of S pneumoniae are resistant to tetracycline.¹⁵ Moreover, tetracycline resistance is not the same as doxycycline resistance. In a study of 256 clinical isolates of S pneumoniae described by Shea and Cunha,⁷ 30% were resistant to penicillin, 20% to tetracycline, and only 5% to doxycycline. Plouffe et al¹⁶ reported antimicrobial susceptibilities on 499 isolates of S pneumoniae from Franklin County, Ohio, between 1991 and 1994. Doxycycline was found to have excellent activity against pneumococcus (99.2% isolates susceptible) with no trend toward decreasing susceptibilities. High-level penicillin resistance was found in 5 isolates, and all of them were susceptible to doxycycline. Among isolates with intermediate level of sensitivity to penicillin, only 6% were not susceptible to doxycycline.¹⁶

Our study shows doxycycline to be effective for the empirical treatment of hospitalized patients with mild to moderately severe CAP.

Some limitations of this study include (1) the study was not blinded, (2) patients with severe disease requiring intubation were excluded, (3) the cause of pneumonia was not established in most of our patients, and (4) we did not perform antibacterial susceptibilities of the organisms isolated against doxycycline.

Doxycycline has activity against the common respiratory pathogens, relatively low toxicity, very low cost, and a convenient twice-daily dosing. It should be considered in the empirical treatment of hospitalized patients with mild to moderately severe CAP.

Presented in part as an oral research abstract at the annual meeting of the American College of Physicians, Ohio chapter, Columbus, August 15, 1997.

We thank Burton C. West, MD, for his contribution in this study and help in preparing the manuscript; Adrian Caracioni, Marketa Kasalova, Ali Malick, and Jan Kasal for their contribution in enrolling patients during this study; and Gordon Jacobsen, statistician at the Henry Ford Health System, Detroit, Mich, for help with the statistical analysis.

Reprints: Raja Shekar, MD, Department of Medicine, Meridia Huron Hospital, 13951 Terrace Rd, East Cleveland, OH 44112.