Doxycycline Hyclate (Page 4 of 6)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Doxycycline is an antibacterial drug [see Microbiology (12.4) ].

12.3 Pharmacokinetics

Following single and multiple-dose administration of doxycycline hyclate delayed-release tablets, 200 mg to adult volunteers, average peak plasma doxycycline concentration (Cmax ) was 4.6 mcg/mL and 6.3 mcg/mL, respectively with median tmax of 3 hours; the corresponding mean plasma concentration values 24 hours after single and multiple doses were 1.5 mcg/mL and 2.3 mcg/mL, respectively.

Absorption

Doxycycline is virtually completely absorbed after oral administration.

Effect of Food

The mean Cmax and AUC 0-∞ of doxycycline are 24% and 13% lower, respectively, following single dose administration of doxycycline hyclate delayed-release tablets, 100 mg with a high fat meal (including milk) compared to fasted conditions. The mean Cmax of doxycycline is 19% lower and the AUC 0-∞ is unchanged following single dose administration of doxycycline hyclate delayed-release tablets, 150 mg with a high fat meal (including milk) compared to fasted conditions. The clinical significance of these decreases is unknown. Doxycycline bioavailability from doxycycline hyclate delayed-release tablets, 200 mg was not affected by food, but the incidence of nausea was higher in fasted subjects. The 200 mg tablets may be administered without regard to meals.

When doxycycline hyclate delayed-release tablets are sprinkled over applesauce and taken with or without water, the extent of doxycycline absorption is unchanged, but the rate of absorption is increased slightly.

Elimination

Tetracyclines are concentrated in bile by the liver and excreted in the urine and feces at high concentrations and in a biologically active form. Excretion of doxycycline by the kidney is about 40%/72 hours in individuals with a creatinine clearance of about 75 mL/min. This percentage may fall as low as 1-5%/72 hours in individuals with a creatinine clearance below 10 mL/min.

Specific Populations

Patients with Renal Impairment

Studies have shown no significant difference in the serum half-life of doxycycline (range 18 to 22 hours) in individuals with normal and severely impaired renal function. Hemodialysis does not alter the serum half-life.

Pediatric Patients

Population pharmacokinetic analysis of sparse concentration-time data of doxycycline. Following standard of care intravenous and oral dosing in 44 children (2-18 years of age) showed that allometrically-scaled clearance of doxycycline in children ≥2 to ≤8 years of age (median [range] 3.58 [2.27-10.82] L/h/70 kg, N=11) did not differ significantly from children >8 to 18 years of age (3.27 [1.11-8.12] L/h/70 kg, N=33). For pediatric patients weighing ≤45 kg, body weight normalized doxycycline CL in those ≥2 to ≤8 years of age (median [range] 0.071 [0.041-0.202] L/kg/h, N=l0) did not differ significantly from those >8 to 18 years of age (0.081 [0.035-0.126] L/kg/h, N=8). In pediatric patients weighing >45 kg no clinically significant differences in body weight normalized doxycycline CL were observed between those ≥2 to ≤8 years (0.050 L/kg/h, N=l) and those >8 years of age (0.044 [0.014-0.121] L/kg/h, N=25). No clinically significant difference in CL differences between oral and IV were observed in the small cohort of pediatric patients who received the oral (N=l9) or IV (N=21) formulation alone.

12.4 Microbiology

Mechanism of Action

Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. Doxycycline has bacteriostatic activity against a broad range of Gram-positive and Gram-negative bacteria.

Resistance

Cross-resistance between tetracyclines is common.

Antimicrobial Activity

Doxycycline has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections. [see Indications and Usage (1) ].

Gram-Negative Bacteria

Acinetobacter species
Bartonella bacilliformis
Brucella species
Campylobacter fetus
Enterobacter aerogenes
Escherichia coli
Francisella tularensis
Haemophilus ducreyi
Haemophilus influenzae
Klebsiella granulomatis
Klebsiella species
Neisseria gonorrhoeae
Shigella species
Vibrio cholerae
Yersinia pestis

Gram-Positive Bacteria

Bacillus anthracis
Listeria monocytogenes
Streptococcus pneumoniae

Anaerobic Bacteria

Clostridium species
Fusobacterium fusiforme
Propionibacterium acnes

Other Bacteria

Norcardiae and other aerobic Actinomyces species
Borrelia recurrentis
Chlamydophila psittaci
Chlamydia trachomatis
Mycoplasma pneumoniae
Rickettsiae
Treponema pallidum
Treponema pallidum subspecies pertenue
Ureaplasma urealyticum

Parasites

Balantidium coli
Entamoeba speciesPlasmodium falciparum 1


1
Doxycycline has been found to be active against the asexual erythrocytic forms of Plasmodium falciparum but not against the gametocytes of P. falciparum. The precise mechanism of action of the drug is not known.

Susceptibility Testing

For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals to evaluate carcinogenic potential of doxycycline have not been conducted. However, there has been evidence of oncogenic activity in rats in studies with the related antibacterials, oxytetracycline (adrenal and pituitary tumors) and minocycline (thyroid tumors). Likewise, although mutagenicity studies of doxycycline have not been conducted, positive results in in vitro mammalian cell assays have been reported for related antibacterials (tetracycline, oxytetracycline).

Doxycycline administered orally at dosage levels as high as 250 mg/kg/day had no apparent effect on the fertility of female rats. Effect on male fertility has not been studied.

13.2 Animal Toxicology and/or Pharmacology

Hyperpigmentation of the thyroid has been produced by members of the tetracycline- class in the following species: in rats by oxytetracycline, doxycycline, tetracycline PO4 , and methacycline; in minipigs by doxycycline, minocycline, tetracycline PO4 , and methacycline; in dogs by doxycycline and minocycline; in monkeys by minocycline.

Minocycline, tetracycline PO4 , methacycline, doxycycline, tetracycline base, oxytetracycline HCl, and tetracycline HCl, were goitrogenic in rats fed a low iodine diet. This goitrogenic effect was accompanied by high radioactive iodine uptake. Administration of minocycline also produced a large goiter with high radioiodine uptake in rats fed a relatively high iodine diet.

Treatment of various animal species with this class of drugs has also resulted in the induction of thyroid hyperplasia in the following: in rats and dogs (minocycline); in chickens (chlortetracycline); and in rats and mice (oxytetracycline). Adrenal gland hyperplasia has been observed in goats and rats treated with oxytetracycline.

Results of animal studies indicate that tetracyclines cross the placenta and are found in fetal tissues.

14 CLINICAL STUDIES

This was a randomized, double-blind, active-controlled, multicenter trial which enrolled 495 subjects, between 19 to 45 years of age with a confirmed diagnosis of urogenital C. trachomatis infection less than 14 days prior to enrollment, or partner(s) of a subject with a known positive test for urogenital C. trachomatis infection.

The primary purpose of this study was to evaluate the efficacy and safety of doxycycline hyclate delayed-release tablets Tablets, 200 mg once daily versus doxycycline hyclate capsules, 100 mg twice daily for seven days for the treatment of uncomplicated urogenital C. trachomatis infection. The primary efficacy objective was to demonstrate non-inferiority of the doxycycline hyclate delayed-release tablets, 200 mg once daily treatment regimen versus the doxycycline 100 mg twice daily treatment regimen for the indication using a negative nucleic acid amplification test (NAAT) at the test of cure visit (day 28) in the mITT population (subjects who were positive at baseline and took at least one day of study drug).

Table 2: Primary Efficacy Outcome – Microbiological Cure of C. trachomatis at Day 28
mITT Population Doxycycline hyclate delayed-release tablets, 200 mg once dailyCure Rate (%) Doxycycline hyclate capsules, 100 mg twice dailyCure Rate (%) Difference(%)
N 188 190
Microbiological Cure, n (%) 163 (86.7) 171 (90.0) -3.3%
95% Confidence Interval for Cure Rate -10.3, 3.7

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