DOXYCYCLINE- doxycycline capsule
Doxycycline is a broad-spectrum antibacterial synthetically derived from oxytetracycline. Doxycycline capsules USP, 75 mg, and 100 mg contain doxycycline monohydrate equivalent to 75 mg, and 100 mg of doxycycline for oral administration. The chemical designation of the light yellow to pale yellow powder is 2-Naphthacenecarboxamide, 4-(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-,[4 S -(4a,4a∝,5∝,5a∝,6∝,12a∝,)]-, monohydrate.
C 22 H 24 N 2 O 8 • H 2 O M.W. = 462.45
Doxycycline has a high degree of lipid solubility and a low affinity for calcium binding. It is highly stable in normal human serum. Doxycycline will not degrade into an epianhydro form.
Inert ingredients: colloidal silicon dioxide; magnesium stearate; microcrystalline cellulose; sodium starch glycolate; and a hard gelatin capsule which contains iron oxide black, iron oxide red, iron oxide yellow, titanium dioxide, gelatin, sodium lauryl sulfate for the 75 mg strength and iron oxide black, iron oxide red, iron oxide yellow, titanium dioxide, FD & C Red # 3, D&C Yellow # 10, gelatin, sodium lauryl sulfate for the 100 mg strength. The capsules are printed with edible ink containing shellac, titanium dioxide, black iron oxide, brown iron oxide and potassium hydroxide for 75 mg and 100 mg strengths.
Tetracyclines are readily absorbed and are bound to plasma proteins in varying degrees. They are concentrated by the liver in the bile and excreted in the urine and feces at high concentrations in a biologically active form. Doxycycline is virtually completely absorbed after oral administration.
Following a 200 mg dose of doxycycline monohydrate, 24 normal adult volunteers averaged the following serum concentration values:
|Average Observed Values|
|Maximum Concentration||3.61 mcg/mL (± 0.9 sd)|
|Time of Maximum Concentration||2.60 hr (± 1.10 sd)|
|Elimination Rate Constant||0.049 per hr (± 0.030 sd)|
|Half-Life||16.33 hr (± 4.53 sd)|
Excretion of doxycycline by the kidney is about 40%/72 hours in individuals with normal function (creatinine clearance about 75 mL/min). This percentage excretion may fall as low as 1-5%/72 hours in individuals with severe renal insufficiency (creatinine clearance below 10 mL/min). Studies have shown no significant difference in serum half-life of doxycycline (range 18 to 22 hours) in individuals with normal and severely impaired renal function.
Hemodialysis does not alter serum half-life.
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.
Cross resistance with other tetracyclines is common.
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).
Nocardiae and other Actinomyces species
Treponema pallidum subspecies pertenue
Balantidium coli Entamoeba species
When available, the clinical microbiology laboratory should provide cumulative reports of in vitro susceptibility test results for antimicrobial drugs used in local hospitals and practice areas as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting the most effective antimicrobial.
Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized test method (broth and /or agar). 1,2,4,6,7 The MIC values should be interpreted according to criteria provided in Table 1.
Quantitative methods that require measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using a standardized test method. 1,3,4 This procedure uses paper disks impregnated with 30 mcg doxycycline to test the susceptibility of microorganisms to doxycycline. The disk diffusion interpretive criteria are provided in Table 1.
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