Doribax: Package Insert and Label Information (Page 2 of 4)

6.2 Postmarketing Experience

The following adverse reactions have been identified during post-approval use of doripenem. Because these reactions were reported voluntarily from a population of uncertain size, it is not possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Anaphylaxis
Leukopenia
Neutropenia
Seizure
Thrombocytopenia
Toxic epidermal necrolysis, Stevens-Johnson Syndrome
Interstitial pneumonia

7 DRUG INTERACTIONS

7.1 Valproic Acid

Co-administration of DORIBAX® with valproic acid causes the serum concentrations of valproic acid to fall below the therapeutic range, increasing the risk for breakthrough seizures. Although the mechanism of this interaction is not fully understood, data from in vitro and animal studies suggest that doripenem may inhibit the hydrolysis of valproic acid’s glucuronide metabolite (VPA-g) back to valproic acid, thus decreasing the plasma concentrations of valproic acid. This is consistent with case reports for other carbapenems, where serum concentrations of valproic acid were reduced upon co-administration with a carbapenem. If administration of DORIBAX® is necessary, supplemental anti-convulsant therapy should be considered. The pharmacokinetics of doripenem were unaffected by the co-administration of valproic acid. [see Warnings and Precautions (5.3) and Clinical Pharmacology (12.3)]

7.2 Probenecid

Probenecid interferes with the active tubular secretion of doripenem, resulting in increased plasma concentrations of doripenem. [see Clinical Pharmacology (12.3)] Coadministration of probenecid with DORIBAX® is not recommended.

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Category B: Doripenem was not teratogenic and did not produce effects on ossification, developmental delays or fetal weight following intravenous administration during organogenesis at doses as high as 1 g/kg/day in rats and 50 mg/kg/day in rabbits (based on AUC, at least 2.4 and 0.8 times the exposure to humans dosed at 500 mg administered every 8 hours, respectively). There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

8.3 Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when DORIBAX® is administered to a nursing woman.

8.4 Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

8.5 Geriatric Use

Of the total number of subjects in clinical studies of DORIBAX® , 28% were 65 and over, while 12% were 75 and over. Clinical cure rates in complicated intra-abdominal and complicated urinary tract infections were slightly lower in patients ≥ 65 years of age and also in the subgroup of patients ≥ 75 years of age versus patients < 65. These results were similar between doripenem and comparator treatment groups.

This drug is known to be excreted substantially by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function or pre-renal azotemia. Because elderly patients are more likely to have decreased renal function or pre-renal azotemia, care should be taken in dose selection, and it may be useful to monitor renal function.

Elderly subjects had greater doripenem plasma concentrations relative to non-elderly subjects; however, this increase in exposure was mainly attributed to age-related changes in renal function. [see Clinical Pharmacology (12.3)]

No overall differences in safety were observed between older and younger subjects, but greater sensitivity of some older individuals cannot be ruled out.

8.6 Patients with Renal Impairment

Dosage adjustment is required in patients with moderately or severely impaired renal function. [see Dosage and Administration (2.2) and Clinical Pharmacology (12.3)] In such patients, renal function should be monitored.

10 OVERDOSAGE

In the event of overdose, DORIBAX® should be discontinued and general supportive treatment given.

Doripenem can be removed by hemodialysis. In subjects with end-stage renal disease administered DORIBAX® 500 mg, the mean total recovery of doripenem and doripenem-M1 in the dialysate following a 4-hour hemodialysis session was 259 mg (52% of the dose). However, no information is available on the use of hemodialysis to treat overdosage. [see Clinical Pharmacology (12.3)]

11 DESCRIPTION

DORIBAX® , doripenem monohydrate for injection vials contain 500 mg of doripenem on an anhydrous basis, a white to slightly-yellowish off-white sterile crystalline powder. All references to doripenem activity are expressed in terms of the active doripenem moiety. The powder is constituted for intravenous infusion. The pH of the infusion solution is between 4.5 and 5.5.

DORIBAX® is not formulated with any inactive ingredients.

DORIBAX® (doripenem monohydrate) is a synthetic broad-spectrum carbapenem antibiotic structurally related to beta-lactam antibiotics. The chemical name for doripenem monohydrate is (4R ,5S ,6S)-3-[((3S ,5S)-5-[[(aminosulfonyl)amino]methyl]-3-pyrrolidinyl)thio]-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid monohydrate.

Its molecular weight is 438.52, and its chemical structure is:

Chemical Structure
(click image for full-size original)

12 CLINICAL PHARMACOLOGY

Doripenem is a carbapenem with in vitro antibacterial activity against aerobic and anaerobic Gram-positive and Gram-negative bacteria.

12.1 Mechanism of Action

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

12.2 Pharmacodynamics

Similar to other beta-lactam antimicrobial agents, the time that unbound plasma concentration of doripenem exceeds the MIC of the infecting organism has been shown to best correlate with efficacy in animal models of infection. However, the pharmacokinetic/pharmacodynamic relationship for doripenem has not been evaluated in patients.

In a randomized, positive- and placebo-controlled crossover QT study, 60 healthy subjects were administered DORIBAX® 500 mg IV every 8 hours × 4 doses and DORIBAX® 1g IV every 8 hours × 4 doses, placebo, and a single oral dose of positive control. At both the 500 mg and 1g DORIBAX® doses, no significant effect on QTc interval was detected at peak plasma concentration or at any other time.

12.3 Pharmacokinetics

  • Plasma Concentrations

Mean plasma concentrations of doripenem following a single 1-hour intravenous infusion of a 500 mg dose of DORIBAX® to 24 healthy subjects are shown below in Figure 1. The mean (SD) plasma Cmax and AUC0–∞ values were 23.0 (6.6) µg/mL and 36.3 (8.8) µg∙hr/mL, respectively.

Figure 1. Average Doripenem Plasma Concentrations Versus Time Following a Single 1-Hour Intravenous Infusion of DORIBAX® 500 mg in Healthy Subjects (N=24)

Figure 1
(click image for full-size original)

The pharmacokinetics of doripenem (Cmax and AUC) are linear over a dose range of 500 mg to 1g when intravenously infused over 1 hour. There is no accumulation of doripenem following multiple intravenous infusions of either 500 mg or 1g administered every 8 hours for 7 to 10 days in subjects with normal renal function.

  • Distribution

The average binding of doripenem to plasma proteins is approximately 8.1% and is independent of plasma drug concentrations. The median (range) volume of distribution at steady state in healthy subjects is 16.8 L (8.09–55.5 L), similar to extracellular fluid volume (18.2 L).

Doripenem penetrates into several body fluids and tissues, including those at the site of infection for the approved indications. Doripenem concentrations in peritoneal and retroperitoneal fluid either match or exceed those required to inhibit most susceptible bacteria; however, the clinical relevance of this finding has not been established. Concentrations achieved in selected tissues and fluids following administration of DORIBAX® are shown in Table 5:

Table 5: Doripenem Concentrations in Selected Tissues and Fluids
Tissue or Fluid Dose(mg) Infusion Duration(h) Number of Samples or Subjects * Sampling Period Concentration Range (µg/mL or µg/g) Tissue- or Fluid-To-Plasma Concentration Ratio (%)Mean (Range)
*
Unless stated otherwise, only one sample was collected per subject;
Time from start of infusion;
Serial samples were collected; maximum concentrations reported;
§
Tmax range ;
BQL (Below Quantifiable Limits) in 6 subjects;
#
BQL in 1 subject;
Þ
Median (range)
Retroperitoneal fluid 250 0.5 9 30–90 min § 3.15–52.4 Range: 4.1(0.5–9.7) at 0.25 h to 990 (173–2609) at 2.5 h
500 0.5 4 90 min § 9.53–13.9 Range: 3.3 (0.0–8.1) at 0.25 h to 516 (311–842) at 6.5 h
Peritoneal exudate 250 0.5 5 30–150 min § 2.36–5.17 Range: 19.7 (0.00–47.3) at 0.5 h to 160 (32.2–322) at 4.5 h
Gallbladder 250 0.5 10 20–215 min BQL–1.87 8.02 (0.00–44.4)
Bile 250 0.5 10 20–215 min BQL–15.4# 117 (0.00–611)
Urine 500 1 110 0–4 hr 601 (BQL #–3360)Þ
500 1 110 4–8 hr 49.7 (BQL #–635)Þ
  • Metabolism

Metabolism of doripenem to a microbiologically inactive ring-opened metabolite (doripenem-M1) occurs primarily via dehydropeptidase-I. The mean (SD) plasma doripenem-M1-to-doripenem AUC ratio following single 500 mg and 1 g doses in healthy subjects is 18% (7.2%).

In pooled human liver microsomes, no in vitro metabolism of doripenem could be detected, indicating that doripenem is not a substrate for hepatic CYP450 enzymes.

  • Excretion

Doripenem is primarily eliminated unchanged by the kidneys. The mean plasma terminal elimination half-life of doripenem in healthy non-elderly adults is approximately 1 hour and mean (SD) plasma clearance is 15.9 (5.3) L/hour. Mean (SD) renal clearance is 10.8 (3.5) L/hour. The magnitude of this value, coupled with the significant decrease in the elimination of doripenem with concomitant probenecid administration, suggests that doripenem undergoes both glomerular filtration and active tubular secretion. In healthy adults given a single 500 mg dose of DORIBAX® , a mean of 71% and 15% of the dose was recovered in urine as unchanged drug and the ring-opened metabolite, respectively, within 48 hours. Following the administration of a single 500 mg dose of radiolabeled doripenem to healthy adults, less than 1% of the total radioactivity was recovered in feces after one week.

  • Special Populations

Patients with Renal Impairment

Following a single 500 mg dose of DORIBAX® , the mean AUC of doripenem in subjects with mild (CrCl 50–79 mL/min), moderate (CrCl 31–50 mL/min), and severe renal impairment (CrCl ≤30 mL/min) was 1.6-, 2.8-, and 5.1-times that of age-matched healthy subjects with normal renal function (CrCl ≥80 mL/min), respectively. Dosage adjustment is necessary in patients with moderate and severe renal impairment. [see Dosage and Administration (2.2)]

A single 500 mg dose of DORIBAX® was administered to subjects with end stage renal disease (ESRD) either one hour prior to or one hour after hemodialysis (HD). The mean doripenem AUC following the post-HD infusion was 7.8-times that of healthy subjects with normal renal function. The mean total recovery of doripenem and doripenem-M1 in the dialysate following a 4-hour HD session was 231 mg and 28 mg, respectively, or a total of 259 mg (52% of the dose). There is insufficient information to make dose adjustment recommendations in patients on hemodialysis.

Patients with Hepatic Impairment

The pharmacokinetics of doripenem in patients with hepatic impairment have not been established. As doripenem does not appear to undergo hepatic metabolism, the pharmacokinetics of doripenem are not expected to be affected by hepatic impairment.

Geriatric Patients

The impact of age on the pharmacokinetics of doripenem was evaluated in healthy male (n=6) and female (n=6) subjects ≥ 66 years of age. Mean doripenem AUC0–∞ was 49% higher in elderly adults relative to non-elderly adults. This difference in exposure was mainly attributed to age-related changes in creatinine clearance. No dosage adjustment is recommended for elderly patients with normal (for their age) renal function.

Gender

The effect of gender on the pharmacokinetics of doripenem was evaluated in healthy male (n=12) and female (n=12) subjects. Doripenem Cmax and AUC were similar between males and females. No dose adjustment is recommended based on gender.

Race

The effect of race on doripenem pharmacokinetics was examined using a population pharmacokinetic analysis of data from phase 1 and 2 studies. No significant difference in mean doripenem clearance was observed across race groups and therefore, no dosage adjustment is recommended based on race.

  • Drug Interactions

Administration of DORIBAX® 500 mg every 8 hours × 4 doses to 23 healthy male subjects receiving valproic acid 500 mg every 12 hours for 7 days decreased the mean Cmax of valproic acid by 44.5% (from 86.1 mcg/mL to 47.8 mcg/mL) and the mean Cmin by 77.7% (from 55.7 mcg/mL to 12.4 mcg/mL) compared to administration of valproic acid alone. The mean AUC0–tau of valproic acid also decreased by 63%. Conversely, the Cmax of the VPA-g metabolite was increased by 62.6% (from 5.19 mcg/mL to 8.44 mcg/mL) and the mean AUC0–tau of VPA-g was increased by 50%. The pharmacokinetics of doripenem were unaffected by the co-administration of valproic acid. [see Warnings and Precautions (5.2) and Drug Interactions (7.1)]

Probenecid interferes with the active tubular secretion of doripenem, resulting in increased plasma concentrations. Probenecid increased doripenem AUC by 75% and prolonged the plasma elimination half-life by 53%. [see also Drug Interactions (7.2)]

In vitro studies in human liver microsomes and hepatocytes indicate that doripenem does not inhibit the major cytochrome P450 isoenzymes (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4/5, and CYP4A11). Therefore, DORIBAX® is not expected to inhibit the clearance of drugs that are metabolized by these metabolic pathways in a clinically relevant manner.

DORIBAX® is also not expected to have CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A4/5, or UGT1A1 enzyme-inducing properties based on in vitro studies in cultured human hepatocytes.

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