Doribax

Overdose

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 doripenemM1 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.

Contraindications

DORIBAX® is contraindicated in patients with known serious hypersensitivity to doripenem or to other drugs in the same class or in patients who have demonstrated anaphylactic reactions to beta-lactams.

Undesirable effects

The following adverse reactions are discussed in greater detail in other sections of labeling:

• Anaphylaxis and serious hypersensitivity reactions
• Seizures
• Interaction with sodium valproate
• Clostridium difficile-associated diarrhea
• Development of drug-resistant bacteria
• Pneumonitis with inhalational use

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in clinical trials of a drug cannot be compared directly to rates from clinical trials of another drug and may not reflect rates observed in practice.

During clinical investigations, 1338 adult patients were treated with DORIBAX® (1076 patients received doripenem 500 mg administered over 1 hour every 8 hours and 262 patients received doripenem 500 mg administered over 4 hours every 8 hours); in some patients parenteral therapy was followed by a switch to an oral antimicrobial.. The median age of patients treated with DORIBAX® was 54 years (range 18– 90) in the comparative complicated urinary tract infections (cUTI) study, 46 years (range 18–94) in the pooled comparative complicated intra-abdominal infections (cIAI) studies, and 56 years (range 18-94) in the other Phase 3 trials. There was a female predominance (62%) in the comparative cUTI study and a male predominance (63% and 75%) in the comparative cIAI and other Phase 3 trials, respectively. The patients treated with DORIBAX® were predominantly Caucasian (79%) in the five comparator-controlled Phase 3 studies.

The most common adverse drug reactions ( ≥ 5%) observed in the five DORIBAX® comparator-controlled Phase 3 clinical trials were anemia, headache, nausea, diarrhea, rash, phlebitis, and elevated hepatic enzymes. During clinical trials, adverse events led to discontinuation of DORIBAX® in 4.1% (55 of 1338) of patients compared to 4.3% (58 of 1325) of comparator-treated patients.

Adverse reactions due to DORIBAX® 500 mg every 8 hours that occurred at a rate ≥ 1 % are listed in Table 4. Hypersensitivity reactions related to intravenous study drug occurred at a rate of less than 1%.

Table 4: Adverse Reactions with Incidence Rates (%) of ≥ 1% in the Controlled Phase 3 Clinical Trials

In a Phase 1 study of healthy subjects receiving doripenem doses greater than the approved dose of 500 mg every 8 hours for 10 to 14 days, the incidence of rash was higher than that observed in subjects who received 500 mg every 8 hours. The rash resolved within 10 days after doripenem administration was discontinued.

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.

Hematologic: Leukopenia, Neutropenia, Thrombocytopenia

Immune System: Anaphylaxis

Nervous System: Seizure

Renal: Renal impairment/failure

Respiratory: Interstitial pneumonia

Skin: Toxic epidermal necrolysis, Stevens-Johnson Syndrome

Therapeutic indications

DORIBAX® (doripenem for injection) is indicated as a single agent for the treatment of complicated intra-abdominal infections caused by Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Bacteroides caccae, Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides uniformis, Bacteroides vulgatus, Streptococcus intermedius, Streptococcus constellatus and Peptostreptococcus micros.

DORIBAX® (doripenem for injection) is indicated as a single agent for the treatment of complicated urinary tract infections, including pyelonephritis caused by Escherichia coli including cases with concurrent bacteremia, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, and Acinetobacter baumannii.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of DORIBAX® and other antibacterial drugs, DORIBAX® should be used only to treat infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting and modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

Pharmacodynamic properties

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® 1 g IV every 8 hours × 4 doses, placebo, and a single oral dose of positive control. At both the 500 mg and 1 g DORIBAX® doses, no significant effect on QTc interval was detected at peak plasma concentration or at any other time.

Pharmacokinetic properties

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)

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

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

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.

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 10.3 (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.

Fertility, pregnancy and lactation

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.

Special warnings and precautions for use

Included as part of the PRECAUTIONS section.

In a clinical trial of patients with ventilator-associated bacterial pneumonia comparing doripenem to imipenem, more subjects receiving doripenem died 23% (31/135) compared to those receiving imipenem 16.7% (22/132) based on 28-day all-cause mortality in the intent-to-treat (ITT) population. Clinical response rates were also lower in the doripenem arm. Doripenem is not approved for the treatment of ventilator-associated bacterial pneumonia.

Serious and occasionally fatal hypersensitivity (anaphylactic) and serious skin reactions have been reported in patients receiving beta-lactam antibiotics. These reactions are more likely to occur in individuals with a history of sensitivity to multiple allergens. Before therapy with DORIBAX® is instituted, careful inquiry should be made to determine whether the patient has had a previous hypersensitivity reaction to other carbapenems, cephalosporins, penicillins or other allergens. If this product is to be given to a penicillin-or other beta-lactam-allergic patient, caution should be exercised because cross-reactivity among beta-lactam antibiotics has been clearly documented.

If an allergic reaction to DORIBAX® occurs, discontinue the drug. Serious acute hypersensitivity (anaphylactic) reactions require emergency treatment, as clinically indicated.

Seizures have been reported during treatment with doripenem (see Postmarketing Experience). In clinical trials, doripenem-treated patients with pre-existing central nervous system (CNS) disorders (e.g. stroke or history of seizures), patients with compromised renal function and patients given doses greater than 500 mg every 8 hours appear to be at greater risk for developing seizures.

Due to a drug interaction, patients with seizure disorders controlled with valproic acid or sodium valproate will be at an increased risk for breakthrough seizures when treated with DORIBAX® concomitantly. Reduction in serum valproic acid concentrations to below the therapeutic concentration range (50 to 100 mcg/mL) was observed by 12 hours after the initiation of doripenem in healthy subjects co-administered both drugs. A similar drug interaction involving other carbapenem antibacterials and valproic acid has been described in published case reports. In some of these reports, increasing the dose of valproic acid or sodium valproate did not result in increased valproic acid serum concentrations. Alternative antibacterial therapies should be considered for patients receiving valproic acid or sodium valproate. If administration of DORIBAX® is necessary, supplemental anti-convulsant therapy should be considered.

Clostridium difficile-associated diarrhea (CDAD) has been reported with nearly all antibacterial agents and may range in severity from mild diarrhea to fatal colitis.

Treatment with antibacterial agents alters the normal flora of the colon and may permit overgrowth of C. difficile.

C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.

If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.

Prescribing DORIBAX® in the absence of a proven or strongly suspected bacterial infection is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

When DORIBAX® has been used investigationally via inhalation, pneumonitis has occurred. DORIBAX® should not be administered by this route.

Because of the short duration of treatment and intermittent clinical use, long-term carcinogenicity studies have not been conducted with doripenem.

Doripenem did not show evidence of mutagenic activity in standard tests that included bacterial reverse mutation assay, chromosomal aberration assay with Chinese hamster lung fibroblast cells, and mouse bone marrow micronucleus assay.

Intravenous injection of doripenem had no adverse effects on general fertility of treated male and female rats or on postnatal development and reproductive performance of the offspring at doses as high as 1 g/kg/day (based on AUC, greater than 1.5 times the exposure to humans at the dose of 500 mg administered every 8 hours).

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.

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.

Safety and effectiveness in pediatric patients have not been established.

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.

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

Dosage adjustment is required in patients with moderately or severely impaired renal function. In such patients, renal function should be monitored.

Dosage (Posology) and method of administration

The recommended dosage of DORIBAX® is 500 mg administered every 8 hours by intravenous infusion over one hour in patients ≥ 18 years of age. The recommended dosage and administration by infection is described in Table 1:

Table 1: Dosage of DORIBAX ® by Infection

Table 2: Dosage of DORIBAX®  in Patients with Renal Impairment

The following formula may be used to estimate CrCl. The serum creatinine used in the formula should represent a steady state of renal function.

DORIBAX® is hemodialyzable; however, there is insufficient information to make dose adjustment recommendations in patients on hemodialysis.

DORIBAX® does not contain a bacteriostatic preservative. Aseptic technique must be followed in preparation of the infusion solution.

To prepare DORIBAX® infusions in Baxter Minibag Plus™ infusion bags consult the infusion bag manufacturer's instructions.

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to use whenever solution and container permit. DORIBAX® infusions range from clear, colorless solutions to solutions that are clear and slightly yellow. Variations in color within this range do not affect the potency of the product.

• Constitute the 500 mg vial with 10 mL of sterile water for injection or 0.9% sodium chloride injection (normal saline) and gently shake to form a suspension. The resultant concentration is approximately 50 mg/mL. CAUTION: THE CONSTITUTED SUSPENSION IS NOT FOR DIRECT INJECTION.
• Withdraw the suspension using a syringe with a 21 gauge needle and add it to an infusion bag containing 100 mL of normal saline or 5% dextrose; gently shake until clear. The final infusion solution concentration is approximately 4.5 mg/mL.

• Constitute the 250 mg vial with 10 mL of sterile water for injection or 0.9% sodium chloride injection (normal saline) and gently shake to form a suspension. The resultant concentration is approximately 25 mg/mL. CAUTION: THE CONSTITUTED SUSPENSION IS NOT FOR DIRECT INJECTION.
• Withdraw the suspension using a syringe with a 21 gauge needle and add it to an infusion bag containing either 50 or 100 mL of normal saline or 5% dextrose; gently shake until clear. The final infusion solution concentration is approximately 4.2 mg/mL (50 mL infusion bag) or approximately 2.3 mg/mL (100 mL infusion bag).

• Constitute the 500 mg vial with 10 mL of sterile water for injection or 0.9% sodium chloride injection (normal saline) and gently shake to form a suspension. The resultant concentration is approximately 50 mg/mL. CAUTION: THE CONSTITUTED SUSPENSION IS NOT FOR DIRECT INJECTION.
• Withdraw the suspension using a syringe with a 21 gauge needle and add it to an infusion bag containing 100 mL of normal saline or 5% dextrose; gently shake until clear.
• Remove 55 mL of this solution from the bag and discard.
• Infuse the remaining solution, which contains 250 mg (approximately 4.5 mg/mL).

The compatibility of DORIBAX® with other drugs has not been established. DORIBAX® should not be mixed with or physically added to solutions containing other drugs.

Upon constitution with sterile water for injection or 0.9% sodium chloride (normal saline) injection, DORIBAX® suspension in the vial may be held for 1-hour prior to transfer and dilution in the infusion bag.

Following dilution of the suspension with normal saline or 5% dextrose, DORIBAX® infusions stored at room temperature or under refrigeration should be completed according to the times in Table 3.

Table 3: Storage and Stability Times of Infusion Solutions Prepared in Normal Saline or 5% Dextrose

Constituted DORIBAX® suspension or DORIBAX® infusion should not be frozen. This storage information applies also to DORIBAX® diluted in Baxter Minibag Plus™.

Interaction with other medicinal products and other forms of interaction

Administration of DORIBAX® 500 mg every 8 hours x 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.

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%.

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.