Baclofen

DRUG INTERACTIONS There is inadequate systematic experience with the use of baclofen injection (intrathecal) in combination with other medications to predict specific drug-drug interactions. Interactions attributed to the combined use of baclofen injection (intrathecal) and epidural morphine include hypotension and dyspnea.

Indicated for "the alleviation of signs and symptoms of spasticity resulting from multiple sclerosis, particularly for the relief of flexor spasms and concomitant pain, clonus, and muscular rigidity," and in patients with spinal cord injuries or disease. The label notes it is "not indicated in the treatment of skeletal muscle spasm resulting from rheumatic disorders" and has not been shown effective for spasticity due to stroke, cerebral palsy, or Parkinson's disease.

DOSAGE AND ADMINISTRATION Refer to the manufacturer's manual for the implantable pump approved for intrathecal infusion for specific instructions and precautions for programming the pump and/or refilling the reservoir. There are various pumps with varying reservoir volumes and there are various refill kits available. It is important to be familiar with all of these products in order to select the appropriate refill kit for the particular pump in use. Screening Phase: Prior to pump implantation and initiation of chronic infusion of baclofen injection (intrathecal), patients must demonstrate a positive clinical response to a baclofen injection (intrathecal) bolus dose administered intrathecally in a screening trial. The screening trial employs baclofen injection (intrathecal) at a concentration of 50 mcg per mL. A 1 mL ampule (50 mcg per mL) is available for use in the screening trial. The screening procedure is as follows. An initial bolus containing 50 micrograms in a volume of 1 milliliter is administered into the intrathecal space by barbotage over a period of not less than one minute. The patient is observed over the ensuing 4 to 8 hours. A positive response consists of a significant decrease in muscle tone and/or frequency and/or severity of spasms. If the initial response is less than desired, a second bolus injection may be administered 24 hours after the first. The second screening bolus dose consists of 75 micrograms in 1.5 milliliters. Again, the patient should be observed for an interval of 4 to 8 hours. If the response is still inadequate, a final bolus screening dose of 100 micrograms in 2 milliliters may be administered 24 hours later. Pediatric Patients: The starting screening dose for pediatric patients is the same as in adult patients, i.e., 50 mcg. However, for very small patients, a screening dose of 25 mcg may be tried first. Patients who do not respond to a 100 mcg intrathecal bolus should not be considered candidates for an implanted pump for chronic infusion . Post-Implant Dose Titration Period: To determine the initial total daily dose of baclofen injection (intrathecal) following implant, the screening dose that gave a positive effect should be doubled and administered over a 24-hour period, unless the efficacy of the bolus dose was maintained for more than 8 hours, in which case the starting daily dose should be the screening dose delivered over a 24-hour period. No dose increases should be given in the first 24 hours (i.e., until the steady state is achieved). Adult Patients with Spasticity of Spinal Cord Origin: After the first 24 hours, for adult patients, the daily dosage should be increased slowly by 10 to 30% increments and only once every 24 hours, until the desired clinical effect is achieved. Adult Patients with Spasticity of Cerebral Origin: After the first 24 hours, the daily dose should be increased slowly by 5 to 15% only once every 24 hours, until the desired clinical effect is achieved. Pediatric Patients: After the first 24 hours, the daily dose should be increased slowly by 5 to 15% only once every 24 hours, until the desired clinical effect is achieved. If there is not a substantive clinical response to increases in the daily dose, check for proper pump function and catheter patency. Patients must be monitored closely in a fully equipped and staffed environment during the screening phase and dose-titration period immediately following implant. Resuscitative equipment should be immediately available for use in case of life-threatening or intolerable side effects. Maintenance Therapy: Spasticity of Spinal Cord Origin Patients: The clinical goal is to maintain muscle tone as close to normal as possible, and to minimize the frequency and severity of spasms to the extent possible, without inducing intolerable side effects. Very often, the maintenance dose needs to be adjusted during the first few months of therapy while patients adjust to changes in life style due to the alleviation of spasticity. During periodic refills of the pump, the daily dose may be increased by 10 to 40%, but no more than 40%, to maintain adequate symptom control. The daily dose may be reduced by 10 to 20% if patients experience side effects. Most patients require gradual increases in dose over time to maintain optimal response during chronic therapy. A sudden large requirement for dose escalation suggests a catheter complication (i.e., catheter kink or dislodgement). Maintenance dosage for long term continuous infusion of baclofen injection (intrathecal) has ranged from 12 mcg/day to 2,003 mcg/day, with most patients adequately maintained on 300 micrograms to 800 micrograms per day. There is limited experience with daily doses greater than 1,000 mcg/day. Determination of the optimal baclofen injection (intrathecal) dose requires individual titration. The lowest dose with an optimal response should be used. Spasticity of Cerebral Origin Patients: The clinical goal is to maintain muscle tone as close to normal as possible and to minimize the frequency and severity of spasms to the extent possible, without inducing intolerable side effects, or to titrate the dose to the desired degree of muscle tone for optimal functions. Very often the maintenance dose needs to be adjusted during the first few months of therapy while patients adjust to changes in life style due to the alleviation of spasticity. During periodic refills of the pump, the daily dose may be increased by 5 to 20%, but no more than 20%, to maintain adequate symptom control. The daily dose may be reduced by 10 to 20% if patients experience side effects. Many patients require gradual increases in dose over time to maintain optimal response during chronic therapy. A sudden large requirement for dose escalation suggests a catheter complication (i.e., catheter kink or dislodgement) . Maintenance dosage for long term continuous infusion of baclofen injection (intrathecal) has ranged from 22 mcg/day to 1,400 mcg/day, with most patients adequately maintained on 90 micrograms to 703 micrograms per day. In clinical trials, only 3 of 150 patients required daily doses greater than 1,000 mcg/day. Pediatric Patients: Use same dosing recommendations for patients with spasticity of cerebral origin. Pediatric patients under 12 years seemed to require a lower daily dose in clinical trials. Average daily dose for patients under 12 years was 274 mcg/day, with a range of 24 to 1,199 mcg/day. Dosage requirement for pediatric patients over 12 years does not seem to be different from that of adult patients. Determination of the optimal baclofen injection (intrathecal) dose requires individual titration. The lowest dose with an optimal response should be used. Potential need for dose adjustments in chronic use: During long term treatment, approximately 5% (28/627) of patients become refractory to increasing doses. There is not sufficient experience to make firm recommendations for tolerance treatment; however, this “tolerance” has been treated on occasion, in hospital, by a “drug holiday” consisting of the gradual reduction of baclofen injection (intrathecal) over a 2 to 4 week period and switching to alternative methods of spasticity management. After the “drug holiday,” baclofen injection (intrathecal) may be restarted at the initial continuous infusion dose. Stability Parenteral drug products should be inspected for particulate matter and discoloration prior to administration, whenever solution and container permit. Delivery Specifications The specific concentration that should be used depends upon the total daily dose required as well as the delivery rate of the pump. Baclofen injection (intrathecal) may require dilution when used with certain implantable pumps. Please consult manufacturer's manual for specific recommendations. Preparation Instruction: Screening Use the 1 mL screening ampule only (50 mcg per mL) for bolus injection into the subarachnoid space. For a 50 mcg bolus dose, use 1 mL of the screening ampule. Use 1.5 mL of 50 mcg per mL baclofen injection (intrathecal) for a 75 mcg bolus dose. For the maximum screening dose of 100 mcg, use 2 mL of 50 mcg per mL baclofen injection (intrathecal) (2 screening ampules). Maintenance For patients who require concentrations other than 500 mcg per mL or 2,000 mcg per mL, baclofen injection (intrathecal) must be diluted. Baclofen injection (intrathecal) must be diluted with sterile preservative free Sodium Chloride for Injection, U.S.P. Delivery Regimen: Baclofen injection (intrathecal) is most often administered in a continuous infusion mode immediately following implant. For those patients implanted with programmable pumps who have achieved relatively satisfactory control on continuous infusion, further benefit may be attained using more complex schedules of baclofen injection (intrathecal) delivery. For example, patients who have increased spasms at night may require a 20% increase in their hourly infusion rate. Changes in flow rate should be programmed to start two hours before the time of desired clinical effect.

"The most common is transient drowsiness," reported in up to 63% of patients in some trials. Other common reactions include dizziness (5-15%), weakness (5-15%), and fatigue (2-4%); less common effects include nausea, headache, confusion, and hypotension.