Interacting drugs - summary

+ Gabapentin
             
Antacids                                                                                                                       Antacids reduced the bioavailability of gabpentin by about 20%.
Take at least  2 hours following antacid administration.

Cimetidine                                                                                                                  cimetidine alter the renal excretion of both gabapentin and  creatinine.
 Not clinically important

Contraceptives Oral-                                                                                                       Cmax of norethidone 13% higher when coadministered with gababapentin,
 Interaction not of clinical importance


 

Body as a whole- Fatigue, Weight increase, Back pain, Peripheral edema

GI- Dyspepsia, Dryness of mouth /throat,Constipation, Dental abnormalities,Increased appetite

Musculoskeltal- Myalgia, Fracture

Respiratory- Rhinitis, Pharyngitis, Ciughing

Special senses- Diplopia, Amblyopia

Cardiovascular- Hypertension, Hypotension, angina pectoris, peripheral vascular disorder, tachycardia,  migraine,  murmur, atrial fibrillation, heart faliure, thrombophlebitis, deep vein thrombophlebitis,   myocardial infarction

CNS- Somnolence, dizziness, ataxia, nystagmus, nervousness, dysarthria, amnesia, depression,  abnormal thinking, twiching, abnormal coordination

Dermatologic- Pruritus, abrasion

Miscellaneous- Impotence, leukopenia, WBC decreased, vasodilation

Hypersens. Special precautions:

Discontinuation or transfer from other antiepileptics, pregnancy and lactation,children below 12 years. Monitoring- clinical trials data do not indicate that routine monitoring of clinical laboratory parameters is necessary for the safe use of gabapentin.

Warnings-

Withdrawal- precipitated seizure- antiepileptic drugs should not be abruptly discontinued because of the possibility of increasing seizure frequency

Status epilepticus- becuase adequate historical data are not avialable it is impossible to say whether or not treatment with gabapentin is associated with a higher or lower rate of status epilepticus than would be expected to occur in a similar population not treated with gabapentin.

Sudden and unexplained deaths- during the course of premarketing development of gabapentin, eight sudden and unexplained deaths were recorded among 2203 patients. Some of these could represent seizure-related deaths in which the seizure was not observed. (eg. at night)

Carcinogenesis-

Clinical experience during gabapentins premarketing development provides no direct means to assess its potential for inducing tumors in humans.

Elderly- no systemic studies in geriatric patients have been conducted. The small number of older individuals evaluted however, limits the strength of any conclusions reached about the influence, if any, of age, on any kind of adverse events or laboratory abnormalities associated with gabapentin.

Pregnancy- use during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Lactation- use in women who are nursing only if the benefits clearly outweigh the risks.

Children- safety and efficay in children < 12 years have not been established

Adjunctive treatment of potential seizures

Dosage

Adults and children over 12 yrs- 900 to 1800mg day upto 2400mg day in 3 equally divided doses Recommended build up 300 to 400mg once a day on day 1, twice on day 2, and three times on day 3. Further additions being made on a similar pattern according to clinical response.

Overdosage- Symptoms

Acute oral overdose of gabapentin uo to 49g have been reported.. In these cases double vision,slurred speech, drowsiness, lethargy and diarrhea were observed. All patients recoverd with supportive care.

Treatment

1. Gabapentin can be removed by hemodialysis

2. Although hemodialysis has not been performed in the few overdose cases reported,it may be indicated by the patients clinical state or in patients with significant renal impairment.

Missed dose-

1. If you miss a dose of this medicine, take it as soon as possible.

2. However, if it is almost time for next dose, skip the missed dose and go back to your regular dosing schedule.

3. Do not double doses.

EVIDENCE BASED MEDICINE (MIMS April 2003)

Post-herpetic Neuralgia Comparitive effectiveness of various interventions Prevention of post-herpetic neuralgia

Beneficial

1. Oral antiviral agents such as acyclovir, famciclovir, valaciclovir, netivudine

2. Tricyclic antidepressants (amitriptyline)

Unknown effectiveness

1. Levodopa

2. Amantadine

3. Isoprinosine

4. Adenosine monophosphate Unlikely to be beneficial

1. Topical antiviral agents (idoxurine) for relief of acute oain only

2. Cimetidine

Ineffective or harmful

1. Corticosteroids Relieving established post-herpetic neuralgia Beneficial

1. Tricyclic antidepressants (amitriptyline)

2. Oxycodone (opiod)

3. Gabapentin (anticonvulasant) Unknown effectiveness

1. Capsaicin (topical counterirritant)

2. Topical lignocaine

Ineffective or harmful

1. Epidural morphine

2. Dextromethorphan

KEY POINTS

1. Daily acyclovir reduced the relative risk of of post-herpetic pain at six months by about 50 % compared with placebo

2. Famciclovir significantly reduced pain duration after acute herpes zoster.

3. Idoxuridine was associated with short term pain relief in acute herpes zoster but did not prevent post-herpetic neuralgia

4. Conflicting evidence on whether corticosteroids alone prevent post-herpetic neuralgia. Limited evidence that high dose steroids and antiviral agents combined may speed healing of acute zoster. No evidence that it reduces post-herpetic neuralgia 5. Amitriptyline started during the acute episode reduced prevalence of post-herpetic neuralgia at six months. 6. Insufficient evidence on the effect of other drug treatment.

1. Take gabapentin only as prescribed.

2. May cause dizziness,somnolence,and other signs of CNS depression. Patients advised not to drive cars or operate complex machinery.

3. Allergies- Tell your doctor if you have ever had any unusual or allergic reactions to Gabapentin or related medicines. Also tell your doctor if your are allergic to any other substances such as foods, preservatives or dyes.

4. Pregnancy- before taking this medicine make sure that your doctor knows if you are pregnant or if you may become pregnant.

5..Breast feeding- mothers who are taking this medicine and who want to breat feed should discuss this with their doctor.

6.Children- no specific information comparing use of gabapentin inchildren with other age groups In teenagers betwen 12 to 18 years of age gabapentin has not been shown to cause different side effects or problems than it does in adults

7. Elderly- not shown to cause different problems in elderly people than in younger adults.

8. Tell your doctor

if you are taking any of the following- Antacids - lower blood levels of gabapentin may occur> Gabapentin should be taken at least 2 hours after any antacid is taken

9. Other medical problems- presence of other medical problems may affect the use of this medicine- Kidney disease - higher blood levels of gabapentin may occur which may increase the chances of unwanted effects. Your doctor may need to change the dose

10. Missed dose- If you miss a dose of this medicine take it as soon as possible. However if it is almost time for your next dose go back to your regular dosing schedule. Do not double dos

ANTICONVULSANTS INCLUDES -

BARBITURATES - OXAZOLIDINEDIONES- MISCELLANEOUS- Phenobarbitone Paramethadione Lamotrigine Trimethadione Primidone

HYDANTOINS-

Valproic acid Phenytoin BENZODIAPINES- Cabamazepine Mephenytoin Clonazepam Phenacemide Ethotoin Clorazepate Felbamate Diazepam Gabapentin SUCCINIMIDES- Ethosuximide Methsuximide Phensuximide REFER PHENYTOIN SODIUM - 

Pharmacology:

Gabapentin is an oral antiepileptic agent. Thr mechanism of action is not clearly understood. Pharmcokinetics: Gabapentin bioavailability is not dose-related, and food has no effect on the rate and extent of absorption. It is eliminated from the sytemic circulation by renal exctretion as unchanged drug. It is not apprciably metabolised.

Not significant.

Pregnancy-

Use during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Lactation-

Use in women who are nursing only if the benefits clearly outweigh the risks.

Children-

Safety and efficay in children < 12 years have not been established