G
gabapentin
Brand Name(s): Neurontin
Clinical Pharmacology:Mechanism of Action: An anticonvulsant and antineuralgic agent whose exact mechanism is unknown. May increase the synthesis or accumulation of gamma-aminobutyric acid by binding to as-yet-undefined receptor sites in brain tissue. Therapeutic Effect: Reduces seizure activity and neuropathic pain.
Pharmacokinetics: Well absorbed from the GI tract (not affected by food). Protein binding: less than 5%. Widely distributed. Crosses the blood-brain barrier. Primarily excreted unchanged in urine. Removed by hemodialysis. Half-life: 5-7 hr (increased in impaired renal function and the elderly).
Available Forms:
Indications and Dosages:Adjunctive therapy for seizure control: PO Initially, 300 mg 3 times a day. May titrate dosage. Range: 900-1800 mg/day in 3 divided doses. Maximum: 3,600 mg/day.
Adjunctive therapy for neuropathic pain: PO Initially, 100 mg 3 times a day; may increase by 300 mg/day at weekly intervals. Maximum: 3,600 mg/day in 3 divided doses.
Postherpetic neuralgia: PO 300 mg on day 1, 300 mg twice a day on day 2, and 300 mg 3 times a day on day 3. Titrate up to 1,800 mg/day.
Dosage in renal impairment: Dosage and frequency are modified based on creatinine clearance:
| Creatinine Clearance | Dosage |
|---|---|
| 60 ml/min or higher | 400 mg q8h |
| 30-59 ml/min | 300 mg q12h |
| 16-29 ml/min | 300 mg daily |
| less than 16 ml/min | 300 mg every other day |
| Hemodialysis | 200-300 mg after each 4-hr hemodialysis session |
Unlabeled Uses: Treatment of bipolar disorder, chronic pain, diabetic peripheral neuropathy, essential tremor, hot flashes, hyperhidrosis, migraines, psychiatric disorders (social phobia)
Contraindications: None known.
Side Effects
Serious Reactions
Patient/Family Education
Monitoring Parameters
Geriatric side effects at a glance:
Use with caution in older patients with: Renal impairment, Urinary incontinence
U.S. Regulatory Considerations
Other Uses in Geriatric Patient: Neuropathic Pain, Post-Herpetic Neuralgia, Essential Tremor
Side Effects:
Geriatric Considerations – Summary: Dosage adjustments required in older adults with creatinine clearance < 60 ml/min. Gabapentin has been well-studied in older adults and is considered a first-line agent as a result of tolerability, small effects on cognition, and few drug interactions. Absorption is reduced by approximately 50% at doses > 3600 mg/day. Capsules are large and may be difficult to swallow, especially in patients with dysphagia or dry mouth.1 Brodie M, Kwan P. Epilepsy in elderly people. BMJ. 2005;331:1317-1322.
2 Rowan AJ, Ramsay RE, Collins JF, et al. New onset geriatric epilepsy: a randomized study of gabapentin, lamotrigine, and carbamazepine. Neurology. 2005;64:1868-1873.
3 Arroyo S, Kramer G. Treating epilepsy in the elderly: safety considerations. Drug Safety. 2001;24:991-1015.
4 Drugs that may cause cognitive disorders in the elderly. Med Lett. 2000;42:111-112.
5 Willmore LJ. Choice and use of newer anticonvulsant drugs in older patients. Drugs Aging. 2000;17:441-452.
6 Faught E. Epidemiolgy and drug treatment of epilepsy in elderly people. Drugs Aging. 1999;15:255-269.
galantamine hydrobromide
(ga-lan’-ta-meen hye-droe-broe’-mide)
Brand Name(s): Razadyne, Razadyne ER
Clinical Pharmacology:Mechanism of Action: A cholinesterase inhibitor that inhibits the enzyme acetylcholinesterase, thus increasing the concentration of acetylcholine at cholinergic synapses and enhancing cholinergic function in the CNS. Therapeutic Effect: Slows the progression of Alzheimer’s disease.
Pharmacokinetics: Rapidly absorbed from the GI tract. Protein binding: 18%. Distributed to blood cells; binds to plasma proteins, mainly albumin. Metabolized in the liver. Excreted in urine. Half-life: 7 hr.
Available Forms:
Indications and Dosages:Alzheimer’s disease: PO Initially, 4 mg twice a day (8 mg/day). After a minimum of 4 wk (if well tolerated), may increase to 8 mg twice a day (16 mg/day). After another 4 wk, may increase to 12 mg twice daily (24 mg/day). Range: 16-24 mg/day in 2 divided doses. PO (Extended Release) 8-24 mg/day as a single daily dose.
Dosage in renal or hepatic impairment: For moderate impairment, maximum dosage is 16 mg/day. Drug is not recommended for patients with severe impairment.
Contraindications: Severe hepatic or renal impairment
Side Effects
Serious Reactions
Patient/Family Education
• Patient and caregiver should be advised of high incidence of gastrointestinal effects and directions for resource and resolution
• Avoid tasks that require mental alertness or motor skills until response to the drug has been established
• Notify the physician if excessive sweating, tearing, salivation, depression, dizziness, excessive fatigue, muscle weakness, insomnia, or persistent GI disturbances occur
Monitoring Parameters
• Cognitive function (e.g., ADAS, Mini-Mental Status Exam [MMSE]), activities of daily living, global functioning, blood chemistry, complete blood counts, heart rate, blood pressure
• Assess the patient for signs of GI distress, including nausea, vomiting, diarrhea, anorexia, and weight loss
Geriatric side effects at a glance:
Use with caution in older patients with: None
U.S. Regulatory Considerations
Other Uses in Geriatric Patient: None
Side Effects:
Geriatric Considerations – Summary: Galantamine, like other cholinesterase inhibitors, is modestly effective for treatment of cognitive decline associated with Alzheimer’s disease. Compared to placebo, persons using galantamine have less decline in performance on cognitive tests, but most patients derive minimal clinical benefit, and there is no evidence the drug delays disability or institutionalization. Galantamine is expensive, and not cost-effective for this indication. Persons using drugs to treat Alzheimer’s disease should be monitored closely, and prescribers should have a low threshold for discontinuing these agents if no clinical benefit is observed.ganciclovir sodium
(gan-sye’-kloe-veer soe’-dee-um)
Brand Name(s): Cytovene, Vitrasert
Clinical Pharmacology:Mechanism of Action: This synthetic nucleoside competes with viral DNA polymerase and is incorporated into growing viral DNA chains. Therapeutic Effect: Interferes with synthesis and replication of viral DNA.
Pharmacokinetics: Widely distributed. Protein binding: 1%-2%. Undergoes minimal metabolism. Excreted unchanged primarily in urine. Removed by hemodialysis. Half-life: 2.5-3.6 hr (increased in impaired renal function).
Available Forms:
Indications and Dosages:Cytomegalovirus (CMV) retinitis: IV 10 mg/kg/day in divided doses q12h for 14-21 days, then 5 mg/kg/day as a single daily dose or 6 mg/kg 5 days a week.
Prevention of CMV disease in transplant patients: IV 10 mg/kg/day in divided doses q12h for 7-14 days, then 5 mg/kg/day as a single daily dose.
Other CMV infections: IV Initially, 10 mg/kg/day in divided doses q12h for 14-21 days, then 5 mg/kg/day as a single daily dose. Maintenance: 1000 mg 3 times a day or 500 mg q3h (6 times a day). Intravitreal implant 1 implant q6-9mo plus oral ganciclovir.
Unlabeled Uses: Treatment of other CMV infections, such as gastroenteritis, hepatitis, and pneumonitis
Contraindications: Absolute neutrophil count less than 500/mm3, platelet count less than 25,000/mm3, hypersensitivity to acyclovir or ganciclovir, immunocompetent patients, patients with congenital CMV disease
Side Effects
Serious Reactions
• Intra-ocular insertion occasionally results in visual acuity loss, vitreous hemorrhage, and retinal detachment.
Patient/Family Education
• Male patients should be aware that ganciclovir may temporarily or permanently inhibit sperm production
• Male patients should use barrier contraception during ganciclovir therapy and for 90 days afterward because of the drug’s mutagenic potential
Monitoring Parameters
Geriatric side effects at a glance:
U.S. Regulatory Considerations
gatifloxacin
Brand Name(s): Tequin, Tequin Teqpaq, Zymar
Clinical Pharmacology:Mechanism of Action: A fluoroquinolone that inhibits two enzymes, topoisomerase II and IV, in susceptible microorganisms. Therapeutic Effect: Interferes with bacterial DNA replication. Prevents or delays resistance emergence. Bactericidal.
Pharmacokinetics: Well absorbed from the GI tract after PO administration. Protein binding: 20%. Widely distributed. Metabolized in liver. Primarily excreted in urine. Half-life: 7-14 hr.
Available Forms:
Indications and Dosages:Chronic bronchitis, complicated urinary tract infections, pyelonephritis, skin infections: PO, IV 400 mg/day for 7-10 days (5 days for chronic bronchitis).
Urethral gonorrhea in men and women, endocervical and rectal gonorrhea in women: PO, IV 400 mg as a single dose.
Topical treatment of bacterial conjunctivitis due to susceptible strains of bacteria: Ophthalmic 1 drop q2h while awake for 2 days, then 1 drop up to 4 times/day for days 3-7.
Dosage in renal impairment:
| Creatinine Clearance | Dosage |
|---|---|
| 40 ml/min | 400 mg/day |
| less than 40 ml/min | Initially, 400 mg/day, then 200 mg/day |
| Hemodialysis | Initially, 400 mg/day, then 200 mg/day |
| Peritoneal dialysis | Initially, 400 mg/day, then 200 mg/day |
Contraindications: Hypersensitivity to quinolones
Side Effects
Abdominal pain, constipation, dyspepsia, stomatitis, edema, insomnia, abnormal dreams, diaphoresis, altered taste, rash
Serious Reactions
• Pseudomembranous colitis, as evidenced by severe abdominal pain and cramps, severe watery diarrhea, and fever, may occur.
• Superinfection, manifested as genital or anal pruritus, ulceration or changes in oral mucosa, and moderate to severe diarrhea, may occur.
Patient/Family Education
• Should be taken at least 4 hr before or 8 hr after multivitamins (containing iron or zinc), antacids (containing magnesium, calcium, or aluminum), sucralfate, or didanosine chewable/buffered tablets
• Discontinue treatment, rest and refrain from exercise, and inform prescriber if pain, inflammation, or rupture of a tendon occurs
• Test reaction to this drug before operating an automobile or machinery or engaging in activities requiring mental alertness or coordination
Monitoring Parameters
• Evaluate for abdominal pain, altered sense of taste, dyspepsia (heartburn, indigestion), headache, and vomiting
• Daily bowel activity and stool consistency. Although mild GI effects may be tolerable, severe symptoms may indicate the onset of antibiotic-associated colitis.
• Signs and symptoms of superinfection include abdominal pain or cramping, anal or genital pruritus or discharge, moderate to severe diarrhea, severe mouth or tongue soreness, and new or increased fever.
Geriatric side effects at a glance:
U.S. Regulatory Considerations
gemfibrozil
Brand Name(s): Lopid
Clinical Pharmacology:Mechanism of Action: A fibric acid derivative that inhibits lipolysis of fat in adipose tissue; decreases liver uptake of free fatty acids and reduces hepatic triglyceride production. Inhibits synthesis of VLDL carrier apolipoprotein B. Therapeutic Effect: Lowers serum cholesterol and triglycerides (decreases VLDL, LDL; increases HDL).
Pharmacokinetics: Well absorbed from the GI tract. Protein binding: 99%. Metabolized in liver. Primarily excreted in urine. Not removed by hemodialysis. Half-life: 1.5 hr.
Available Forms:
Indications and Dosages:
Contraindications: Liver dysfunction (including primary biliary cirrhosis), preexisting gallbladder disease, severe renal dysfunction
Side Effects
Serious Reactions
Patient/Family Education
• May cause dizziness or blurred vision; use caution while driving or performing other tasks requiring alertness
Monitoring Parameters
• Assess the patient for pain, especially in the right upper quadrant of the abdomen, because epigastric pain may indicate cholecystitis or cholelithiasis
Geriatric side effects at a glance:
U.S. Regulatory Considerations
gemifloxacin mesylate
(gem-ah-flox’-a-sin mes’-sil-ate)
Brand Name(s): Factive
Clinical Pharmacology:Mechanism of Action: A fluoroquinolone that inhibits the enzyme DNA gyrase in susceptible microorganisms, interfering with bacterial cell replication and repair. Therapeutic Effect: Bactericidal.
Pharmacokinetics: Rapidly and well absorbed from the GI tract. Protein binding: 70%. Widely distributed. Penetrates well into lung tissue and fluid. Undergoes limited metabolism in the liver. Primarily excreted in feces; lesser amount eliminated in urine. Partially removed by hemodialysis. Half-life: 4-12 hr.
Available Forms:
Indications and Dosages:| Creatinine Clearance | Dosage |
|---|---|
| greater than 40 ml/min | 320 mg once a day |
| 40 ml/min or less | 160 mg once a day |
Contraindications: Concurrent use of amiodarone, quinidine, procainamide, or sotalol; history of prolonged QTc interval; hypersensitivity to fluoroquinolones; uncorrected electrolyte disorders (such as hypokalemia and hypomagnesemia)
Side Effects
Serious Reactions
• Hypersensitivity reactions, including photosensitivity (as evidenced by rash, pruritus, blisters, edema, and burning skin), have occurred.
Patient/Family Education
• Should not be taken within 3 hr of multivitamins (containing iron or zinc), antacids (containing magnesium, calcium, or aluminum), sucralfate, or didanosine chewable/buffered tablets
• Discontinue treatment, rest and refrain from exercise, and inform prescriber if pain, inflammation, or rupture of a tendon occurs
• Test reaction to this drug before operating an automobile or machinery or engaging in activities requiring mental alertness or coordination
Monitoring Parameters
• Daily bowel activity and stool consistency. Although mild GI effects may be tolerable, severe symptoms may indicate the onset of antibiotic-associated colitis.
• Signs and symptoms of superinfection include abdominal pain or cramping, anal or genital pruritus or discharge, moderate to severe diarrhea, severe mouth or tongue soreness, and new or increased fever.
Geriatric side effects at a glance:
U.S. Regulatory Considerations
gentamicin sulfate
Brand Name(s): Garamycin, Garamycin Ophthalmic, Garamycin Topical, Genoptic, Gentacidin, Gentak, Ocu-MycinRx: with prednisolone (Pred-G)
Chemical Class: Aminoglycoside
Clinical Pharmacology:Mechanism of Action: An aminoglycoside antibacterial that irreversibly binds to the protein of bacterial ribosomes. Therapeutic Effect: Interferes with protein synthesis of susceptible microorganisms. Bactericidal.
