Drugs: Therapeutic Levels

What are the therapeutic and toxic levels of the following commonly prescribed drugs?

1. Acetaminophen (Tylenol)
2. Alcohol (Ethanol)
3. Amitryptiline (Elavil)
4. Carbamazepine (Tegretol)
5. Diazepam (Valium)
6. Digitoxin
7. Digoxin
8. Imipramine (Tofranil)
9. Lithium
10. Lidocaine (Xylocaine)
11. Methotrexate
12. Phenobarbital
13. Phenytoin (Dilantin)
14. Procainamide (Promestyl)
15. Quinidine
16. Theophylline
17. Valproic Acid (Depakene)

ANSWERS and a few important facts about some of the medications:

1. Acetaminophen (Tylenol) - Non-narcotic analgesic
Therepeutic: 1-30mcg/ml
Toxic: >200mcg/ml
Action: Analgesic and antipyretic; but does not have anti-inflammatory or antiplatelet action. Antiprostaglandin activity reduces fever; causes peripheral vasodilation.
Use: Mild to moderate pain
S/E: GI irritation; Occult bleeding; tinnitus, dizziness, confusion; Liver dysfunction
Nsg. Considerations:
a. Monitor liver & kidney function, and CBC periodically for clients on long-term therapy.
b. Can cause psychologic dependence
Antidote: Acetylcysteine (Mucomyst)
Discharge Teaching: Notify provider if no relief of symptoms within 5 days of therapy.

2. Alcohol (Ethanol)
Therapeutic: 100 mcg/ml
Toxic : >400mcg/ml

3. Amitryptiline (Elavil) - TCA (Tricyclic antidepressant)
Therapeutic: 120-250 mcg/ml
Toxic: 500 mcg/ml
Action: Structurally related to phenathiazines. Blocks reuptake of the neurotransmitters norepinephrine and serotonin at the neuronal memberane, which increases and prolongs the response of the neurotransmitters.
Use: Endogenous and reactive depression
S/E: Sedation, confusion; anticholinergic effects; orthostatic hypotension; arrhythmias; clients recovering from MI should not take this drug; blood dyscrasias; EPS; gynecomastia; jaundice
Nsg. Considerations:
a. May take 2-4 weeks to achieve therapeutic effects. Monitor for suicidal tendencies
b. Monitor CBC on long-term use
c. Monitor I & O
d. Drug therapy is discontinued gradually

4. Carbamazepine (Tegretol) - Anti-convulsant; Bipolar Disorder Drug
Therapeutic: 8-12mcg/ml
Toxic: 15mcg/ml
Action: Chemically similar to TCA's
Use: Treatment of tonic-clonic, complex partial, and mixed seizures
S/E: Myelosuppresion; Dizziness, drowsiness: Ataxia; Diplopia, rash
Nsg. Considerations:
a. Monitor I & O
b. Supervise ambulation
c. Monitor CBC
d. Take with meals
e. Wear protective clothing due to photosensitivity

5. Diazepam (Valium) - Benzodiazepines; Anti-anxiety; Anti-convulsant
Action: Not fully understood. Depresses the CNS at the limbic system and reticular formation.
Use: Anxiety disorders, acuted alcohol withdrawal, muscle relaxant, tetanus, convulsive disorders, preoperative medication
S/E: Drowsiness, ataxia; hypotension; tachycardia; Respiratory depression
A/E: Dry mouth, constipation, urinary retention, photophobia and blurred vision.
Nsg. Considerations:
a. Adverse effects typically dose related
b. Two weeks of therapy needed before steady plasma levels seen
c. Do not mix with other drugs in the same syringe
d. Cautious IV use as drug can precipitate in IV solutions
e. IM shoud be deep into large muscles; rotate IM sites
f. IV push doses shouldn't exceed 2mg/minute
g. Parenteral administration can cause low blood pressure, increased HR, muscle weakness, and resp. depression
h. Alcohol increases CNS depression
h.After long-term use, withdrawal leads to Sxs such as vomiting, sweating, cramps, tremors, and possibly convulsions.

6. Digitoxin (Crystodigin) - Cardiac glycoside
Therapeutic: 20-35ng/ml
Toxic: >45ng/ml

7. Digoxin (Lanoxin, Lanoxicaps) - Cardiac glycoside
Therapeutic: 08-1.5mcg/ml
Toxic: >2mcg/ml
Action: Increases force of myocardial contraction and slows heart rate by stimulating the vagus nerve and blocking the AV node.
Use: CHF, atrial tachycardia, atrial fibrillation, and atrial flutter.
C/I: with ventricular dysrhythmias and second or third-degree heart block
S/E: Anorexia, nausea, vomiting; tachycardia, bradycardia; yellow-green halos around dark objects; dysrhythmias; drowsiness; photophobia
Nsg. Considerations:
a. Monitor for digitalis toxicity
b. Risk of digitalis toxicity increases if patient is hypokalemic, with hypercalcemia, hypothyroidism, hypomagnesemia.
c.Take AP for 1 full minute before administering. Notify provider if AP <60>

8. Imipramine (Tofranil)- Anti-psychotic (TCA)
Therapeutic: 125-250mcg/ml
Toxic: >500mcg/ml
* see Amitryptiline (Elavil)

9. Lithium - Lithium carbonate (Eskalith) - Anti-psychotic
Related drug: Lithium citrate (Cibalith-S) available in liquid form
Therapeutic: 0.6-1.2mcg/ml
Toxic: >2mcg/ml
Action: Exact mode of action is unknown. Thought to alter neurotransmitter in CNS that produce anti-depressant and anti-manic effects.
Use: Treatment and prophylaxis of manic phase of bipolar disorder
A/E: Confusion, restlessnes, fatigue, weakness, hand tremors; arrhythmias, circulatory collapse, palpitations, hypotension; blurred vision; dry mouth, thirst, weight gain; nausea, diarrhea; leukocytosis
Nsg. Considerations:
a. Monitor for lithium levels (blood test done monthly)
b. Monitor for lithium intoxication
c. Treatment for lithium intoxication includes: IV therapy with normal saline, diuretics, and hemodialysis
d. Monitor thyroid function studies periodically
e. May take 1-2 weeks to achieve therapeutic effects.
Discharge Teachings:
a. Drink 2-3 liters of fluid per day to relieve thirst and dry mouth
b. Maintain sodium intake of 6-10g daily to reduce lithium toxicity
c. Take with food to decrease GI distress
d. Do not drive or operate machinery until drug response established
e. Report to provider: nausea, vomiting, edema, weight gain, tremors and drowsiness ( signs of lithium toxicity or hypothyroidism)

10. Lidocaine (Xylocaine) - Local Anesthetic; Anti-arrhythmic
Therapeutic: 1.5-6mcg/ml
Toxic: > 6-8mcg/ml
Action: Interferes with electrical excitability of the heart
Use: PVC's, acute ventricular arrhythmias
S/E: Hypotension, tremors; double vision; tinnitus; confusion, blurred vision; drowsiness; dizziness
Nsg. Considerations:
a.Observe carefully for signs of CNS toxicity (confusion, tremors)
b. Monitor cardiac function and BP
c. Use infusion pump for IV administration; IM may increase CPK levels
d.Give O2
e. Check BUN, creatinine

11. Methotrexate with Leucovorin rescue - Antimetabolite
Therapeutic: variable
Toxic: >454 mcg/ml
Action: Leucovorin calcium is a folic acid analog that interferes with mitotic process by blocking folinic acid.
Use: Acute lymphoblastic leukemia; cancer of the breast, lung, testes, ovary, head and neck; choriocarcinoma
S/E: Nausea, vomiting; diarrhea; oral ulceration; hepatic dysfunction; bone marrow suppression; renal dysfunction; alopecia
Nsg. Considerations:
a. Monitor hamatopoietic function
b. Good mouth care
c. Small frequent feedings
d. Counsel about body image changes (alopecia); provide wig
e. Good skin care

12. Phenobarbital (luminal) - Barbiturate; Sedative; Hypnotic
Therapeutic: 15-40 mcg/ml
Toxic: 35-80 mcg/ml
Action: Hinders movement of impulses from the thalamus to the brain cortex, thus creating depression in the CNS, which can range from mild to severe. Considered a long-acting barbiturate.
Use: Sedation; hypnosis; seizure disorders
S/E: Drowsiness, rash; GI upset; Initially constricts pupils; Respiratory depression; ataxia
Nsg. Considerations:
a. Monitor V/S - resuscitation equipment should be available if given IV
b.Drowsiness diminishes after initial week of therapy
c. Instruct not to take alcohol or perform hazardous activities
d. Nystagmus may indicate early toxicity
e. Sudden discontinuation may lead to withdrawal
f. Tolerance and dependence result from long-term use
g. Folic acid supplements are indicated for long-term use

13. Phenytoin (Dilantin) - Hydantoin; Anti-convulsant
Therapeutic: 10-20 mcg/ml
Toxic: variable
Action: Prevents dissemination of electrical discharges in motor cortex area of the brain.
Use: Tonic-clonic and complex partial seizures; status epilepticus, prevention of seizures that accompany neurosurgery
S/E: Drowsiness, ataxia; nystagmus; blurred vision; hirsutism; lethargy; GI upset; gingival hypertrophy
Nsg. Considerations:
a. Give oral medication with at leat 1/2 glass of water or with meals to minimize GI irritation
b. Inform client that red-brown or pink discoloration of sweat and urine may occur
c. IV administration may lead to cardiac arrest -- have resuscitation equipment at hand
d. Never mix with any other drug or dextrose IV
e. Instruct for oral hygiene
f. Increase Vit. D intake and exposure to sunlight may be necessary for long-term use
g. Alcohol increases serum levels

14. Procainamide (Promestyl, Procan SR) - Anti-arrhytmias
Therapeutic: 5-12 mcg/ml
Toxic: >15 mcg/ml
Action: Depresses ectopic pacemakers; action on the heart is similar to Quinidine.
Use: PVC's; ventricular tachycardia, and some atrial arrhythmias.
S/E: Hypotension; bradycardia; fever, rash; nausea & vomiting; dizziness; neutropenia
Nsg. Considerations:
a. Use infusion pump for IV administration
b. Monitor potassium levels, CBC
c. Patient must be on a cardiac monitor
d. Monitor BP frequently
e. Teach patient to check pulse

15. Quinidine (Quinaglute) - Anti-arrhytmia
Therapeutic: 2-6 mcg/ml
Toxic: >8 mcg/ml
Action: Depresses myocardial excitability; slows conduction time in atria and ventricles, prolongs PR interval and QRS complex; prolongs refractory period; depresses myocardial contractility, reduces vagal tone.
Use: Atrial fibrillation and flutter ventricular tachycardia
S/E: Anemia; hypotension; headache; heart block; tinnitus, fever; GI symptoms Nsg. Considerations:
a. May increase toxcity for digitalis
b. Monitor liver function tests and I & O
c. Check apical pulse and BP
d. Monitor EKG and BP
e. Advise clients to report dizziness or faintness immediately
f. Administer drug with food to minimize GI symptoms (N & V)
g. Instruct client to avoid fatigue, excessive caffeine, alcohol, smoking, heavy meals, stressful situations, OTC drugs

16. Theophylline - Anti-asthma; Bronchodilator
Related Drugs: Aminophylline (Somophyllin); Theo-dur; Slow-Bid Gyrocaps; Quibron; Elixophylline - (less potent); Dyphylline (Dilor)
Therapeutic: 10-20 mcg/ml
Toxic: >20 mcg/ml
Action: Classified as methylxanthine; a bronchodilator that relaxes the bronchial smooth muscle cells. It also increases renal blood flow, thus producing a diuretic effect, and acts as a CNS stimulant.
Use: Emphysema; chronic bronchitis; asthma; CHF
S/E: CNS - irritability, nervousness, restlessness; tachycardia, hypotension, palpitations; tachypnea, flusihing; nausea, vomiting, GI distress
Nsg. Considerations:
a. Monitor levels
b. Monitor V/S and symptoms of toxicity
c. Clients who smoke tobacco and marijuana require higher doses of this drug
d. Administer with milk or meals if GI distress is present, otherwise give 1-2 hours before meals with water.
Discharge Teachings:
a. Consult with provider before taking OTC drugs
b. Avoide excessive caffeine use
c. Do not crush or chew time-released or enteric-coated preparations

17. Valproic Acid (Depakene, Depakote) - Anti-convulsant
Therapeutic: 50-100 mcg/ml
Toxic: >100 mcg/ml
Use: Absence seisures
S/E: Sedation; tremor, ataxia; nausea, vomiting; prolonged bleeding time. Low incidence of S/E as compared to other anti-convulsants
Nsg. Considerations:
a. Agent of choice in many seizure disorders of young children
b. Do not take with carbonated beverages
c. Take with food
d. Monitor platelets, bleeding time, and liver function tests

*Therapeutic & Toxic level ranges may slightly vary from one source to the other.
Ref: NSNA NCLEX-RN Review, Kaplan Course Book; Saunders Comprehensive Review