PSYC650 Psychopharmacology

Drug Interactions and Prescriptive Authority for

Psychologists

I got a grip of drugs…

• 320 mg methadone (opiate; 40 mg/d max for opiate dependence)

• 32 mg clonazepam (Klonopin; Benzo, 20 mg/d max for seizure disorder)

• 160 mg temazepam (Restoril; Benzo, 30 mg for insomnia)

• 290 mg propranolol (Inderal; Beta Blocker, 640 mg/day max for angina)

• 2 tablets of Vicodin of unknown dose (probably 500/5)– Acetominophin and hydrocodone (max 8 tabs/24-h)

• 1.5 g “Kind Bud” (Good quality marijuana)• 4 g “Mersh” (Poor quality marijuana)• “Some 151” (Usually rum)

i told u i was hardcore

All Drug interactions are to be avoided

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DisagreeWhat about naloxone or disulfiram?

It’s sometimes okay to give/take drugs that you know will have negative

interactions

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Careful dosing and timing

Most interactions are immediate

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Which of the following impact the

significance of a drug interaction?

Dose

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40%1. Dose2. Route of

administration3. Kidney function4. Liver function

Actually, it’s all of the above…

To avoid drug interactions, use herbs instead because they are safer and do not

interact with medications.

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Herbal Interactions

• Black Cohosh– Increased SSRI and TCA ADRs

• Ginko Biloba– Potentially dangerous rise in trazodone

efficacy (Desyrel; SSRI)• Milk Thistle

– Dangerous rise in efficacy and ADRs for “sedatives”

• St. John’s Wort– Reduced efficacy in SSRIs– Increased ADRs for TCAs– Increaed ADRs for migraine meds

Dealing with ADRs

• Get current and detailed drug histories• Give least possible number of adjuncts• Avoid changing pharmacotherapy• Be careful with narrow TIs• Monitor for interactions whenever

changing pharmacotherapy• Keep in touch with prescribers• Keep your patients informed!

Pharmacodynamic Interactions

• Occur at the site of action• Alcohol and barbiturates• Anticholinergic compound with drug

that has anticholinergic ADRs• Naloxone and Heroin

Pharmacokinetic Interactions: Input

• Tetracycline is the classic example– Don’t take with food: cations bind and

decrease free drug available

• L-DOPA increases absorption• Nutrient

– BRAT diet– pH changes– Affect bile secretion

• Also goes the other way with foods– Alcohol altering B6– Anorectics or nausea-inducing drugs– Constipation or diarrhea

Distribution

• Lithium and salts• Phenytoin displaces warfarin

– Can also create greater concentrations in parts of the body, thus promoting hemorrhage

Output

• Enzyme induction– Increases hepatic metabolism– Takes 2-3 weeks to take full effect– Auto-induction (Tegretol & Trileptal)

• Enxyme inhibition– MAOIs increase sympathomimetic amines (E, NE)– Prozac occupies enzymes that break down 5-HT

(competition for enzymes)– Disufiram and alcohol

• Kidney excretion– Competes for renal tubular secretion– Lithium and diuretics

• Increases renal salts, decreases Lithium excretion, increases Lithium levels

T’s and Blues

• Pentazocine (Talwin; mild opiate) + tripelennamine (antihistamine)

• Synergistic effect roughly equivalent to Heroin

• Used when Heroin not available

• Seizures and death– More prevalent in

crowded living arrangements

Phen-Fen

• Fenfluramine– 5-HT releaser– Suppresses appetite– Drowsiness

• Phentermine– Dopamine agonist– Suppresses appetite– Combats drowsiness

Phen-Fen

• 1992 study demonstrated a loss of 30 lbs on average for 121 obese patients– Starting shot for the Phen-Fen craze

• No safety studies– Speeds up lungs– Increases gastric juices– Sped up heart rate– Irreversible and reversible pulmonary

hypertension• Pulled off the market in 1997

– 24 cases of heart valve damage noted in women who had used Phen-Fen for 1 year

Common ADRs for stimulant

medications include:1. Weight gain2. Apathy3. Hallucinations4. Insomnia

Your patient on Haldol appears sweaty, more confused than usual,

has a high fever, and is experiencing painful muscle rigidity. What’s going on?

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25% 25%25%25%1. Serotonin Syndrome

2. Serum Sickness3. Neuroleptic

Malignant Syndrome

4. Extrapyramidal Side Effects

1010

I feel that, with sufficient training, Psychologists should be permitted the authority to

prescribe psychoactive medications.

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