What is the recommended dosing regimen for diazepam (Diazepam) and diphenhydramine (Diphenhydramine) prior to an angiogram?

Premedication Dosing for Angiography

For patients undergoing angiography, administer diazepam 5-10 mg IV slowly immediately prior to the procedure, titrating to desired sedative response (such as slurring of speech), with a maximum of 20 mg IV if narcotics are omitted. 1 Diphenhydramine 25-50 mg IV can be added as an adjunct to enhance sedation and reduce required doses of other sedatives, though it is not routinely recommended for standard angiography premedication. 2, 3

Diazepam Dosing Protocol

Standard Dosing for Endoscopic/Angiographic Procedures

• Administer diazepam intravenously with slow titration (at least 1 minute per 5 mg) immediately prior to the procedure to achieve desired sedative response 1
• The typical effective dose is 10 mg IV or less, though up to 20 mg may be given when concomitant narcotics are omitted 1
• If IV access is not feasible, give 5-10 mg IM approximately 30 minutes before the procedure 1
• Reduce narcotic doses by at least one-third when using diazepam, and in some cases narcotics may be omitted entirely 1

Special Population Considerations

• Elderly or debilitated patients require lower doses (usually 2-5 mg) with slow dose escalation 1
• Patients on chronic sedative medications need dose adjustments to avoid excessive sedation 1
• No dose adjustment is required for renal failure patients as diazepam is metabolized hepatically 4

Evidence for Anxiety Reduction

• Research demonstrates that diazepam 5 mg produces modest but significant anxiety reduction compared to no premedication in patients undergoing coronary angiography (ΔVAS=-2.0, p=0.003) 5
• Lorazepam 1 mg sublingual shows equivalent efficacy to diazepam 5 mg for anxiety reduction (ΔVAS=-2.0, p=0.007) 5
• Midazolam 7.5 mg oral did not significantly reduce anxiety compared to no premedication and was associated with a high side effect rate (19.8% of patients) 5

Diphenhydramine Dosing Protocol

Standard Dosing as Sedation Adjunct

• The recommended dose is 25-50 mg IV when used as an adjunct for procedural sedation 2, 3
• Administer slowly IV to minimize hypotension risk 2
• Diphenhydramine reduces required doses of other sedatives: specifically decreasing meperidine requirements by approximately 10 mg and midazolam by 0.6 mg while maintaining equivalent sedation 2

Clinical Context for Use

Diphenhydramine is NOT standard premedication for routine angiography. Its primary indications in the cardiac catheterization setting are:

• Prophylaxis for contrast allergy: 50 mg diphenhydramine 1 hour before procedure in patients with prior anaphylactoid reactions to contrast (combined with prednisone 60 mg the night before and morning of procedure) 4
• Adjunct sedation when enhanced effect is needed: particularly when combining with benzodiazepines to create synergistic sedation 2

Critical Safety Warnings

• Monitor for paradoxical agitation, particularly in younger patients, which cannot be predicted unless previously documented 2
• Watch for hypotension when combining with other CNS depressants, requiring continuous hemodynamic monitoring 2
• The 4-6 hour duration often exceeds procedural needs, potentially extending recovery time 2
• Anticholinergic effects include urinary retention, dry mouth, blurred vision, constipation, and potential delirium in elderly patients 2, 3

Practical Algorithm for Angiography Premedication

Step 1: Assess Patient Risk and Anxiety Level

• For routine diagnostic angiography with mild anxiety: Consider no premedication, as non-pharmacologic approaches are preferred for hemodynamic stability 6
• For moderate to severe anxiety or PCI: Proceed with pharmacologic premedication 5

Step 2: Select Benzodiazepine Strategy

• First-line: Diazepam 5-10 mg IV titrated slowly immediately before procedure 1, 5
• Alternative: Lorazepam 1 mg sublingual if oral route preferred and time permits 5
• Avoid midazolam oral due to lack of efficacy and high side effect rate in this setting 5

Step 3: Consider Diphenhydramine Addition Only If:

• Patient has documented prior contrast allergy (use 50 mg IV as part of prophylaxis protocol with steroids) 4
• Enhanced sedation is specifically needed and patient has no contraindications to anticholinergic effects 2
• Do NOT use routinely for standard angiography premedication 4

Step 4: Adjust Narcotic Dosing

• Reduce narcotic doses by at least one-third when benzodiazepine is administered 1
• Consider omitting narcotics entirely if adequate sedation achieved with benzodiazepine alone 1

Common Pitfalls to Avoid

• Do not confuse contrast allergy prophylaxis with routine premedication: Diphenhydramine is indicated for the former but not the latter 4
• Avoid excessive dosing in elderly patients: Start with 2-5 mg diazepam and titrate slowly 1
• Do not administer IV benzodiazepines rapidly: Take at least 1 minute per 5 mg to avoid respiratory depression 1
• Do not use diphenhydramine as monotherapy for sedation: It requires combination with other agents and continuous monitoring 2
• Ensure respiratory support is immediately available when administering IV sedation 1