CNS Drugs & Hemoglobinopathies

Pharmacology of chronic pain, opiates, and the sickle cell patient journey

Chronic Pain Management

Treatment depends on pain type. Your first reach is usually an antidepressant that also quiets pain signals.

Amitriptyline = the default. Heart disease? Switch to Gabapentin. Stabby pain? Carbamazepine wins.
Amitriptyline
TCA for ANY chronic pain
1 Block reuptake of catecholamines → ↑sympathetic tone
2 Strongly anti-cholinergic → hot, dry skin, hyperthermia
3 Block alpha-1 receptors → ↓BP
4 Block AV conduction → ventricular arrhythmias, prolong QT
5 Block Na channels
6 Antihistaminic
Gabapentin
For heart disease patients

SAFE with cardiac history

Avoids amitriptyline's sympathomimetic effects

Use for neuropathic pain when cardiovascular risk is concern

Carbamazepine
Shooting/stabbing pain

SUPERIOR for neuropathic pain

Stabilizes neuronal membrane

Especially effective for shooting, stabbing, or lancinating pain patterns

Opiates & CNS Depressants

Three major actions: CNS depression, muscle relaxation, and analgesia. Receptors matter—mu in brain, kappa in spinal cord.

Pinpoint pupils? → Edinger-Westphal nucleus (CN3). Withdrawal cramps? → smooth muscle was being suppressed.

Receptor Location & Function

Mu (ÎĽ)

Located in: Brain

Primary CNS depression, respiratory depression, pupil constriction

Kappa (Îş)

Located in: Spinal cord

Spinal analgesia, some CNS effects

Key Side Effects

Common Opiates

Heroin, Methadone, Morphine, Meperidine, Codone, Oxycodone, Codeine, Dextromethorphan, Suboxone, Buprenorphine, Loperamide, Diphenoxylate, Fentanyl, Pentazocine, Tincture of Opium

Opioid Receptor Blockers

Naloxone

Fast-acting blocker. IV for acute overdose reversal.

Naltrexone

Longer-acting. Oral maintenance for addiction treatment.

Methylnaltrexone

Peripheral antagonist—reverses constipation without affecting CNS analgesia.

The CNS Depressant Triad

Benzos, Barbiturates, Alcohol, Opiates = ALL slow you down

The Sickle Cell Patient Journey

Click each step to follow the molecular and clinical progression.

1 Autosomal Recessive Inheritance

High prevalence in Africa — natural selection advantage against malaria.

Disease incidence:

  • General population: 1–3%
  • + 1 risk factor: ~10%
  • + 2 risk factors: >20%
2 The Mutation: Position 6 of Beta Chain

Substitution: VALINE (fat-soluble) replaces GLUTAMIC ACID (water-soluble)

Glutamic acid normally: Water-loving, sits on surface of protein, exposed to aqueous environment.

Valine is: Fat-soluble, hydrophobic—wants to hide inside protein.

3 Oxygen Keeps Valine Pushed Out

When Oâ‚‚ is bound: The conformational change keeps valine pushed toward the surface, interacting with water.

Result: Cell stays round. No problems.

Normal RBC
(Oâ‚‚ present)
4 When Oâ‚‚ Disappears: Sickling Begins

Without oxygen: Valine sinks into the protein (hydrophobic interaction). Cell loses its shape.

Polymerization: HbS molecules stick together → cell becomes crescent/sickle-shaped.

Sickled RBC
(Oâ‚‚ absent)
5 Vaso-occlusive Crisis

Sickled cells are rigid and sharp. They jam in small vessels → tissue infarction.

Classic presentation (after 6 months of life): DACTYLITIS (hand-foot swelling)

Sites of crisis:

  • CVA (stroke)
  • Pulmonary infarction / acute chest syndrome
  • Splenic sequestration (sudden anemia, shock)
  • Priapism (painful erection)
6 Acute Management of Vaso-occlusive Crisis

First-line: Oxygen to re-oxygenate tissues

Analgesics: Opiates for severe pain (morphine, meperidine)

For CVA specifically: Exchange transfusion

DO NOT use: tPA or aspirin (not indicated; increases bleeding risk)

7 Long-Term Complications

Functional asplenia (autosplenectomy) by age 6 due to repeated splenic infarcts.

Why this matters: Spleen removes 4 things:

  1. Old RBCs (spherocytes)
  2. Oddly-shaped RBCs (like sickled cells)
  3. Nuclear remnants (Howell-Jolly bodies)
  4. Encapsulated organisms (Strep pneumo, HiB, Meningococcus)

Result: Increased susceptibility to encapsulated bacteria.

Prevention: Pneumococcal vaccine after age 2.

8 Aplastic Crisis

Complete bone marrow suppression → no reticulocytes being produced.

Most common cause (MCC): Parvovirus B-19 (also causes Fifth disease in kids)

Diagnostic clue: Check reticulocyte count — tells if marrow is working.

Low reticulocytes in anemic patient = alarming sign of bone marrow failure.

9 Chronic Management

Hydroxyurea: Increases HbF (fetal hemoglobin) → decreases hypoxia stress on cells.

Transfusions: When anemic AND symptomatic (top reason in USA).

Vaccines: Pneumococcal, HiB, Meningococcal.

HbAS patients (trait): Hematuria from renal papillary necrosis.

Infections = MCC for crises. Prophylactic penicillin in young children.

Hemoglobin C Disease

A different mutation at the same position—but with a completely different consequence.

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