14.2 Liver Disease, Coagulopathy and Viral Hepatitis

2. Hepatic Disease: Metabolic Impairment, Coagulopathy, and Viral Hepatitis

The liver is the metabolic clearinghouse of the body, responsible for synthesizing plasma proteins, producing bile acids, clearing endobiotics and xenobiotics, and synthesizing coagulation factors.

Impaired Hepatic Drug Clearance and Analgesic Cautions

Hepatocytes express cytochrome P450 (CYP450) microsomal enzymes responsible for Phase I functionalisation (oxidation, reduction, hydrolysis) and Phase II conjugation (glucuronidation, sulfation):

• Local Anaesthetics: Amide local anaesthetics (lidocaine, bupivacaine, mepivacaine, prilocaine) undergo extensive hepatic microsomal metabolism. In advanced liver cirrhosis or end-stage liver disease, reduced functional hepatocyte mass and portosystemic shunting drastically impair systemic clearance, prolonging elimination half-lives and predisposing to Local Anaesthetic Systemic Toxicity (LAST) (perioral tingling, tinnitus, tremors, seizures, cardiotoxicity). In severe liver impairment, the total administered dose of lidocaine should be reduced by 50%.
• The Articaine Advantage: Articaine contains a thiophene ring and an additional ester linkage. Approximately $90%$ of articaine is rapidly hydrolysed into inactive articainic acid by circulating plasma esterases, with only ~10% metabolized by hepatic CYP enzymes. Consequently, articaine is the local anaesthetic of choice in patients with mild-to-moderate hepatic dysfunction.
• Paracetamol in Liver Disease: Paracetamol is metabolised predominantly by safe hepatic glucuronidation and sulfation. A minor fraction (~5–10%) is oxidized by CYP2E1 into the highly toxic electrophile N-acetyl-p-benzoquinone imine (NAPQI), which is immediately conjugated with endogenous hepatic glutathione into non-toxic mercapturic acid. In stable cirrhotic patients, paracetamol remains the safest first-line analgesic, but must be restricted to a maximum daily dose of $2\text{ g/day}$ ($500\text{ mg QDS}$) to avoid glutathione depletion. It is strictly contraindicated in acute fulminant hepatic failure.
• NSAIDs: STRICTLY CONTRAINDICATED in liver cirrhosis. NSAIDs inhibit renal vasodilatory prostaglandins, precipitating hepatorenal syndrome (acute oliguric renal failure). Furthermore, NSAID-induced platelet inhibition and gastric mucosal ulceration dramatically escalate the risk of catastrophic haemorrhage from pre-existing oesophageal varices.

Coagulopathy and Clotting Factor Synthesis Deficiency

With the sole exception of Factor VIII and von Willebrand factor (which are synthesized by vascular endothelial cells), all circulating coagulation factors are synthesized exclusively by hepatocytes: Factor I (fibrinogen), Factor II (prothrombin), Factor V, Factor VII, Factor IX, Factor X, Factor XI, and Factor XII, alongside endogenous anticoagulants (Protein C, Protein S, and antithrombin):

• Vitamin K-Dependent Factors: Synthesis of Factors II, VII, IX, and X requires vitamin K as an essential cofactor. In liver disease, hepatocellular failure or biliary obstruction (which blocks bile salt secretion, impairing intestinal absorption of fat-soluble vitamin K) results in severe factor deficiencies, manifesting as a prolonged Prothrombin Time (PT) / elevated INR and prolonged Activated Partial Thromboplastin Time (APTT).
• Thrombocytopenia in Liver Disease: Cirrhotic architectural remodeling creates high vascular resistance in the portal venous system, driving portal hypertension. This forces retrograde pooling of blood into the splenic vein, producing congestive splenomegaly. The hyperactive spleen sequesters up to 90% of circulating platelets (hypersplenism), causing marked thrombocytopenia. Furthermore, failing hepatocytes synthesize diminished quantities of thrombopoietin (TPO), further suppressing bone marrow megakaryocytopoiesis.

Viral Hepatitis Transmission Risks (HBV, HCV, HDV)

• Transmission: Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV) are blood-borne pathogens transmitted via percutaneous sharps injuries, splashes to mucous membranes, or non-intact skin.
• Transmission Risk following Needlestick Injury:
  • Hepatitis B Virus (HBeAg-positive source): Up to $30%$ transmission risk.
  • Hepatitis C Virus: Approximately $3%$ transmission risk.
  • Human Immunodeficiency Virus (HIV): Approximately $0.3%$ transmission risk.
• Standard Universal Precautions: In UK clinical governance, all patients must be managed with identical, rigorous universal infection control procedures, assuming all bodily fluids are potentially infectious.
• Hepatitis B Immunisation: Dental healthcare personnel must be vaccinated with recombinant hepatitis B surface antigen (HBsAg) at 0, 1, and 6 months. Post-vaccination serological testing for anti-HBs antibodies is performed 1 to 4 months following the primary course:
  • $> 100\text{ mIU/mL}$: Adequate responder. Long-term clinical immunity; no routine booster required.
  • $10-100\text{ mIU/mL}$: Poor responder. Single booster dose recommended; re-test anti-HBs.
  • $< 10\text{ mIU/mL}$: Non-responder. Repeat complete 3-dose course. If still $< 10\text{ mIU/mL}$, evaluate for underlying chronic HBV infection (test for HBsAg) and provide specific counseling regarding immediate Hepatitis B Immunoglobulin (HBIG) administration following any future sharps injury.

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Prescribing Safely in Hepatic Impairment

The practical prescribing rules are examinable in their own right: reduce or avoid drugs with high first-pass metabolism, avoid non-steroidal anti-inflammatory drugs because of gastric and variceal bleeding risk, use paracetamol at a reduced maximum daily dose in significant impairment rather than avoiding it altogether, and use sedatives with great caution because impaired clearance can precipitate hepatic encephalopathy. Alcohol dependence adds its own risks: withdrawal during a hospital admission, poor nutrition and an elevated risk of oral squamous cell carcinoma.