Biktarvy
Biktarvy
Generic Name
Biktarvy
Mechanism
- Bictegravir: Competitive inhibitor of HIV‑1 integrase, blocking 3’‑end processing and strand transfer required for viral DNA integration into the host genome.
- Emtricitabine & Tenofovir alafenamide: NRTIs that incorporate into viral DNA, causing chain termination.
- *Combined effect*: Synergistic suppression of viral replication with a single dose, reducing pill burden and minimizing drug–drug interactions.
Pharmacokinetics
| Parameter | Details |
| Absorption | Oral; peak plasma concentration (Cmax) in 2–3 h; bioavailability ~37 % (bictegravir). |
| Distribution | Extensive tissue penetration; protein binding ~12 % (bictegravir). |
| Metabolism | Bictegravir: minimal CYP3A4 involvement; extensive glucuronidation. Emtricitabine & tenofovir alafenamide are prodrugs, metabolized to active forms with negligible CYP metabolism. |
| Elimination | Bictegravir: renal (~70 %) and biliary (~30 %). Fast clearance (t½ ≈ 17 h). < 5 % orally eliminated unchanged. |
| Special Populations | No dose adjustment for hepatic impairment; reduced renal clearance may necessitate monitoring (see monitoring section). |
Indications
- Treatment of HIV‑1 infection in adults who have not received prior antiretroviral therapy or who are experiencing treatment failure with an NRTI‑based regimen.
- Use as first‑line therapy in uncomplicated HIV‑1 with no resistance to integrase inhibitors.
Contraindications
- Contraindicated in patients with:
- Known hypersensitivity to any component.
- Concurrent use of strong CYP3A4 inhibitors (e.g., ketoconazole, ritonavir) that may increase bictegravir levels.
- Warnings:
- Renal impairment: Monitor tenofovir alafenamide exposure; use caution in CrCl <45 mL/min.
- Medication interactions: Potential for increased plasma levels of drugs metabolized by glucuronidation (e.g., carbamazepine).
- Hepatic disease: While no dose adjustment is needed, monitor for hepatotoxicity markers (ALT/AST).
- Drug‑drug interactions: Proximal tubular toxins (e.g., aminoglycosides) may have additive nephrotoxicity.
Dosing
- Standard regimen: One 25 mg bictegravir/200 mg emtricitabine/25 mg tenofovir alafenamide tablet once daily orally, with or without food.
- Initiation: No lead‑in period; start immediately unless contraindications exist.
- Refill: Maintain a 7‑day supply for missed doses; discuss adherence strategies.
Adverse Effects
| Category | Example | Incidence |
| Common | Nausea, headache, insomnia, rash | ≤10 % |
| Adverse metabolic | Mild hyperlipidemia, weight gain | <5 % |
| Renal | Persistent increase in serum creatinine (usually reversible) | ~2 % |
| Hepatic | Elevated transaminases | <3 % |
| Serious | Severe hypersensitivity reactions, hepatic failure, or acute kidney injury (rare) | <0.5 % |
*Note*: Tenofovir alafenamide’s safety profile shows a significantly lower rate of renal and bone toxicity compared with tenofovir disoproxil fumarate.
Monitoring
| Parameter | Frequency | Rationale |
| Baseline labs | CD4 count, HIV‑1 RNA, complete blood count, CMP, creatinine clearance, lipid panel | Establish disease status, organ function |
| HIV‑1 RNA | Every 4 weeks first 3 months, then quarterly | Detect virologic suppression and resistance |
| Renal function | Every 3 months (or more often if CrCl <45 mL/min) | Monitor tenofovir alafenamide impact |
| Liver enzymes | Every 3 months | Detect hepatotoxicity |
| Adherence assessment | Every visit | Ensure optimal outcomes |
| Drug‑drug interactions | At each prescription update | Adjust concomitant therapies as necessary |
Clinical Pearls
- Single‑tablet benefit: Biktarvy’s once‑daily dosing yields >90 % adherence in real‑world studies, translating to superior virologic suppression.
- Bictegravir’s high barrier: Even in the presence of integrase mutations, bictegravir retains activity, making it a strong choice for patients with limited options.
- Tenofovir alafenamide safety: Compared to tenofovir disoproxil fumarate, tenofovir alafenamide is associated with *≈ 90 % lower* risk of renal osteopenia, allowing its use in patients with pre‑existing kidney disease.
- Interaction with rifampin: Ritonavir‑boosted protease inhibitors can *increase* bictegravir levels, necessitating dose adjustment or alternative therapy.
- Adherence counseling: Pair weekly phone check‑ins with a pillbox reminder to optimize long‑term suppression; Biktarvy’s low pill burden simplifies this strategy.
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• Key Takeaway: Biktarvy offers an effective, single‑tablet, once‑daily regimen with a robust pharmacologic profile and a favorable safety data set, making it an excellent first‑line choice for newly diagnosed HIV‑1 patients and those requiring regimen simplification.