Stavudine (Page 4 of 9)

8.5 Geriatric Use

Clinical studies of stavudine did not include sufficient numbers of patients aged 65 years and over to determine whether they respond differently than younger patients. Greater sensitivity of some older individuals to the effects of stavudine cannot be ruled out.

In a monotherapy Expanded Access Program for patients with advanced HIV-1 infection, peripheral neuropathy or peripheral neuropathic symptoms were observed in 15 of 40 (38%) elderly patients receiving 40 mg twice daily and 8 of 51 (16%) elderly patients receiving 20 mg twice daily. Of the approximately 12,000 patients enrolled in the Expanded Access Program, peripheral neuropathy or peripheral neuropathic symptoms developed in 30% of patients receiving 40 mg twice daily and 25% of patients receiving 20 mg twice daily. Elderly patients should be closely monitored for signs and symptoms of peripheral neuropathy.

Stavudine is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, it may be useful to monitor renal function. Dose adjustment is recommended for patients with renal impairment [see Dosage and Administration (2.3)].

8.6 Renal Impairment

Data from two studies in adults indicated that the apparent oral clearance of stavudine decreased and the terminal elimination half-life increased as creatinine clearance decreased. Based on these observations, it is recommended that the stavudine dosage be modified in patients with reduced creatinine clearance and in patients receiving maintenance hemodialysis [see Dosage and Administration (2.3) and Clinical Pharmacology (12.3)].

10 OVERDOSAGE

Experience with adults treated with 12 to 24 times the recommended daily dosage revealed no acute toxicity. Complications of chronic overdosage include peripheral neuropathy and hepatic toxicity. Stavudine can be removed by hemodialysis; the mean ± SD hemodialysis clearance of stavudine is 120 ± 18 mL/min. Whether stavudine is eliminated by peritoneal dialysis has not been studied.

11 DESCRIPTION

Stavudine (d4T) is a synthetic thymidine nucleoside analogue, active against the human immunodeficiency virus type 1 (HIV-1). The chemical name for stavudine is 2′,3′-didehydro-3′-deoxythymidine. Stavudine has the following structural formula:

Stavudine Structural Formula

Stavudine, USP is a white to off-white crystalline solid with the molecular formula C10H12N2O4 and a molecular weight of 224.21. The solubility of stavudine at 23°C is approximately 83 mg/mL in water and 30 mg/mL in propylene glycol. The n-octanol/water partition coefficient of stavudine at 23°C is 0.144.

Stavudine Capsules, USP are supplied for oral administration in strengths of 15 mg, 20 mg, 30 mg or 40 mg of stavudine, USP. Each capsule also contains inactive ingredients: lactose anhydrous, magnesium stearate, microcrystalline cellulose and sodium starch glycolate. The empty hard shell gelatin capsules contain gelatin and titanium dioxide. In addition, the 15 mg empty capsules contain D&C Red No. 28, D&C Yellow No. 10, FD&C Blue No. 1, FD&C Red No. 40, FD&C Yellow No. 6; the 20 mg empty capsules contain D&C Red No. 28, FD&C Blue No. 1, FD&C Red No. 40; the 30 mg empty capsules contain D&C Red No. 28, D&C Yellow No. 10, FD&C Red No. 40, FD&C Yellow No. 6; and the 40 mg empty capsules contain D&C Red No. 28, D&C Yellow No. 10, FD&C Yellow No. 6.

The imprinting ink contains black iron oxide, potassium hydroxide, propylene glycol and shellac.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Stavudine is an antiviral drug [see Clinical Pharmacology (12.4)].

12.3 Pharmacokinetics

The pharmacokinetics of stavudine have been evaluated in HIV-1-infected adult and pediatric patients (Tables 7, 8, and 9). Peak plasma concentrations (Cmax ) and area under the plasma concentration-time curve (AUC) increased in proportion to dose after both single and multiple doses ranging from 0.03 to 4 mg/kg. There was no significant accumulation of stavudine with repeated administration every 6, 8, or 12 hours.

Absorption

Following oral administration, stavudine is rapidly absorbed, with peak plasma concentrations occurring within one hour after dosing. The systemic exposure to stavudine is the same following administration as capsules or solution. Steady-state pharmacokinetic parameters of stavudine in HIV-1-infected adults are shown in Table 7.

Table 7: Steady-State Pharmacokinetic Parameters of Stavudine in HIV-1-Infected
AUC0-24 = Area under the curve over 24 hoursCmax = Maximum plasma concentration Cmin = Trough or minimum plasma concentration
Parameter

Stavudine

40 mg BID

AUC0-24 (ng•h/mL)

Cmax (ng/mL)

min (ng/mL)

2568 ± 454

536 ± 146

Distribution

Binding of stavudine to serum proteins was negligible over the concentration range of 0.01 to 11.4 mcg/mL. Stavudine distributes equally between red blood cells and plasma. Volume of distribution is shown in Table 8.

Metabolism

Metabolism plays a limited role in the clearance of stavudine. Unchanged stavudine was the major drug-related component circulating in plasma after an 80 mg dose of 14 C-stavudine, while metabolites constituted minor components of the circulating radioactivity. Minor metabolites include oxidized stavudine, glucuronide conjugates of stavudine and its oxidized metabolite, and an N-acetylcysteine conjugate of the ribose after glycosidic cleavage, suggesting that thymine is also a metabolite of stavudine.

Elimination

Following an 80 mg dose of 14 C-stavudine to healthy subjects, approximately 95% and 3% of the total radioactivity was recovered in urine and feces, respectively. Radioactivity due to parent drug in urine and feces was 73.7% and 62%, respectively. The mean terminal elimination half-life is approximately 2.3 hours following single oral doses. Mean renal clearance of the parent compound is approximately 272 mL/min, accounting for approximately 67% of the apparent oral clearance.

In HIV-1-infected patients, renal elimination of unchanged drug accounts for about 40% of the overall clearance regardless of the route of administration (Table 8). The mean renal clearance was about twice the average endogenous creatinine clearance, indicating active tubular secretion in addition to glomerular filtration.

Table 8: Pharmacokinetic Parameters of Stavudine in HIV-1-Infected Adults: Bioavailability, Distribution and Clearance
*
Following 1-hour IV infusion
Following single oral dose
Assuming a body weight of 70 kg
§
Over 12 to 24 hours
Parameter Mean ± SD n
Oral bioavailability (%) 86.4 ± 18.2 25
Volume of distribution (L)* 46 ± 21 44
Total body clearance (mL/min)* 594 ± 164 44
Apparent oral clearance (mL/min) 560 ± 182 113
Renal clearance (mL/min)* 237 ± 98 39
Elimination half-life, IV dose (h)* 1.15 ± 0.35 44
Elimination half-life, oral dose (h) 1.6 ± 0.23 8
Urinary recovery of stavudine (% of dose)*§ 42 ± 14 39

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